An orphan section should be placed in the same memory region as its
anchor section if the latter specifies the memory region explicitly.
If there is no explicit assignment for the anchor section in the linker
script, its memory region is selected by matching attributes, and the
same should be done for the orphan section.
Before the patch, some scripts that were handled smoothly in GNU ld
caused an "error: no memory region specified for section" in lld.
Differential Revision: https://reviews.llvm.org/D112925
This reverts commit 5cbec88cbf.
Vitaly said that 2faac77f26 actually works.
Sanitizer's armv7-linux-androideabi24 configuration has other issues which haven't been identified yet, but that's unrelated to the empty symbol name issue.
If segments are defined in a linker script, placing an orphan section
before the found closest-rank section can result in adding it in a
previous segment and changing flags of that segment. This happens if
the orphan section has a lower sort rank than the found section. To
avoid that, the patch forces orphan sections to be moved after the
found section if segments are explicitly defined.
Differential Revision: https://reviews.llvm.org/D111717
Similar to D69607 but for archive member extraction unrelated to GC. This patch adds --why-extract=.
Prior art:
GNU ld -M prints
```
Archive member included to satisfy reference by file (symbol)
a.a(a.o) main.o (a)
b.a(b.o) (b())
```
-M is mainly for input section/symbol assignment <-> output section mapping
(often huge output) and the information may appear ad-hoc.
Apple ld64
```
__Z1bv forced load of b.a(b.o)
_a forced load of a.a(a.o)
```
It doesn't say the reference file.
Arm's proprietary linker
```
Selecting member vsnprintf.o(c_wfu.l) to define vsnprintf.
...
Loading member vsnprintf.o from c_wfu.l.
definition: vsnprintf
reference : _printf_a
```
---
--why-extract= gives the user the full data (which is much shorter than GNU ld
-Map). It is easy to track a chain of references to one archive member with a
one-liner, e.g.
```
% ld.lld main.o a_b.a b_c.a c.a -o /dev/null --why-extract=- | tee stdout
reference extracted symbol
main.o a_b.a(a_b.o) a
a_b.a(a_b.o) b_c.a(b_c.o) b()
b_c.a(b_c.o) c.a(c.o) c()
% ruby -ane 'BEGIN{p={}}; p[$F[1]]=[$F[0],$F[2]] if $.>1; END{x="c.a(c.o)"; while y=p[x]; puts "#{y[0]} extracts #{x} to resolve #{y[1]}"; x=y[0] end}' stdout
b_c.a(b_c.o) extracts c.a(c.o) to resolve c()
a_b.a(a_b.o) extracts b_c.a(b_c.o) to resolve b()
main.o extracts a_b.a(a_b.o) to resolve a
```
Archive member extraction happens before --gc-sections, so this may not be a live path
under --gc-sections, but I think it is a good approximation in practice.
* Specifying a file avoids output interleaving with --verbose.
* Required `=` prevents accidental overwrite of an input if the user forgets `=`. (Most of compiler drivers' long options accept `=` but not ` `)
Differential Revision: https://reviews.llvm.org/D109572
This is somewhat of a repeat of D66658 but for sections in PT_TLS
segments. Although such sections don't need to be aligned such that
address and offset are congruent modulo the page size, they do need
to be congruent modulo the segment alignment, otherwise the
whole PT_TLS will be unaligned. We therefore use the normal calculation
to determine the section's address within the PT_LOAD rather than
bailing out early due to being SHT_NOBITS.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D106987
Change removeUnusedSyntheticSections() to actually remove empty
SyntheticSections in inputSections.
In addition to doing what removeUnusedSyntheticSections() was meant
to do, this will also make the shuffle-sections tests, which shuffles
inputSections, less sensitive to empty Synthetic Sections that
will not appear in the final image.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D106427
Change-Id: I589eaf596472161a4395fb658aea0fad73318088
`clang -fuse-ld=lld -static-pie -fpie` produced executable
currently crashes and this patch makes it work.
See https://sourceware.org/bugzilla/show_bug.cgi?id=27164
and https://sourceware.org/pipermail/libc-alpha/2021-July/128810.html
While it seems unreasonable to keep csu/libc-start.c ARCH_APPLY_IREL unclear in
static-pie mode and have an unneeded diff -u =(ld.bfd --verbose) =(ld.bfd -pie
--verbose) difference, glibc folks don't want to fix their code.
