This behavior matches GNU ld and seems reasonable.
```
// If a SECTIONS command is not specified
.text.* -> .text
.rodata.* -> .rodata
.init_array.* -> .init_array
```
A proposed Linux feature CONFIG_FG_KASLR may depend on the GNU ld behavior.
Reword a comment about -z keep-text-section-prefix and a comment about
CommonSection (deleted by rL286234).
Reviewed By: grimar
Differential Revision: https://reviews.llvm.org/D75225
This essentially drops the change by r288021 (discussed with Georgii Rymar
and Peter Smith and noted down in the release note of lld 10).
GNU ld>=2.31 enables -z separate-code by default for Linux x86. By
default (in the absence of a PHDRS command) a readonly PT_LOAD is
created, which is different from its traditional behavior.
Not emulating GNU ld's traditional behavior is good for us because it
improves code consistency (we create a readonly PT_LOAD in the absence
of a SECTIONS command).
Users can add --no-rosegment to restore the previous behavior (combined
readonly and read-executable sections in a single RX PT_LOAD).
Fixes https://bugs.llvm.org/show_bug.cgi?id=44903
It is about the following case:
```
SECTIONS {
.foo : { *(.foo) } =0x90909090
/DISCARD/ : { *(.bar) }
}
```
Here while parsing the fill expression we treated the
"/" of "/DISCARD/" as operator.
With this change, suggested by Fangrui Song, we do
not allow expressions with operators (e.g. "0x1100 + 0x22")
that are not wrapped into round brackets. It should not
be an issue for users, but helps to resolve parsing ambiguity.
Differential revision: https://reviews.llvm.org/D74687
MCTargetOptionsCommandFlags.inc and CommandFlags.inc are headers which contain
cl::opt with static storage.
These headers are meant to be incuded by tools to make it easier to parametrize
codegen/mc.
However, these headers are also included in at least two libraries: lldCommon
and handle-llvm. As a result, when creating DYLIB, clang-cpp holds a reference
to the options, and lldCommon holds another reference. Linking the two in a
single executable, as zig does[0], results in a double registration.
This patch explores an other approach: the .inc files are moved to regular
files, and the registration happens on-demand through static declaration of
options in the constructor of a static object.
[0] https://bugzilla.redhat.com/show_bug.cgi?id=1756977#c5
Differential Revision: https://reviews.llvm.org/D75579
Follow-up for D74433
What the function returns are almost standard BFD names, except that "ELF" is
in uppercase instead of lowercase.
This patch changes "ELF" to "elf" and changes ARM/AArch64 to use their BFD names.
MIPS and PPC64 have endianness differences as well, but this patch does not intend to address them.
Advantages:
* llvm-objdump: the "file format " line matches GNU objdump on ARM/AArch64 objects
* "file format " line can be extracted and fed into llvm-objcopy -O literally.
(https://github.com/ClangBuiltLinux/linux/issues/779 has such a use case)
Affected tools: llvm-readobj, llvm-objdump, llvm-dwarfdump, MCJIT (internal implementation detail, not exposed)
Reviewed By: jhenderson
Differential Revision: https://reviews.llvm.org/D76046
When emitting PDBs, the TypeStreamMerger class is used to merge .debug$T records from the input .OBJ files into the output .PDB stream.
Records in .OBJs are not required to be aligned on 4-bytes, and "The Netwide Assembler 2.14" generates non-aligned records.
When compiling with -DLLVM_ENABLE_ASSERTIONS=ON, an assert was triggered in MergingTypeTableBuilder when non-ghash merging was used.
With ghash merging there was no assert.
As a result, LLD could potentially generate a non-aligned TPI stream.
We now align records on 4-bytes when record indices are remapped, in TypeStreamMerger::remapIndices().
Differential Revision: https://reviews.llvm.org/D75081
Hexagon ABI specifies that call x@gdplt is transformed to call __tls_get_addr.
Example:
call x@gdplt
is changed to
call __tls_get_addr
When x is an external tls variable.
Differential Revision: https://reviews.llvm.org/D74443
Any OUTPUT_FORMAT in a linker script overrides the emulation passed on
the command line, so record the passed bfdname and use that in the error
message about incompatible input files.
This prevents confusing error messages. For example, if you explicitly
pass `-m elf_x86_64` to LLD but accidentally include a linker script
which sets `OUTPUT_FORMAT(elf32-i386)`, LLD would previously complain
about your input files being compatible with elf_x86_64, which isn't the
actual issue, and is confusing because the input files are in fact
x86-64 ELF files.
Interestingly enough, this also prevents a segfault! When we don't pass
`-m` and we have an object file which is incompatible with the
`OUTPUT_FORMAT` set by a linker script, the object file is checked for
compatibility before it's added to the objectFiles vector.
config->emulation, objectFiles, and sharedFiles will all be empty, so
we'll attempt to access bitcodeFiles[0], but bitcodeFiles is also empty,
so we'll segfault. This commit prevents the segfault by adding
OUTPUT_FORMAT as a possible source of machine configuration, and it also
adds an llvm_unreachable to diagnose similar issues in the future.
Differential Revision: https://reviews.llvm.org/D76109
On an internal target,
* Before D74773: time -f '%M' => 18275680
* After D74773: time -f '%M' => 22088964
This patch restores to the status before D74773.
-M output can be useful when diagnosing an "error: output file too large" problem (emitted in openFile()).
I just ran into such a situation where I had to debug an erronerous
Linux kernel linker script. It tried to create a file larger than
INT64_MAX bytes.
This patch could have helped https://bugs.llvm.org/show_bug.cgi?id=44715 as well.
Reviewed By: grimar
Differential Revision: https://reviews.llvm.org/D75966
See `docs/ELF/linker_script.rst` for the new computation for sh_addr and sh_addralign.
`ALIGN(section_align)` now means: "increase alignment to section_align"
(like yet another input section requirement).
The "start of section .foo changes from 0x11 to 0x20" warning no longer
makes sense. Change it to warn if sh_addr%sh_addralign!=0.
To decrease the alignment from the default max_input_align,
use `.output ALIGN(8) : {}` instead of `.output : ALIGN(8) {}`
See linkerscript/section-address-align.test as an example.
When both an output section address and ALIGN are set (can be seen as an
"undefined behavior" https://sourceware.org/ml/binutils/2020-03/msg00115.html),
lld may align more than GNU ld, but it makes a linker script working
with GNU ld hard to break with lld.
This patch can be considered as restoring part of the behavior before D74736.
Differential Revision: https://reviews.llvm.org/D75724
LLD implements Linker Scripts as they are described in the GNU ld manual.
This description is far from a specification, with the only true reference
the GNU ld implementation, which has undocumented behaviour that can vary
from release to release.
To make it easy for people to switch between linkers we try to follow GNU
ld implementation details wherever possible. We reserve the right to make
our own decisions where the undocumented GNU ld behaviour is not
appropriate for LLD. We don't have a place to document these decisions and
it can be difficult for users to find out this information.
This file is a statement of the LLD implementation policy and will contain
intentional deviations from GNU ld.
The first patch that will add concrete details to this file is D75724
Differential Revision: https://reviews.llvm.org/D75921
Summary:
Places orphan sections into a unique output section. This prevents the merging of orphan sections of the same name.
Matches behaviour of GNU ld --unique. --unique=pattern is not implemented.
Motivated user case shown in the test has 2 local symbols as they would appear if C++ source has been compiled with -ffunction-sections. The merging of these sections in the case of a partial link (-r) may limit the effectiveness of -gc-sections of a subsequent link.
Reviewers: espindola, jhenderson, bd1976llvm, edd, andrewng, JonChesterfield, MaskRay, grimar, ruiu, psmith
Reviewed By: MaskRay, grimar
Subscribers: emaste, arichardson, MaskRay, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D75536
```
createFiles(args)
readDefsym
readerLinkerScript(*mb)
...
readMemory
readMemoryAssignment("ORIGIN", "org", "o") // eagerly evaluated
target = getTarget();
link(args)
writeResult<ELFT>()
...
finalizeSections()
script->processSymbolAssignments()
addSymbol(cmd) // with this patch, evaluated here
```
readMemoryAssignment eagerly evaluates ORIGIN/LENGTH and returns an uint64_t.
This patch postpones the evaluation to make
* --defsym and symbol assignments
* `CONSTANT(COMMONPAGESIZE)` (requires a non-null `lld:🧝:target`)
work. If the expression somehow requires interaction with memory
regions, the circular dependency may cause the expression to evaluate to
a strange value. See the new test added to memory-err.s
Reviewed By: grimar
Differential Revision: https://reviews.llvm.org/D75763
lld/.clang-tidy is almost identical to the top-level .clang-tidy, with the aforementioned customization.
Reviewed By: ruiu
Differential Revision: https://reviews.llvm.org/D75809
Added a write method for TimeTrace that takes two strings representing
file names. The first is any file name that may have been provided by the
user via `time-trace-file` flag, and the second is a fallback that should
be configured by the caller. This method makes it cleaner to write the
trace output because there is no longer a need to check file names at the
caller and simplifies future TimeTrace usages.
Reviewed By: modocache
Differential Revision: https://reviews.llvm.org/D74514
llvm::call_once(initDwarfLine, [this]() { initializeDwarf(); });
Though it is not used in all places.
I need that patch for implementing "Remove obsolete debug info" feature
(D74169). But this caching mechanism is useful by itself, and I think it
would be good to use it without connection to "Remove obsolete debug info"
feature. So this patch changes inplace creation of DWARFContext with
its cached version.
Depends on D74308
Reviewed By: ruiu
Differential Revision: https://reviews.llvm.org/D74773
Currently `yaml2obj` require `Offset` field in a relocation description.
There are many cases when `Offset` is insignificant in a context of a test case.
Making `Offset` optional allows to simplify our test cases.
This is what this patch does.
Also, with this patch `obj2yaml` does not dump a zero offset of a relocation.
Differential revision: https://reviews.llvm.org/D75608
The new behavior matches GNU objdump. A pair of angle brackets makes tests slightly easier.
`.foo:` is not unique and thus cannot be used in a `CHECK-LABEL:` directive.
Without `-LABEL`, the CHECK line can match the `Disassembly of section`
line and causes the next `CHECK-NEXT:` to fail.
```
Disassembly of section .foo:
0000000000001634 .foo:
```
Bdragon: <> has metalinguistic connotation. it just "feels right"
Reviewed By: rupprecht
Differential Revision: https://reviews.llvm.org/D75713
* Delete boilerplate
* Change functions to return `Error`
* Test parsing errors
* Update callers of ARMAttributeParser::parse() to check the `Error` return value.
Since this patch touches nearly everything in the file, I apply
http://llvm.org/docs/Proposals/VariableNames.html and change variable
names to lower case.
Reviewed By: compnerd
Differential Revision: https://reviews.llvm.org/D75015
This fixes several issues. The behavior changes are:
A SHN_COMMON symbol does not have the 'g' flag.
An undefined symbol does not have 'g' or 'l' flag.
A STB_GLOBAL SymbolRef::ST_Unknown symbol has the 'g' flag.
A STB_LOCAL SymbolRef::ST_Unknown symbol has the 'l' flag.
Reviewed By: rupprecht
Differential Revision: https://reviews.llvm.org/D75659
This changes the output of `llvm-readelf -n` from:
```
Displaying notes found at file offset 0x<...> with length 0x<...>:
```
to:
```
Displaying notes found in: .note.foo
```
And similarly, adds a `Name:` field to the `llvm-readobj -n` output for notes.
This change not only increases GNU compatibility, it also makes it much easier to read notes. Note that we still fall back to printing the file offset/length in cases where we don't have a section name, such as when printing notes in program headers or printing notes in a partially stripped file (GNU readelf does the same).
Fixes llvm.org/PR41339.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D75647
Summary:
LLD has workaround for the times when SectionIndex was not passed properly:
LT->getFileLineInfoForAddress(
S->getOffsetInFile() + Offset, nullptr,
DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath, Info));
S->getOffsetInFile() was added to differentiate offsets between
various sections. Now SectionIndex is properly specified.
Thus it is not necessary to use getOffsetInFile() workaround.
See https://reviews.llvm.org/D58194, https://reviews.llvm.org/D58357.
This patch removes getOffsetInFile() workaround.
Reviewers: ruiu, grimar, MaskRay, espindola
Reviewed By: grimar, MaskRay
Subscribers: emaste, arichardson, llvm-commits
Tags: #llvm, #lld
Differential Revision: https://reviews.llvm.org/D75636
Summary:
A test is passing `-o -` to lld in the hope of writing the output to
standard out but that is not the case. Instead it creates a file named
`-.lto.o`. This fixes it by creating a temporary file in the work
directory.
Differential Revision: https://reviews.llvm.org/D75605
and follow-ups:
a2ca1c2d "build: disable zlib by default on Windows"
2181bf40 "[CMake] Link against ZLIB::ZLIB"
1079c68a "Attempt to fix ZLIB CMake logic on Windows"
This changed the output of llvm-config --system-libs, and more
importantly it broke stand-alone builds. Instead of piling on more fix
attempts, let's revert this to reduce the risk of more breakages.
Otherwise ld.lld -save-temps will crash when writing to ResolutionFile.
llvm-lto2 -save-temps does not crash because it exits immediately.
Reviewed By: evgeny777
Differential Revision: https://reviews.llvm.org/D75426
Similar to D63182 [ELF][PPC64] Don't report "relocation refers to a discarded section" for .toc
Reviewed By: Bdragon28
Differential Revision: https://reviews.llvm.org/D75419
Summary:
Extracted from D74773. Currently, errors happened while parsing
debug info are reported as errors. DebugInfoDWARF library treats such
errors as "Recoverable errors". This patch makes debug info errors
to be reported as warnings, to support DebugInfoDWARF approach.
Reviewers: ruiu, grimar, MaskRay, jhenderson, espindola
Reviewed By: MaskRay, jhenderson
Subscribers: emaste, aprantl, arichardson, arphaman, llvm-commits
Tags: #llvm, #debug-info, #lld
Differential Revision: https://reviews.llvm.org/D75234
When there are both strong and weak references to an undefined
symbol ensure that the strong reference prevails in the output symbol
generating the correct error.
Test case copied from lld/test/ELF/weak-and-strong-undef.s
Differential Revision: https://reviews.llvm.org/D75322
MC will now output the R_ARM_THM_PC8, R_ARM_THM_PC12 and
R_ARM_THM_PREL_11_0 relocations. These are short-ranged relocations that
are used to implement the adr rd, literal and ldr rd, literal pseudo
instructions.
The instructions use a new RelExpr called R_ARM_PCA in order to calculate
the required S + A - Pa expression, where Pa is AlignDown(P, 4) as the
instructions add their immediate to AlignDown(PC, 4). We also do not want
these relocations to generate or resolve against a PLT entry as the range
of these relocations is so short they would never reach.
The R_ARM_THM_PC8 has a special encoding convention for the relocation
addend, the immediate field is unsigned, yet the addend must be -4 to
account for the Thumb PC bias. The ABI (not the architecture) uses the
convention that the 8-byte immediate of 0xff represents -4.
Differential Revision: https://reviews.llvm.org/D75042
WebAssembly requires that caller and callee signatures match, so it
can't do the usual trick of passing more arguments to main than it
expects. Instead WebAssembly will mangle "main" with argc/argv
parameters as "__main_argc_argv". This patch teaches lld how to
demangle it.
This patch is part of https://reviews.llvm.org/D70700.
They are purposefully skipped by input section descriptions (rL295324).
Similarly, --orphan-handling= should not warn/error for them.
This behavior matches GNU ld.
Reviewed By: grimar
Differential Revision: https://reviews.llvm.org/D75151
This makes --orphan-handling= less noisy.
This change also improves our compatibility with GNU ld.
GNU ld special cases .symtab, .strtab and .shstrtab . We need output section
descriptions for .symtab, .strtab and .shstrtab to suppress:
<internal>:(.symtab) is being placed in '.symtab'
<internal>:(.shstrtab) is being placed in '.shstrtab'
<internal>:(.strtab) is being placed in '.strtab'
With --strip-all, .symtab and .strtab can be omitted (note, --strip-all is not compatible with --emit-relocs).
Reviewed By: nickdesaulniers
Differential Revision: https://reviews.llvm.org/D75149
Instead, use `using namespace lld(::coff)`, and fully qualify the names
of free functions where they are defined in cpp files.
This effectively reverts d79c3be618 to follow the new style guide added
in 236fcbc21a.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D74882
While the value of the CIE pointer field in a DWARF FDE record is
an offset to the corresponding CIE record from the beginning of
the section, for EH FDE records it is relative to the current offset.
Previously, we did not make that distinction when dumped both kinds
of FDE records and just printed the same value for the CIE pointer
field and the CIE offset; that was acceptable for DWARF FDEs but was
wrong for EH FDEs.
This patch fixes the issue by explicitly printing the offset of the
linked CIE object.
Differential Revision: https://reviews.llvm.org/D74613
With this --shuffle-sections=seed produces the same result in every
host.
Reviewed By: grimar, MaskRay
Differential Revision: https://reviews.llvm.org/D74971
When the output section address (addrExpr) is specified, GNU ld warns if
sh_addr is different. This patch implements the warning.
Note, LinkerScript::assignAddresses can be called more than once. We
need to record the changed section addresses, and only report the
warnings after the addresses are finalized.
Reviewed By: grimar
Differential Revision: https://reviews.llvm.org/D74741
Follow-up for D74286.
Notations:
* alignExpr: the computed ALIGN value
* max_input_align: the maximum of input section alignments
This patch changes the following two cases to match GNU ld:
* When ALIGN is present, GNU ld sets output sh_addr to alignExpr, while lld use max(alignExpr, max_input_align)
* When addrExpr is specified but alignExpr is not, GNU ld sets output sh_addr to addrExpr, while lld uses `advance(0, max_input_align)`
Note, sh_addralign is still set to max(alignExpr, max_input_align).
lma-align.test is enhanced a bit to check we don't overalign sh_addr.
fixSectionAlignments() sets addrExpr but not alignExpr for the `!hasSectionsCommand` case.
This patch sets alignExpr as well so that max_input_align will be respected.
Reviewed By: grimar
Differential Revision: https://reviews.llvm.org/D74736
The changes the in-memory representation of wasm symbols such that their
optional ImportName and ImportModule use llvm::Optional.
ImportName is set whenever WASM_SYMBOL_EXPLICIT_NAME flag is set.
ImportModule (for imports) is currently always set since it defaults to
"env".
In the future we can possibly extent to binary format distingish
import which have explit module names.
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D74109
Summary:
This option causes lld to shuffle sections by assigning different
priorities in each run.