I feel sad about that but this patch can remove an iffy condition for lld/ELF
as well: `needsInterpSection()`.
There used to be many cases where addends for Elf_Rel were not emitted in
the final object file (mostly when building for MIPS64 since the input .o
files use RELA but the output uses REL). These cases have been fixed since,
but this patch adds a check to ensure that the written values are correct.
It is based on a previous patch that I added to the CHERI fork of LLD since
we were using MIPS64 as a baseline. The work has now almost entirely
shifted to RISC-V and Arm Morello (which use Elf_Rela), but I thought
it would be useful to upstream our local changes anyway.
This patch adds a (hidden) command line flag --check-dynamic-relocations
that can be used to enable these checks. It is also on by default in
assertions builds for targets that handle all dynamic relocations kinds
that LLD can emit in Target::getImplicitAddend(). Currently this is
enabled for ARM, MIPS, and I386.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D101450
This patch changes the DynamicReloc class to store an enum instead
of the overloaded useSymVA member to make it easier to understand
and fix incorrect addends being written in some corner cases. The
change is motivated by a follow-up review that checks the value of
implicit Elf_Rel addends written to the output file.
This patch fixes an incorrect output when using `-z rela` for i386 files
with R_386_GOT32 relocations (not that this really matters since it's an
unsupported configuration).
Storing the relocation expression kind also addresses an incorrect addend
FIXME in ppc64-abs64-dyn.s introduced in D63383.
DynamicReloc now also has a special case for the MIPS TLS relocations
(DynamicReloc::AgainstSymbolWithTargetVA) since the
R_MIPS_TLS_TPREL{32/64} the symbol VA to the GOT for preemptible
symbols. I'm not sure if the symbol value actually should be written
for R_MIPS_TLS_TPREL32, but this patch does not attempt to change
that behaviour.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D100490
During PHDR creation, the case where an output section does not require a
PT_LOAD header but still occupies memory in the current VMA region was not handled.
If such an output section interleaves two output sections that have the same
VMA and LMA regions set, we would previously re-use the existing PT_LOAD header
for the second output section.
However, since the memory region is not contiguous, we need to start a new PT_LOAD
segment.
This fixes https://bugs.llvm.org/show_bug.cgi?id=50558
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D103815
Currently, when reporting unresolved symbols in shared libraries, if an
undefined symbol is firstly seen in a regular object file that shadows
the reference for the same symbol in a shared object. As a result, the
error for the unresolved symbol in the shared library is not reported.
If referencing sections in regular object files are discarded because of
'--gc-sections', no reports about such symbols are generated, and the
linker finishes successfully, generating an output image that fails on
the run.
The patch fixes the issue by keeping symbols, which should be checked,
for each shared library separately.
Differential Revision: https://reviews.llvm.org/D101996
This reuses the approach (and some code) from LLD-ELF.
It's a decent win when linking chromium_framework on a Mac Pro (3.2 GHz 16-Core Intel Xeon W):
N Min Max Median Avg Stddev
x 20 4.58 4.83 4.66 4.6685 0.066591844
+ 20 4.42 4.61 4.5 4.505 0.04751731
Difference at 95.0% confidence
-0.1635 +/- 0.0370242
-3.5022% +/- 0.793064%
(Student's t, pooled s = 0.0578462)
The output binary is 381MB.
Reviewed By: #lld-macho, oontvoo
Differential Revision: https://reviews.llvm.org/D99279
`--shuffle-sections=<seed>` applies to all sections. The new
`--shuffle-sections=<section-glob>=<seed>` makes shuffling selective. To the
best of my knowledge, the option is only used as debugging, so just drop the
original form.
`--shuffle-sections '.init_array*=-1'` `--shuffle-sections '.fini_array*=-1'`.
reverses static constructors/destructors of the same priority.
Useful to detect some static initialization order fiasco.
`--shuffle-sections '.data*=-1'`
reverses `.data*` sections. Useful to detect unfunded pointer comparison results
of two unrelated objects.
If certain sections have an intrinsic order, the old form cannot be used.