The use case for this is to introduce randomization in benchmarks. The
idea is inspired by the paper "Producing Wrong Data Without Doing
Anything Obviously Wrong!"
(https://www.inf.usi.ch/faculty/hauswirth/publications/asplos09.pdf). Unlike
the paper, we shuffle individual sections, not just input files.
Doing this in lld is particularly convenient as the --reproduce option
makes it easy to collect all the necessary bits for relinking the
program being benchmarked. Once that it is done, all that is needed is
to add --shuffle-sections=0 to the response file and relink before each
run of the benchmark.
Differential Revision: https://reviews.llvm.org/D74791
With this patch lld recognizes ARM SBREL relocations.
R_ARM*_MOVW_BREL relocations are not tested because they are not used.
Patch by Tamas Petz
Differential Revision: https://reviews.llvm.org/D74604
Summary:
Generate PAC protected plt only when "-z pac-plt" is passed to the
linker. GNU toolchain generates when it is explicitly requested[1].
When pac-plt is requested then set the GNU_PROPERTY_AARCH64_FEATURE_1_PAC
note even when not all function compiled with PAC but issue a warning.
Harmonizing the warning style for BTI/PAC/IBT.
Generate BTI protected PLT if case of "-z force-bti".
[1] https://www.sourceware.org/ml/binutils/2019-03/msg00021.html
Reviewers: peter.smith, espindola, MaskRay, grimar
Reviewed By: peter.smith, MaskRay
Subscribers: tatyana-krasnukha, emaste, arichardson, kristof.beyls, MaskRay, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D74537
The goal of this patch is to maximize CPU utilization on multi-socket or high core count systems, so that parallel computations such as LLD/ThinLTO can use all hardware threads in the system. Before this patch, on Windows, a maximum of 64 hardware threads could be used at most, in some cases dispatched only on one CPU socket.
== Background ==
Windows doesn't have a flat cpu_set_t like Linux. Instead, it projects hardware CPUs (or NUMA nodes) to applications through a concept of "processor groups". A "processor" is the smallest unit of execution on a CPU, that is, an hyper-thread if SMT is active; a core otherwise. There's a limit of 32-bit processors on older 32-bit versions of Windows, which later was raised to 64-processors with 64-bit versions of Windows. This limit comes from the affinity mask, which historically is represented by the sizeof(void*). Consequently, the concept of "processor groups" was introduced for dealing with systems with more than 64 hyper-threads.
By default, the Windows OS assigns only one "processor group" to each starting application, in a round-robin manner. If the application wants to use more processors, it needs to programmatically enable it, by assigning threads to other "processor groups". This also means that affinity cannot cross "processor group" boundaries; one can only specify a "preferred" group on start-up, but the application is free to allocate more groups if it wants to.
This creates a peculiar situation, where newer CPUs like the AMD EPYC 7702P (64-cores, 128-hyperthreads) are projected by the OS as two (2) "processor groups". This means that by default, an application can only use half of the cores. This situation could only get worse in the years to come, as dies with more cores will appear on the market.
== The problem ==
The heavyweight_hardware_concurrency() API was introduced so that only *one hardware thread per core* was used. Once that API returns, that original intention is lost, only the number of threads is retained. Consider a situation, on Windows, where the system has 2 CPU sockets, 18 cores each, each core having 2 hyper-threads, for a total of 72 hyper-threads. Both heavyweight_hardware_concurrency() and hardware_concurrency() currently return 36, because on Windows they are simply wrappers over std:🧵:hardware_concurrency() -- which can only return processors from the current "processor group".
== The changes in this patch ==
To solve this situation, we capture (and retain) the initial intention until the point of usage, through a new ThreadPoolStrategy class. The number of threads to use is deferred as late as possible, until the moment where the std::threads are created (ThreadPool in the case of ThinLTO).
When using hardware_concurrency(), setting ThreadCount to 0 now means to use all the possible hardware CPU (SMT) threads. Providing a ThreadCount above to the maximum number of threads will have no effect, the maximum will be used instead.
The heavyweight_hardware_concurrency() is similar to hardware_concurrency(), except that only one thread per hardware *core* will be used.
When LLVM_ENABLE_THREADS is OFF, the threading APIs will always return 1, to ensure any caller loops will be exercised at least once.
Differential Revision: https://reviews.llvm.org/D71775
This reverts commit 80a34ae311 with fixes.
Previously, since bots turning on EXPENSIVE_CHECKS are essentially turning on
MachineVerifierPass by default on X86 and the fact that
inline-asm-avx-v-constraint-32bit.ll and inline-asm-avx512vl-v-constraint-32bit.ll
are not expected to generate functioning machine code, this would go
down to `report_fatal_error` in MachineVerifierPass. Here passing
`-verify-machineinstrs=0` to make the intent explicit.
This reverts commit 80a34ae311 with fixes.
On bots llvm-clang-x86_64-expensive-checks-ubuntu and
llvm-clang-x86_64-expensive-checks-debian only,
llc returns 0 for these two tests unexpectedly. I tweaked the RUN line a little
bit in the hope that LIT is the culprit since this change is not in the
codepath these tests are testing.
llvm\test\CodeGen\X86\inline-asm-avx-v-constraint-32bit.ll
llvm\test\CodeGen\X86\inline-asm-avx512vl-v-constraint-32bit.ll
Fixes https://bugs.llvm.org//show_bug.cgi?id=44878
When --strip-debug is specified, .debug* are removed from inputSections
while .rel[a].debug* (incorrectly) remain.
LinkerScript::addOrphanSections() requires the output section of a relocated
InputSectionBase to be created first.
.debug* are not in inputSections ->
output sections .debug* are not created ->
getOutputSectionName(.rel[a].debug*) dereferences a null pointer.
Fix the null pointer dereference by deleting .rel[a].debug* from inputSections as well.
Reviewed By: grimar, nickdesaulniers
Differential Revision: https://reviews.llvm.org/D74510
Recommit of 0b4a047bfb
(reverted in c29003813a) to incorporate
subsequent fix and add a warning when LLD's interworking behavior has
changed.
D73474 disabled the generation of interworking thunks for branch
relocations to non STT_FUNC symbols. This patch handles the case of BL and
BLX instructions to non STT_FUNC symbols. LLD would normally look at the
state of the caller and the callee and write a BL if the states are the
same and a BLX if the states are different.
This patch disables BL/BLX substitution when the destination symbol does
not have type STT_FUNC. This brings our behavior in line with GNU ld which
may prevent difficult to diagnose runtime errors when switching to lld.
This change does change how LLD handles interworking of symbols that do not
have type STT_FUNC from previous versions including the 10.0 release. This
brings LLD in line with ld.bfd but there may be programs that have not been
linked with ld.bfd that depend on LLD's previous behavior. We emit a warning
when the behavior changes.
A summary of the difference between 10.0 and 11.0 is that for symbols
that do not have a type of STT_FUNC LLD will not change a BL to a BLX or
vice versa. The table below enumerates the changes
| relocation | STT_FUNC | bit(0) | in | 10.0- out | 11.0+ out |
| R_ARM_CALL | no | 1 | BL | BLX | BL |
| R_ARM_CALL | no | 0 | BLX | BL | BLX |
| R_ARM_THM_CALL | no | 1 | BLX | BL | BLX |
| R_ARM_THM_CALL | no | 0 | BL | BLX | BL |
Differential Revision: https://reviews.llvm.org/D73542
We do not keep the actual value of the CIE ID field, because it is
predefined, and use a constant when dumping a CIE record. The issue
was that the predefined value is different for .debug_frame and
.eh_frame sections, but we always printed the one which corresponds
to .debug_frame. The patch fixes that by choosing an appropriate
constant to print.
See the following for more information about .eh_frame sections:
https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html
Differential Revision: https://reviews.llvm.org/D73627
Summary:
Even though this test is a check for failure, lld still attempts
to open the final output file, which fails when the default "a.out"
file is used and the current directory is read-only. Specifying an
output file works around this problem.
Reviewers: espindola
Subscribers: emaste, MaskRay, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D74523
D43468+D44380 added INSERT [AFTER|BEFORE] for non-orphan sections. This patch
makes INSERT work for orphan sections as well.
`SECTIONS {...} INSERT [AFTER|BEFORE] .foo` does not set `hasSectionCommands`, so the result
will be similar to a regular link without a linker script. The differences when `hasSectionCommands` is set include:
* image base is different
* -z noseparate-code/-z noseparate-loadable-segments are unavailable
* some special symbols such as `_end _etext _edata` are not defined
The behavior is similar to GNU ld:
INSERT is not considered an external linker script.
This feature makes the section layout more flexible. It can be used to:
* Place .nv_fatbin before other readonly SHT_PROGBITS sections to mitigate relocation overflows.
* Disturb the layout to expose address sensitive application bugs.
Reviewed By: grimar
Differential Revision: https://reviews.llvm.org/D74375
GNU ld has a counterintuitive lang_propagate_lma_regions rule.
```
// .foo's LMA region is propagated to .bar because their VMA region is the same,
// and .bar does not have an explicit output section address (addr_tree).
.foo : { *(.foo) } >RAM AT> FLASH
.bar : { *(.bar) } >RAM
// An explicit output section address disables propagation.
.foo : { *(.foo) } >RAM AT> FLASH
.bar . : { *(.bar) } >RAM
```
In both cases, lld thinks .foo's LMA region is propagated and
places .bar in the same PT_LOAD, so lld diverges from GNU ld w.r.t. the
second case (lma-align.test).
This patch changes Writer<ELFT>::createPhdrs to disable propagation
(start a new PT_LOAD). A user of the first case can make linker scripts
portable by explicitly specifying `AT>`. By contrast, there was no
workaround for the old behavior.
This change uncovers another LMA related bug in assignOffsets() where
`ctx->lmaOffset = 0;` was omitted. It caused a spurious "load address
range overlaps" error for at2.test
The new PT_LOAD rule is complex. For convenience, I listed the origins of some subexpressions:
* rL323449: `sec->memRegion == load->firstSec->memRegion`; linkerscript/at3.test
* D43284: `load->lastSec == Out::programHeaders` (don't start a new PT_LOAD after program headers); linkerscript/at4.test
* D58892: `sec != relroEnd` (start a new PT_LOAD after PT_GNU_RELRO)
Reviewed By: psmith
Differential Revision: https://reviews.llvm.org/D74297
When lmaRegion is non-null, respect `sec->alignment`
This rule is analogous to `switchTo(sec)` which advances sh_addr (VMA).
This fixes the p_paddr misalignment issue as reported by
https://android-review.googlesource.com/c/trusty/external/trusted-firmware-a/+/1230058
Note, `sec->alignment` is the maximum of ALIGN and input section alignments. We may overalign LMA than GNU ld.
linkerscript/align-lma.s has a FIXME that demonstrates another bug:
`.bss ... >RAM` should be placed in a different PT_LOAD (GNU ld
behavior) because its lmaRegion (nullptr) is different from the previous
section's lmaRegion (ROM).
Reviewed By: psmith
Differential Revision: https://reviews.llvm.org/D74286
Summary:
GNU objdump prints the file format in lowercase, e.g. `elf64-x86-64`. llvm-objdump prints `ELF64-x86-64` right now, even though piping that into llvm-objcopy refuses that as a valid arch to use.
As an example of a problem this causes, see: https://github.com/ClangBuiltLinux/linux/issues/779
Reviewers: MaskRay, jhenderson, alexshap
Reviewed By: MaskRay
Subscribers: tpimh, sbc100, grimar, jvesely, nhaehnle, kerbowa, cfe-commits, llvm-commits
Tags: #clang, #llvm
Differential Revision: https://reviews.llvm.org/D74433
Also remove some test duplication and add a test case that shows the
maximum version is rejected (this also shows that the value in the error
message is actually in decimal, and not just missing an 0x prefix).
Reviewed by: dblaikie
Differential Revision: https://reviews.llvm.org/D74403
This reverts commit rGcd5b308b828e, rGcd5b308b828e, rG8cedf0e2994c.
There are issues to be investigated for polly bots and bots turning on
EXPENSIVE_CHECKS.
This can happen if lto::LTO::getRuntimeLibcallSymbols doesn't return
an complete/accurate list of libcalls. In this case new bitcode
object can be linked in after LTO.
For example the WebAssembly backend currently calls:
setLibcallName(RTLIB::FPROUND_F32_F16, "__truncsfhf2");
But `__truncsfhf2` is not part of `getRuntimeLibcallSymbols` so if
this symbol is generated during LTO the link will currently fail.
Without this change the linker crashes because the bitcode symbol
makes it all the way to the output phase.
See: https://bugs.llvm.org/show_bug.cgi?id=44353
Differential Revision: https://reviews.llvm.org/D71632
There are still problems after the fix in
"[ELF][ARM] Fix regression of BL->BLX substitution after D73542"
so let's revert to get trunk back to green while we investigate.
See https://reviews.llvm.org/D73542
This reverts commit 5461fa2b1f.
This reverts commit 0b4a047bfb.
This adds some of LLD specific scopes and picks up optimisation scopes
via LTO/ThinLTO. Makes use of TimeProfiler multi-thread support added in
77e6bb3c.
Differential Revision: https://reviews.llvm.org/D71060
D73542 made a typo (`rel.type == R_PLT_PC`; should be `rel.expr`) and introduced a regression:
BL->BLX substitution was disabled when the target symbol is preemptible
(expr is R_PLT_PC).
The two added bl instructions in arm-thumb-interwork-shared.s check that
we patch BL to BLX.
Fixes https://bugs.chromium.org/p/chromium/issues/detail?id=1047531
For an out-of-range relocation referencing a non-local symbol, report the symbol name and the object file that defines the symbol. As an example:
```
t.o:(function func: .text.func+0x3): relocation R_X86_64_32S out of range: -281474974609120 is not in [-2147483648, 2147483647]
```
=>
```
t.o:(function func: .text.func+0x3): relocation R_X86_64_32S out of range: -281474974609120 is not in [-2147483648, 2147483647]; references func
>>> defined in t1.o
```
Reviewed By: grimar
Differential Revision: https://reviews.llvm.org/D73518
D73474 disabled the generation of interworking thunks for branch
relocations to non STT_FUNC symbols. This patch handles the case of BL and
BLX instructions to non STT_FUNC symbols. LLD would normally look at the
state of the caller and the callee and write a BL if the states are the
same and a BLX if the states are different.
This patch disables BL/BLX substitution when the destination symbol does
not have type STT_FUNC. This brings our behavior in line with GNU ld which
may prevent difficult to diagnose runtime errors when switching to lld.
Differential Revision: https://reviews.llvm.org/D73542
Many of the debug line prologue errors are not inherently fatal. In most
cases, we can make reasonable assumptions and carry on. This patch does
exactly that. In the case of length problems, the approach of "assume
stated length is correct" is taken which means the offset might need
adjusting.
This is a relanding of b94191fe, fixing an LLD test and the LLDB build.
Reviewed by: dblaikie, labath
Differential Revision: https://reviews.llvm.org/D72158
This is how it should've been and brings it more in line with
std::string_view. There should be no functional change here.
This is mostly mechanical from a custom clang-tidy check, with a lot of
manual fixups. It uncovers a lot of minor inefficiencies.
This doesn't actually modify StringRef yet, I'll do that in a follow-up.
Similar to R_MIPS_GPREL16 and R_MIPS_GPREL32 (D45972).
If the addend of an R_PPC_PLTREL24 is >= 0x8000, it indicates that r30
is relative to the input section .got2.
```
addis 30, 30, .got2+0x8000-.L1$pb@ha
addi 30, 30, .got2+0x8000-.L1$pb@l
...
bl foo+0x8000@PLT
```
After linking, the relocation will be relative to the output section .got2.
To compensate for the shift `address(input section .got2) - address(output section .got2) = ppc32Got2OutSecOff`, adjust by `ppc32Got2OutSecOff`:
```
addis 30, 30, .got2+0x8000-.L1+ppc32Got2OutSecOff$pb@ha
addi 30, 30, .got2+0x8000-.L1+ppc32Got2OutSecOff$pb@ha$pb@l
...
bl foo+0x8000+ppc32Got2OutSecOff@PLT
```
This rule applys to a relocatable link or a non-relocatable link with --emit-relocs.
Reviewed By: Bdragon28
Differential Revision: https://reviews.llvm.org/D73532
In ErrorHandler::error(), rearrange code to avoid calling exitLld with
the mutex locked. Acquire mutex lock when flushing the output streams in
exitLld.
Differential Revision: https://reviews.llvm.org/D73281
ELF for the ARM architecture requires linkers to provide
interworking for symbols that are of type STT_FUNC. Interworking for
other symbols must be encoded directly in the object file. LLD was always
providing interworking, regardless of the symbol type, this breaks some
programs that have branches from Thumb state targeting STT_NOTYPE symbols
that have bit 0 clear, but they are in fact internal labels in a Thumb
function. LLD treats these symbols as ARM and inserts a transition to Arm.
This fixes the problem for in range branches, R_ARM_JUMP24,
R_ARM_THM_JUMP24 and R_ARM_THM_JUMP19. This is expected to be the vast
majority of problem cases as branching to an internal label close to the
function.
There is at least one follow up patch required.
- R_ARM_CALL and R_ARM_THM_CALL may do interworking via BL/BLX
substitution.
In theory range-extension thunks can be altered to not change state when
the symbol type is not STT_FUNC. I will need to check with ld.bfd to see if
this is the case in practice.
Fixes (part of) https://github.com/ClangBuiltLinux/linux/issues/773
Differential Revision: https://reviews.llvm.org/D73474
This restores 59733525d3 (D71913), along
with bot fix 19c76989bb.
The bot failure should be fixed by D73418, committed as
af954e441a.
I also added a fix for non-x86 bot failures by requiring x86 in new test
lld/test/ELF/lto/devirt_vcall_vis_public.ll.
* Generalize the code added in D70637 and D70937. We should eventually remove the EM_MIPS special case.
* Handle R_PPC_LOCAL24PC the same way as R_PPC_REL24.
Reviewed By: Bdragon28
Differential Revision: https://reviews.llvm.org/D73424
-fno-pie produces a pair of non-GOT-non-PLT relocations R_PPC_ADDR16_{HA,LO} (R_ABS) referencing external
functions.
```
lis 3, func@ha
la 3, func@l(3)
```
In a -no-pie/-pie link, if func is not defined in the executable, a canonical PLT entry (st_value>0, st_shndx=0) will be needed.
References to func in shared objects will be resolved to this address.
-fno-pie -pie should fail with "can't create dynamic relocation ... against ...", so we just need to think about -no-pie.