Differential Revision: https://reviews.llvm.org/D98679
If the number of sections changes, which is common for re-links after
incremental updates, the section order may change drastically.
Special case -1 to reverse input sections. This is a stable transform.
The section order is more resilient to incremental updates. Usually the
code issue (e.g. Static Initialization Order Fiasco, assuming pointer
comparison result of two unrelated objects) is due to the relative order
between two problematic input files A and B. Checking the regular order
and the reversed order is sufficient.
Differential Revision: https://reviews.llvm.org/D98445
Fixes PR48523. When the linker errors with "output file too large",
one question that comes to mind is how the section sizes differ from
what they were previously. Unfortunately, this information is lost
when the linker exits without writing the output file. This change
makes it so that the error message includes the sizes of the largest
sections.
Reviewed By: MaskRay, grimar, jhenderson
Differential Revision: https://reviews.llvm.org/D94560
We can reduce the number of "using" declarations.
`LLVM_ELF_IMPORT_TYPES_ELFT` was extended in D93801.
Differential revision: https://reviews.llvm.org/D93856
As mentioned in https://reviews.llvm.org/D67479#1667256 ,
* `--[no-]allow-shlib-undefined` control the diagnostic for an unresolved symbol in a shared object
* `-z defs/-z undefs` control the diagnostic for an unresolved symbol in a regular object file
* `--unresolved-symbols=` controls both bits.
In addition, make --warn-unresolved-symbols affect --no-allow-shlib-undefined.
This patch makes the behavior match GNU ld.
Reviewed By: psmith
Differential Revision: https://reviews.llvm.org/D91510
I noticed when running a large link with the --time-trace option that
there were several areas which were missing any specific time trace
categories (aside from the generic link/ExecuteLinker categories). This
patch adds new categories to fill most of the "gaps", or to provide more
detail than was previously provided.
Reviewed by: MaskRay, grimar, russell.gallop
Differential Revision: https://reviews.llvm.org/D90686
In the presence of a gap, the st_value field of a STT_SECTION symbol is the
address of the first input section (incorrect if there is a gap). Set it to the
output section address instead.
In -r mode, this bug can cause an incorrect non-zero st_value of a STT_SECTION
symbol (while output sections have zero addresses, input sections may have
non-zero outSecOff). The non-zero st_value can cause the final link to have
incorrect relocation computation (both GNU ld and LLD add st_value of the
STT_SECTION symbol to the output section address).
Reviewed By: grimar
Differential Revision: https://reviews.llvm.org/D90520
".text.split." holds symbols which are split out from functions in
other input sections. For example, with -fsplit-machine-functions,
placing the cold parts in .text.split instead of .text.unlikely mitigates
against poor profile inaccuracy. Techniques such as hugepage remapping can
make conservative decisions at the section granularity.
Differential Revision: https://reviews.llvm.org/D87840
I have noticed that a 374MiB powerpc64le 'ld.lld' requires 11 passes to link.
There is a ThunkSection (whose parent OutputSection is ".text" of 169MiB) with 12867 thunks.
* GNU ld places non-SHF_ALLOC sections after SHF_ALLOC sections. This has the
advantage that the file offsets of a non-SHF_ALLOC cannot be contained in
a PT_LOAD. This patch matches the behavior.
* For non-SHF_ALLOC non-orphan sections, GNU ld may assign non-zero sh_addr and
treat them similar to SHT_NOBITS (not advance location counter). This
is an alternative approach to what we have done in D85100.
By placing non-SHF_ALLOC sections at the end, we can drop special
cases in createSection and findOrphanPos added by D85100.
Different from GNU ld, we set sh_addr to 0 for non-SHF_ALLOC sections. 0
arguably is better because non-SHF_ALLOC sections don't appear in the memory
image.
ELF spec says:
> sh_addr - If the section will appear in the memory image of a process, this
> member gives the address at which the section's first byte should
> reside. Otherwise, the member contains 0.
D85100 appeared to take a detour. If we take a combined view on D85100 and this
patch, the overall complexity slightly increases (one more 3-line loop) and
compatibility with GNU ld improves.
The behavior we don't want to match is the special treatment of .symtab
.shstrtab .strtab: they can be matched in LLD but not in GNU ld.