On x86, the PLT entry passes the JMP_SLOT offset to the rtld PLT resolver.
On x86-64: the PLT entry passes the JUMP_SLOT index to the rtld PLT resolver.
On ARM/AArch64: the PLT entry passes &.got.plt[n]. The PLT header passes &.got.plt[fixed-index]. The rtld PLT resolver can compute the JUMP_SLOT index from the two addresses.
For these targets, the canonical PLT entry can just reuse the regular PLT entry (in PltSection).
On PPC32: PltSection (.glink) consists of `b PLTresolve` instructions and `PLTresolve`. The rtld PLT resolver depends on r11 having been set up to the .plt (GotPltSection) entry.
On PPC64 ELFv2: PltSection (.glink) consists of `__glink_PLTresolve` and `bl __glink_PLTresolve`. The rtld PLT resolver depends on r12 having been set up to the .plt (GotPltSection) entry.
We cannot reuse a `b PLTresolve`/`bl __glink_PLTresolve` in PltSection as a canonical PLT entry. PPC64 ELFv2 avoids the problem by using TOC for any external reference, even in non-pic code, so the canonical PLT entry scenario should not happen in the first place.
For PPC32, we have to create a PLT call stub as the canonical PLT entry. The code sequence sets up r11.
Reviewed By: Bdragon28
Differential Revision: https://reviews.llvm.org/D73399
Symbol information can be used to improve out-of-range/misalignment diagnostics.
It also helps R_ARM_CALL/R_ARM_THM_CALL which has different behaviors with different symbol types.
There are many (67) relocateOne() call sites used in thunks, {Arm,AArch64}errata, PLT, etc.
Rename them to `relocateNoSym()` to be clearer that there is no symbol information.
Reviewed By: grimar, peter.smith
Differential Revision: https://reviews.llvm.org/D73254
Summary:
Third part in series to support Safe Whole Program Devirtualization
Enablement, see RFC here:
http://lists.llvm.org/pipermail/llvm-dev/2019-December/137543.html
This patch adds type test metadata under -fwhole-program-vtables,
even for classes without hidden visibility. It then changes WPD to skip
devirtualization for a virtual function call when any of the compatible
vtables has public vcall visibility.
Additionally, internal LLVM options as well as lld and gold-plugin
options are added which enable upgrading all public vcall visibility
to linkage unit (hidden) visibility during LTO. This enables the more
aggressive WPD to kick in based on LTO time knowledge of the visibility
guarantees.
Support was added to all flavors of LTO WPD (regular, hybrid and
index-only), and to both the new and old LTO APIs.
Unfortunately it was not simple to split the first and second parts of
this part of the change (the unconditional emission of type tests and
the upgrading of the vcall visiblity) as I needed a way to upgrade the
public visibility on legacy WPD llvm assembly tests that don't include
linkage unit vcall visibility specifiers, to avoid a lot of test churn.
I also added a mechanism to LowerTypeTests that allows dropping type
test assume sequences we now aggressively insert when we invoke
distributed ThinLTO backends with null indexes, which is used in testing
mode, and which doesn't invoke the normal ThinLTO backend pipeline.
Depends on D71907 and D71911.
Reviewers: pcc, evgeny777, steven_wu, espindola
Subscribers: emaste, Prazek, inglorion, arichardson, hiraditya, MaskRay, dexonsmith, dang, davidxl, cfe-commits, llvm-commits
Tags: #clang, #llvm
Differential Revision: https://reviews.llvm.org/D71913
I felt really sad to push this commit for my selfish purpose to make
glibc -static-pie build with lld. Some code constructs in glibc require
R_X86_64_GOTPCREL/R_X86_64_REX_GOTPCRELX referencing undefined weak to
be resolved to a GOT entry not relocated by R_X86_64_GLOB_DAT (GNU ld
behavior), e.g.
csu/libc-start.c
if (__pthread_initialize_minimal != NULL)
__pthread_initialize_minimal ();
elf/dl-object.c
void
_dl_add_to_namespace_list (struct link_map *new, Lmid_t nsid)
{
/* We modify the list of loaded objects. */
__rtld_lock_lock_recursive (GL(dl_load_write_lock));
Emitting a GLOB_DAT will make the address equal &__ehdr_start (true
value) and cause elf/ldconfig to segfault. glibc really should move away
from weak references, which do not have defined semantics.
Temporarily special case --no-dynamic-linker.
These functions call relocateOne(). This patch is a prerequisite for
making relocateOne() aware of `Symbol` (D73254).
Reviewed By: grimar, nickdesaulniers
Differential Revision: https://reviews.llvm.org/D73250
When annotating a symbol with __declspec(selectany), Clang assigns it
comdat 2 while GCC assigns it comdat 3. This patch enables two object
files that contain a __declspec(selectany) symbol, one created by gcc
and the other by clang, to be linked together instead of issuing a
duplicate symbol error.
Differential Revision: https://reviews.llvm.org/D73139
Summary:
Linker scripts allow filenames to be put in double quotes to prevent
characters in filenames that are part of the linker script syntax from
having their special meaning. Case in point the * wildcard character.
Availability of double quoting filenames also allows to fix a failure in
ELF/linkerscript/filename-spec.s when the path contain a @ which the
lexer consider as a special characters and thus break up a filename
containing it. This may happens under Jenkins which createspath such as
pipeline@2.
To avoid the need for escaping GlobPattern metacharacters in filename
in double quotes, GlobPattern::create is augmented with a new parameter
to request literal matching instead of relying on the presence of a
wildcard character in the pattern.
Reviewers: jhenderson, MaskRay, evgeny777, espindola, alexshap
Reviewed By: MaskRay
Subscribers: peter.smith, grimar, ruiu, emaste, arichardson, hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D72517
The --fix-cortex-a8 is sensitive to alignment and the precise destination
of branch instructions. These are not knowable at relocatable link time. We
follow GNU ld and the --fix-cortex-a53-843419 (D72968) by not patching the
code when there is a relocatable link.
Differential Revision: https://reviews.llvm.org/D73100
Add new method getFirstInputSection and use instead of getInputSections
where appropriate to avoid creation of an unneeded vector of input
sections.
Differential Revision: https://reviews.llvm.org/D73047
The INPUT_SECTION_FLAGS linker script command is used to constrain the
section pattern matching to sections that match certain combinations of
flags.
There are two ways to express the constraint.
withFlags: Section must have these flags.
withoutFlags: Section must not have these flags.
The syntax of the command is:
INPUT_SECTION_FLAGS '(' sect_flag_list ')'
sect_flag_list: NAME
| sect_flag_list '&' NAME
Where NAME matches a section flag name such as SHF_EXECINSTR, or the
integer value of a section flag. If the first character of NAME is ! then
it means must not contain flag.
We do not support the rare case of { INPUT_SECTION_FLAGS(flags) filespec }
where filespec has no input section description like (.text).
As an example from the ld man page:
SECTIONS {
.text : { INPUT_SECTION_FLAGS (SHF_MERGE & SHF_STRINGS) *(.text) }
.text2 : { INPUT_SECTION_FLAGS (!SHF_WRITE) *(.text) }
}
.text will match sections called .text that have both the SHF_MERGE and
SHF_STRINGS flag.
.text2 will match sections called .text that don't have the SHF_WRITE flag.
The flag names accepted are the generic to all targets and SHF_ARM_PURECODE
as it is very useful to filter all the pure code sections into a single
program header that can be marked execute never.
fixes PR44265
Differential Revision: https://reviews.llvm.org/D72756
The test in the origin patch did not create a __debug_str section.
An UBSan check triggered when the corresponding pointer was dereferenced.
Differential Revision: https://reviews.llvm.org/D72695
This reapplies fcc08aa835
which was reverted in b16f82ad3b.
This change broke the UBSan buildbots. More information available in the
original Phabricator review: https://reviews.llvm.org/D72695
This reverts commit fcc08aa835.
Summary:
Unlike R_RISCV_RELAX, which is a linker hint, R_RISCV_ALIGN requires the
support of the linker even when ignoring all R_RISCV_RELAX relocations.
This is because the compiler emits as many NOPs as may be required for
the requested alignment, more than may be required pre-relaxation, to
allow for the target becoming more unaligned after relaxing earlier
sequences. This means that the target is often not initially aligned in
the object files, and so the R_RISCV_ALIGN relocations cannot just be
ignored. Since we do not support linker relaxation, we must turn these
into errors.
Reviewers: ruiu, MaskRay, espindola
Reviewed By: MaskRay
Subscribers: grimar, Jim, emaste, arichardson, asb, rbar, johnrusso, simoncook, sabuasal, niosHD, kito-cheng, shiva0217, zzheng, edward-jones, rogfer01, MartinMosbeck, brucehoult, the_o, rkruppe, PkmX, jocewei, psnobl, benna, lenary, s.egerton, pzheng, sameer.abuasal, apazos, luismarques, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D71820
The code doesn't apply the fix correctly to relocatable links. I could
try to fix the code that applies the fix, but it's pointless: we don't
actually know what the offset will be in the final executable. So just
ignore the flag for relocatable links.
Issue discovered building Android.
Differential Revision: https://reviews.llvm.org/D72968
This change has 2 components:
Target-independent: add a method getDwarfFrameBase to TargetFrameLowering. It
describes how the Dwarf frame base will be encoded. That can be a register (the
default), the CFA (which replaces NVPTX-specific logic in DwarfCompileUnit), or
a DW_OP_WASM_location descriptr.
WebAssembly: Allow WebAssemblyFunctionInfo::getFrameRegister to return the
correct virtual register instead of FP32/SP32 after WebAssemblyReplacePhysRegs
has run. Make WebAssemblyExplicitLocals store the local it allocates for the
frame register. Use this local information to implement getDwarfFrameBase
The result is that the DW_AT_frame_base attribute is correctly encoded for each
subprogram, and each param and local variable has a correct DW_AT_location that
uses DW_OP_fbreg to refer to the frame base.
This is a reland of rG3a05c3969c18 with fixes for the expensive-checks
and Windows builds
Differential Revision: https://reviews.llvm.org/D71681
This essentially reverts b841e119d7.
Such code construct can be used in the following way:
// glibc/stdlib/exit.c
// clang -fuse-ld=lld => succeeded
// clang -fuse-ld=lld -fpie -pie => relocation R_PLT_PC cannot refer to absolute symbol
__attribute__((weak, visibility("hidden"))) extern void __call_tls_dtors();
void __run_exit_handlers() {
if (__call_tls_dtors)
__call_tls_dtors();
}
Since we allow R_PLT_PC in -no-pie mode, it makes sense to allow it in
-pie mode as well.
Reviewed By: pcc
Differential Revision: https://reviews.llvm.org/D72943
In D71281 a fix was put in to round up the size of a ThunkSection to the
nearest 4KiB when performing errata patching. This fixed a problem with a
very large instrumented program that had thunks and patches mutually
trigger each other. Unfortunately it triggers an assertion failure in an
AArch64 allyesconfig build of the kernel. There is a specific assertion
preventing an InputSectionDescription being larger than 4KiB. This will
always trigger if there is at least one Thunk needed in that
InputSectionDescription, which is possible for an allyesconfig build.
Abstractly the problem case is:
.text : {
*(.text) ;
...
. = ALIGN(SZ_4K);
__idmap_text_start = .;
*(.idmap.text)
__idmap_text_end = .;
...
}
The assertion checks that __idmap_text_end - __idmap_start is < 4 KiB.
Note that there is more than one InputSectionDescription in the
OutputSection so we can't just restrict the fix to OutputSections smaller
than 4 KiB.
The fix presented here limits the D71281 to InputSectionDescriptions that
meet the following conditions:
1.) The OutputSection is bigger than the thunkSectionSpacing so adding
thunks will affect the addresses of following code.
2.) The InputSectionDescription is larger than 4 KiB. This will prevent
any assertion failures that an InputSectionDescription is < 4 KiB
in size.
We do this at ThunkSection creation time as at this point we know that
the addresses are stable and up to date prior to adding the thunks as
assignAddresses() will have been called immediately prior to thunk
generation.
The fix reverts the two tests affected by D71281 to their original state
as they no longer need the 4KiB size roundup. I've added simpler tests to
check for D71281 when the OutputSection size is larger than the ThunkSection
spacing.
Fixes https://github.com/ClangBuiltLinux/linux/issues/812
Differential Revision: https://reviews.llvm.org/D72344
When LLVM_APPEND_VC_REV=OFF is set, the current git hash is no
longer embedded into binaries (mostly for --version output).
Without it, most binaries need to relink after every single
commit, even if they didn't change otherwise (due to, say,
a documentation-only commit).
LLVM_APPEND_VC_REV is ON by default, so this doesn't change the
default behavior of anything.
With this, all clients of GenerateVersionFromVCS.cmake honor
LLVM_APPEND_VC_REV.
Differential Revision: https://reviews.llvm.org/D72855
This change has 2 components:
Target-independent: add a method getDwarfFrameBase to TargetFrameLowering. It
describes how the Dwarf frame base will be encoded. That can be a register (the
default), the CFA (which replaces NVPTX-specific logic in DwarfCompileUnit), or
a DW_OP_WASM_location descriptr.
WebAssembly: Allow WebAssemblyFunctionInfo::getFrameRegister to return the
correct virtual register instead of FP32/SP32 after WebAssemblyReplacePhysRegs
has run. Make WebAssemblyExplicitLocals store the local it allocates for the
frame register. Use this local information to implement getDwarfFrameBase
The result is that the DW_AT_frame_base attribute is correctly encoded for each
subprogram, and each param and local variable has a correct DW_AT_location that
uses DW_OP_fbreg to refer to the frame base.
Differential Revision: https://reviews.llvm.org/D71681
`{clang,gcc} -nostdlib -r a.c` passes --dynamic-linker to the linker,
and the expected behavior is to ignore it.
If .interp is kept in the relocatable object file, a final link will get
PT_INTERP even if --dynamic-linker is not specified. glibc ld.so expects
to see PT_DYNAMIC and the executable will likely fail to run.
Ignore --dynamic-linker in -r mode as well as -shared.
ThunkSection contains 4-byte instructions on all targets that use
thunks. Thunks should not be used in any performance sensitive places,
and locality/cache line/instruction fetching arguments should not apply.
We use 16 bytes as preferred function alignments for modern PowerPC cores.
In any case, 8 is not optimal.
Differential Revision: https://reviews.llvm.org/D72819
r354605 moved LLD to the unified revision handling introduced in
rL353268 / r352729 and removed uses of LLD_REPOSITORY_STRING and
LLD_REVISION_STRING.
After this change, we no longer compute the (now-unused) values
of these two variables.
Since this removes the only use of llvm/utils/GetRepositoryPath,
remove that too (it's redundant with the system added in r354605).
While here, also remove LLD_VERSION_MAJOR and LLD_VERSION_MINOR.
Their uses were removed in r285163.
Also remove LLD_VERSION from Version.inc which as far as I can
tell has been unused since the file was added in r219277.
No behavior change.
Differential Revision: https://reviews.llvm.org/D72803
Moved the section name check ahead of any filename matching or
exclusion. Firstly, this reduces the need to retrieve the filename and
secondly, reduces the amount of potentially expensive filename pattern
matching if such rules are present in the linker script.
The impact of this change is particularly significant when linking
objects built with -ffunction-sections and -fstack-size-section, using a
linker script that includes non-trivial filename patterns. In a number
of such cases, the link time is halved.
Differential Revision: https://reviews.llvm.org/D72775
Summary:
This patch could be treated as a rebase of D33960. It also fixes PR35547.
A fix for `llvm/test/Other/close-stderr.ll` is proposed in D68164. Seems
the consensus is that the test is passing by chance and I'm not
sure how important it is for us. So it is removed like in D33960 for now.
The rest of the test fixes are just adding `--crash` flag to `not` tool.
** The reason it fixes PR35547 is
`exit` does cleanup including calling class destructor whereas `abort`
does not do any cleanup. In multithreading environment such as ThinLTO or JIT,
threads may share states which mostly are ManagedStatic<>. If faulting thread
tearing down a class when another thread is using it, there are chances of
memory corruption. This is bad 1. It will stop error reporting like pretty
stack printer; 2. The memory corruption is distracting and nondeterministic in
terms of error message, and corruption type (depending one the timing, it
could be double free, heap free after use, etc.).
Reviewers: rnk, chandlerc, zturner, sepavloff, MaskRay, espindola
Reviewed By: rnk, MaskRay
Subscribers: wuzish, jholewinski, qcolombet, dschuff, jyknight, emaste, sdardis, nemanjai, jvesely, nhaehnle, sbc100, arichardson, jgravelle-google, aheejin, kbarton, fedor.sergeev, asb, rbar, johnrusso, simoncook, apazos, sabuasal, niosHD, jrtc27, zzheng, edward-jones, atanasyan, rogfer01, MartinMosbeck, brucehoult, the_o, PkmX, jocewei, jsji, lenary, s.egerton, pzheng, cfe-commits, MaskRay, filcab, davide, MatzeB, mehdi_amini, hiraditya, steven_wu, dexonsmith, rupprecht, seiya, llvm-commits
Tags: #llvm, #clang
Differential Revision: https://reviews.llvm.org/D67847
This assertion was added as part of D70659 but did not account for .bss
input sections. I noticed that this assert was incorrectly triggering
while building FreeBSD for MIPS64. Fixed by relaxing the assert to also
account for SHT_NOBITS input sections and adjust the test
mips-jalr-non-function.s to link a file with a .bss section first.
Reviewed By: MaskRay, grimar
Differential Revision: https://reviews.llvm.org/D72567
R_HINT is ignored like R_NONE. There are no strong reasons to keep
R_HINT. The largest RelExpr member R_RISCV_PC_INDIRECT is 60 now.
Differential Revision: https://reviews.llvm.org/D71822
Suggested by Peter Collingbourne.
Non-VER_NDX_GLOBAL versions should not be assigned to defined symbols. --exclude-libs violates this and can cause a spurious error "cannot refer to absolute symbol" after D71795.
excludeLibs incorrectly assigns VER_NDX_LOCAL to an undefined weak symbol =>
isPreemptible is false =>
R_PLT_PC is optimized to R_PC =>
in isStaticLinkTimeConstant, an error is emitted.
Reviewed By: pcc, grimar
Differential Revision: https://reviews.llvm.org/D72681
This patch is a joint work by Rui Ueyama and me based on D58102 by Xiang Zhang.
It adds Intel CET (Control-flow Enforcement Technology) support to lld.
The implementation follows the draft version of psABI which you can
download from https://github.com/hjl-tools/x86-psABI/wiki/X86-psABI.
CET introduces a new restriction on indirect jump instructions so that
you can limit the places to which you can jump to using indirect jumps.
In order to use the feature, you need to compile source files with
-fcf-protection=full.
* IBT is enabled if all input files are compiled with the flag. To force enabling ibt, pass -z force-ibt.
* SHSTK is enabled if all input files are compiled with the flag, or if -z shstk is specified.
IBT-enabled executables/shared objects have two PLT sections, ".plt" and
".plt.sec". For the details as to why we have two sections, please read
the comments.
Reviewed By: xiangzhangllvm
Differential Revision: https://reviews.llvm.org/D59780
When compiling position-independent executables, we now use
DW_EH_PE_pcrel | DW_EH_PE_sdata4. However, the MIPS ABI does not define a
64-bit PC-relative ELF relocation so we cannot use sdata8 for the large
code model case. When using the large code model, we fall back to the
previous behaviour of generating absolute relocations.
With this change clang-generated .o files can be linked by LLD without
having to pass -Wl,-z,notext (which creates text relocations).
This is simpler than the approach used by ld.bfd, which rewrites the
.eh_frame section to convert absolute relocations into relative references.
I saw in D13104 that apparently ld.bfd did not accept pc-relative relocations
for MIPS ouput at some point. However, I also checked that recent ld.bfd
can process the clang-generated .o files so this no longer seems true.
Reviewed By: atanasyan
Differential Revision: https://reviews.llvm.org/D72228
For a target symbol defined in the same section, currently we don't emit
a relocation if VariantKind is VK_None (with few exceptions like RISC-V
relaxation), while GNU as emits one. This causes program behavior
differences with and without -ffunction-sections, and can break intended
symbol interposition in a -shared link.
```
.globl foo
foo:
call foo # no relocation. On other targets, may be written as b foo, etc
call bar # a relocation if bar is in another section (e.g. -ffunction-sections)
call foo@plt # a relocation
```
Unify these cases by always emitting a relocation. If we ever want to
optimize `call foo` in -shared links, we should emit a STB_LOCAL alias
and call via the alias.
ARM/thumb2-beq-fixup.s: we now emit a relocation to global_thumb_fn as GNU as does.
X86/Inputs/align-branch-64-2.s: we now emit R_X86_64_PLT32 to foo as GNU does.
ELF/relax.s: rewrite the test as target-in-same-section.s .
We omitted relocations to `global` and now emit R_X86_64_PLT32.
Note, GNU as does not emit a relocation for `jmp global` (maybe its own
bug). Our new behavior is compatible except `jmp global`.
Reviewed By: peter.smith
Differential Revision: https://reviews.llvm.org/D72197
RangeExtensionThunkARM64 is created for out-of-range branches on Windows ARM64
because branch instructions has limited bits to encode target address.
Currently, RangeExtensionThunkARM64 is appended to its referencing COFF section
from object file at link time without any alignment requirement, so if size of
the preceding COFF section is not aligned to instruction boundary (4 bytes),
RangeExtensionThunkARM64 will emit thunk instructions at unaligned address
which is never a valid branch target on ARM64, and usually triggers invalid
instruction exception when branching to it.
This PR fixes it by requiring such thunks to align at 4 bytes.
Differential revision: https://reviews.llvm.org/D72473
RELA targets don't read initial .got.plt entries.
REL targets (ARM, x86-32) write the address of the IFUNC resolver to the
entry (`write32le(buf, s.getVA())`).
The default writeIgotPlt() is not meaningful. Make it a no-op. AArch64
and x86-64 will have 0 as initial .got.plt entries associated with
IFUNC.
Reviewed By: peter.smith
Differential Revision: https://reviews.llvm.org/D72474
Unlike most of our errors in the debug line parser, the "no end of
sequence" message was missing any reference to which line table it
refererred to. This change adds the offset to this message.
Reviewed by: dblaikie
Differential Revision: https://reviews.llvm.org/D72443
Changed ThreadPoolExecutor to no longer use detached threads and instead
to join threads on destruction. This is to prevent intermittent crashing
on Windows when doing a normal full exit, e.g. via exit().
Changed ThreadPoolExecutor to be a ManagedStatic so that it can be
stopped on llvm_shutdown(). Without this, it would only be stopped in
the destructor when doing a full exit. This is required to avoid
intermittent crashing on Windows due to a race condition between the
ThreadPoolExecutor starting up threads and the process doing a fast
exit, e.g. via _exit().
The Windows crashes appear to only occur with the MSVC static runtimes
and are more frequent with the debug static runtime.
These changes also prevent intermittent deadlocks on exit with the MinGW
runtime.
Differential Revision: https://reviews.llvm.org/D70447
down to pass builder in ltobackend.
Currently CodeGenOpts like UnrollLoops/VectorizeLoop/VectorizeSLP in clang
are not passed down to pass builder in ltobackend when new pass manager is
used. This is inconsistent with the behavior when new pass manager is used
and thinlto is not used. Such inconsistency causes slp vectorization pass
not being enabled in ltobackend for O3 + thinlto right now. This patch
fixes that.
Differential Revision: https://reviews.llvm.org/D72386
An undefined weak does not fetch the lazy definition. A lazy weak symbol
should be considered undefined, and thus preemptible if .dynsym exists.
D71795 is not quite an NFC. It errors on an R_X86_64_PLT32 referencing
an undefined weak symbol. isPreemptible is false (incorrect) => R_PLT_PC
is optimized to R_PC => in isStaticLinkTimeConstant, an error is emitted
when an R_PC is applied on an undefined weak (considered absolute).
Weak undefined symbols are preemptible after D71794.
if (sym.isPreemptible)
return false;
if (!config->isPic)
return true;
// isPic means includeInDynsym is true after D71794.
...
// We can delete this if because it can never be true.
if (sym.isUndefWeak)
return true;
Differential Revision: https://reviews.llvm.org/D71795
D59275 added the following clause to Symbol::includeInDynsym()
if (isUndefWeak() && Config->Pie && SharedFiles.empty())
return false;
D59549 explored the possibility to generalize it for -no-pie.
GNU ld's rules are architecture dependent and partly controlled by -z
{,no-}dynamic-undefined-weak. Our attempts to mimic its rules are
actually half-baked and don't provide perceivable benefits (it can save
a few more weak undefined symbols in .dynsym in a -static-pie
executable). Let's just delete the rule for simplicity. We will expect
cosmetic inconsistencies with ld.bfd in certain -static-pie scenarios.
This permits a simplification in D71795.
Reviewed By: peter.smith
Differential Revision: https://reviews.llvm.org/D71794
In AArch64 a branch to an undefined weak symbol that does not have a PLT
entry should resolve to the next instruction. The thunk generation code
can prevent this from happening as a range extension thunk can be generated
if the branch is sufficiently far away from 0, the value of an undefined
weak symbol.
The fix is taken from the Arm implementation of needsThunk(), we prevent a
thunk from being generated to an undefined weak symbol.
fixes pr44451
Differential Revision: https://reviews.llvm.org/D72267
```
lld/ELF/Relocations.cpp:1622:56: warning: loop variable 'ts' of type 'const std::pair<ThunkSection *, uint32_t>' (aka 'const pair<lld:🧝:ThunkSection *, unsigned int>') creates a copy from type 'const std::pair<ThunkSection *, uint32_t>' [-Wrange-loop-analysis]
for (const std::pair<ThunkSection *, uint32_t> ts : isd->thunkSections)
```
Drop const qualifier to fix -Wrange-loop-analysis.
We can make -Wrange-loop-analysis warnings (DiagnoseForRangeConstVariableCopies) on `const A` more
permissive on more types (e.g. POD -> trivially copyable), unfortunately it will not make std::pair
good, because `constexpr pair& operator=(const pair& p);` is unfortunately user-defined.
Reviewed By: Mordante
Differential Revision: https://reviews.llvm.org/D72211
Both MS link.exe and GNU ld.bfd handle it this way; one can have
multiple object files defining the same absolute symbols, as long
as it defines it to the same value. But if there are multiple absolute
symbols with differing values, it is treated as an error.
Differential Revision: https://reviews.llvm.org/D71981
Summary:
I used this information to motivate splitting up the Intrinsic::ID enum
(5d986953c8) and adding a key method to
clang::Sema (586f65d31f) which saved a
fair amount of object file size.
Example output for clang.pdb:
Top 10 types responsible for the most TPI input bytes:
index total bytes count size
0x3890: 8,671,220 = 1,805 * 4,804
0xE13BE: 5,634,720 = 252 * 22,360
0x6874C: 5,181,600 = 408 * 12,700
0x2A1F: 4,520,528 = 1,574 * 2,872
0x64BFF: 4,024,020 = 469 * 8,580
0x1123: 4,012,020 = 2,157 * 1,860
0x6952: 3,753,792 = 912 * 4,116
0xC16F: 3,630,888 = 633 * 5,736
0x69DD: 3,601,160 = 985 * 3,656
0x678D: 3,577,904 = 319 * 11,216
In this case, we can see that record 0x3890 is responsible for ~8MB of
total object file size for objects in clang.
The user can then use llvm-pdbutil to find out what the record is:
$ llvm-pdbutil dump -types -type-index 0x3890
Types (TPI Stream)
============================================================
Showing 1 records.
0x3890 | LF_FIELDLIST [size = 4804]
- LF_STMEMBER [name = `WORDTYPE_MAX`, type = 0x1001, attrs = public]
- LF_MEMBER [name = `U`, Type = 0x37F0, offset = 0, attrs = private]
- LF_MEMBER [name = `BitWidth`, Type = 0x0075 (unsigned), offset = 8, attrs = private]
- LF_METHOD [name = `APInt`, # overloads = 8, overload list = 0x3805]
...
In this case, we can see that these are members of the APInt class,
which is emitted in 1805 object files.
The next largest type is ASTContext:
$ llvm-pdbutil dump -types -type-index 0xE13BE bin/clang.pdb
0xE13BE | LF_FIELDLIST [size = 22360]
- LF_BCLASS
type = 0x653EA, offset = 0, attrs = public
- LF_MEMBER [name = `Types`, Type = 0x653EB, offset = 8, attrs = private]
- LF_MEMBER [name = `ExtQualNodes`, Type = 0x653EC, offset = 24, attrs = private]
- LF_MEMBER [name = `ComplexTypes`, Type = 0x653ED, offset = 48, attrs = private]
- LF_MEMBER [name = `PointerTypes`, Type = 0x653EE, offset = 72, attrs = private]
...
ASTContext only appears 252 times, but the list of members is long, and
must be repeated everywhere it is used.
This was the output before I split Intrinsic::ID:
Top 10 types responsible for the most TPI input:
0x686C: 69,823,920 = 1,070 * 65,256
0x686D: 69,819,640 = 1,070 * 65,252
0x686E: 69,819,640 = 1,070 * 65,252
0x686B: 16,371,000 = 1,070 * 15,300
...
These records were all lists of intrinsic enums.
Reviewers: MaskRay, ruiu
Subscribers: mgrang, zturner, thakis, hans, akhuang, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D71437
Rather than handling zlib handling manually, use `find_package` from CMake
to find zlib properly. Use this to normalize the `LLVM_ENABLE_ZLIB`,
`HAVE_ZLIB`, `HAVE_ZLIB_H`. Furthermore, require zlib if `LLVM_ENABLE_ZLIB` is
set to `YES`, which requires the distributor to explicitly select whether
zlib is enabled or not. This simplifies the CMake handling and usage in
the rest of the tooling.
This restores 68a235d07f,
e6c7ed6d21. The problem with the windows
bot is a need for clearing the cache.
LLD warns if it encounters malformed debug data when parsing line
information for an undefined reference. We only want to warn once.
This patch adds additional checking to make sure the warnings are
printed only once, both for variables within the same program and
variables in later line programs.
Reviewed by: grimar, MaskRay
Differential Revision: https://reviews.llvm.org/D71759
This reverts commit 68a235d07f.
This commit broke the clang-x64-windows-msvc build bot and a follow-up
commit did not fix it. Reverting to fix the bot.
Rather than handling zlib handling manually, use `find_package` from CMake
to find zlib properly. Use this to normalize the `LLVM_ENABLE_ZLIB`,
`HAVE_ZLIB`, `HAVE_ZLIB_H`. Furthermore, require zlib if `LLVM_ENABLE_ZLIB` is
set to `YES`, which requires the distributor to explicitly select whether
zlib is enabled or not. This simplifies the CMake handling and usage in
the rest of the tooling.
One instance looks like a false positive:
lld/ELF/Relocations.cpp:1622:14: note: use reference type 'const std::pair<ThunkSection *, uint32_t> &' (aka 'cons
t pair<lld:🧝:ThunkSection *, unsigned int> &') to prevent copying
for (const std::pair<ThunkSection *, uint32_t> ts : isd->thunkSections)
It is not changed in this commit.
GCC before r245813 (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79439)
did not emit nop after b/bl. This can happen with recursive calls.
r245813 was back ported to GCC 5.5 and GCC 6.4.
This is common, for example, libstdc++.a(locale.o) shipped with GCC 4.9
and many objects in netlib lapack can cause lld to error. gold allows
such calls to the same section. Our __plt_foo symbol's `section` field
is used for ThunkSection, so we can't implement a similar loosen rule
easily. But we can make use of its `file` field which is currently NULL.
Differential Revision: https://reviews.llvm.org/D71639
Similar to D71509 (EM_PPC64), on EM_PPC, the IPLT code sequence should
be similar to a PLT call stub. Unlike EM_PPC64, EM_PPC -msecure-plt has
small/large PIC model differences.
* -fpic/-fpie: R_PPC_PLTREL24 r_addend=0. The call stub loads an address relative to `_GLOBAL_OFFSET_TABLE_`.
* -fPIC/-fPIE: R_PPC_PLTREL24 r_addend=0x8000. (A partial linked object
file may have an addend larger than 0x8000.) The call stub loads an address relative to .got2+0x8000.
Just assume large PIC model for now. This patch makes:
// clang -fuse-ld=lld -msecure-plt -fno-pie -no-pie a.c
// clang -fuse-ld=lld -msecure-plt -fPIE -pie a.c
#include <stdio.h>
static void impl(void) { puts("meow"); }
void thefunc(void) __attribute__((ifunc("resolver")));
void *resolver(void) { return &impl; }
int main(void) {
thefunc();
void (*theptr)(void) = &thefunc;
theptr();
}
work on Linux glibc. -fpie will crash because the compiler and the
linker do not agree on the value which r30 stores (_GLOBAL_OFFSET_TABLE_
vs .got2+0x8000).
Differential Revision: https://reviews.llvm.org/D71621
Non-preemptible IFUNC are placed in in.iplt (.glink on EM_PPC64). If
there is a non-GOT non-PLT relocation, for pointer equality, we change
the type of the symbol from STT_IFUNC and STT_FUNC and bind it to the
.glink entry.
On EM_386, EM_X86_64, EM_ARM, and EM_AARCH64, the PLT code sequence
loads the address from its associated .got.plt slot. An IPLT also has an
associated .got.plt slot and can use the same code sequence.
On EM_PPC64, the PLT code sequence is actually a bl instruction in
.glink . It jumps to `__glink_PLTresolve` (the PLT header). and
`__glink_PLTresolve` computes the .plt slot (relocated by
R_PPC64_JUMP_SLOT).
An IPLT does not have an associated R_PPC64_JUMP_SLOT, so we cannot use
`bl` in .iplt . Instead, create a call stub which has a similar code
sequence as PPC64PltCallStub. We don't save the TOC pointer, so such
scenarios will not work: a function pointer to a non-preemptible ifunc,
which resolves to a function defined in another DSO. This is the
restriction described by https://sourceware.org/glibc/wiki/GNU_IFUNC
(though on many architectures it works in practice):
Requirement (a): Resolver must be defined in the same translation unit as the implementations.
If an ifunc is taken address but not called, technically we don't need
an entry for it, but we currently do that.
This patch makes
// clang -fuse-ld=lld -fno-pie -no-pie a.c
// clang -fuse-ld=lld -fPIE -pie a.c
#include <stdio.h>
static void impl(void) { puts("meow"); }
void thefunc(void) __attribute__((ifunc("resolver")));
void *resolver(void) { return &impl; }
int main(void) {
thefunc();
void (*theptr)(void) = &thefunc;
theptr();
}
work on Linux glibc and FreeBSD. Calling a function pointer pointing to
a Non-preemptible IFUNC never worked before.
Differential Revision: https://reviews.llvm.org/D71509
This restores commit 1417558e4a and its follow-up, reverted by commit c3dbd782f1.
After this commit:
clang -fuse-ld=bfd -no-pie -nostdlib a.c => .interp not created
clang -fuse-ld=bfd -pie -fPIE -nostdlib a.c => .interp created
clang -fuse-ld=gold -no-pie -nostdlib a.c => .interp not created
clang -fuse-ld=gold -pie -fPIE -nostdlib a.c => .interp created
clang -fuse-ld=lld -no-pie -nostdlib a.c => .interp created
clang -fuse-ld=lld -pie -fPIE -nostdlib a.c => .interp created
This reverts commit 1417558e4a.
Also reverts commit 019a92bb28.
This causes check-sanitizer to fail. The "-Nolib" variant of the test
crashes on startup in the loader.
Similar to rL362355, but with the `!config->shared` guard.
(1) {gcc,clang} -fuse-ld=bfd -pie -fPIE -nostdlib a.c => .interp created
(2) {gcc,clang} -fuse-ld=lld -pie -fPIE -nostdlib a.c => .interp not created
(3) {gcc,clang} -fuse-ld=lld -pie -fPIE -nostdlib a.c a.so => .interp created
The inconsistency of (2) is due to the condition `!Config->SharedFiles.empty()`.
To make lld behave more like ld.bfd, we could change the condition to:
config->hasDynSymTab && !config->dynamicLinker.empty() && script->needsInterpSection();
However, that would bring another inconsistency as can be observed with:
(4) {gcc,clang} -fuse-ld=bfd -no-pie -nostdlib a.c => .interp not created
Linux powerpc discards `*(.gnu.version*)` (arch/powerpc/kernel/vmlinux.lds.S)
to suppress --orphan-handling=warn warnings in the -pie output `.tmp_vmlinux1`
The support is simple. Just add isLive() to:
1) Fix an assertion in SectionBase::getPartition() called by VersionTableSection::isNeeded().
2) Suppress DT_VERSYM, DT_VERDEF, DT_VERNEED and DT_VERNEEDNUM, if the relevant section is discarded.
Reviewed By: grimar
Differential Revision: https://reviews.llvm.org/D71819
Fangrui Song