Reviewed By: jhenderson, psmith
Differential Revision: https://reviews.llvm.org/D85867
LLD currently does not allow non-contiguous SHF_LINK_ORDER components in an
output section. This makes it infeasible to add SHF_LINK_ORDER to an existing
metadata section if backward compatibility with older object files are
concerned.
We did not allow mixed components (like GNU ld) and D77007 relaxed to allow
non-contiguous SHF_LINK_ORDER components. This patch allows arbitrary mix, with
sorting performed within an InputSectionDescription. For example,
`.rodata : {*(.rodata.foo) *(.rodata.bar)}`, has two InputSectionDescription's.
If there is at least one SHF_LINK_ORDER and at least one non-SHF_LINK_ORDER in
.rodata.foo, they are ordered within `*(.rodata.foo)`: we arbitrarily place
SHF_LINK_ORDER components before non-SHF_LINK_ORDER components (like Solaris ld).
`*(.rodata.bar)` is ordered similarly, but the two InputSectionDescription's
don't interact. It can be argued that this is more reasonable than the previous
behavior where written order was not respected.
It would be nice if the two different semantics (ordering requirement & garbage
collection) were not overloaded on one section flag, however, it is probably
difficult to obtain a generic flag at this point
(https://groups.google.com/forum/#!topic/generic-abi/hgx_m1aXqUo
"SHF_LINK_ORDER's original semantics make upgrade difficult").
(Actually, without the GC semantics, SHF_LINK_ORDER would still have the
sh_link!=0 & sh_link=0 issue. It is just that people find the GC semantics more
useful and tend to use the feature more often.)
GNU ld feature request: https://sourceware.org/bugzilla/show_bug.cgi?id=16833
Differential Revision: https://reviews.llvm.org/D84001
GNU ld allows sections after a non-SHF_ALLOC section to be covered by PT_LOAD
(PR37607) and assigns addresses to non-SHF_ALLOC output sections (similar to
SHF_ALLOC NOBITS sections. The location counter is not advanced).
This patch tries to fix PR37607 (remove a special case in
`Writer<ELFT>::createPhdrs`). To make the created PT_LOAD meaningful, we cannot
reset dot to 0 for a middle non-SHF_ALLOC output section. This results in
removal of two special cases in LinkerScript::assignOffsets. Non-SHF_ALLOC
non-orphan sections can have non-zero addresses like in GNU ld.
The zero address rule for non-SHF_ALLOC sections is weakened to apply to orphan
only. This results in a special case in createSection and findOrphanPos, respectively.
Reviewed By: jhenderson
Differential Revision: https://reviews.llvm.org/D85100
Part of https://bugs.llvm.org/show_bug.cgi?id=41734
The semantics of SHF_LINK_ORDER have been extended to represent metadata
sections associated with some other sections (usually text).
The associated text section may be discarded (e.g. LTO) and we want the
metadata section to have sh_link=0 (D72899, D76802).
Normally the metadata section is only referenced by the associated text
section. sh_link=0 means the associated text section is discarded, and
the metadata section will be garbage collected. If there is another
section (.gc_root) referencing the metadata section, the metadata
section will be retained. It's the .gc_root consumer's job to validate
the metadata sections.
# This creates a SHF_LINK_ORDER .meta with sh_link=0
.section .meta,"awo",@progbits,0
1:
.section .meta,"awo",@progbits,foo
2:
.section .gc_root,"a",@progbits
.quad 1b
.quad 2b
Reviewed By: pcc, jhenderson
Differential Revision: https://reviews.llvm.org/D72904
GNU ld allows sections after a non-SHF_ALLOC section to be covered by PT_LOAD
(PR37607) and assigns addresses to non-SHF_ALLOC output sections (similar to
SHF_ALLOC NOBITS sections. The location counter is not advanced).
This patch tries to fix PR37607 (remove a special case in
`Writer<ELFT>::createPhdrs`). To make the created PT_LOAD meaningful, we cannot
reset dot to 0 for a middle non-SHF_ALLOC output section. This results in
removal of two special cases in LinkerScript::assignOffsets. Non-SHF_ALLOC
non-orphan sections can have non-zero addresses like in GNU ld.
The zero address rule for non-SHF_ALLOC sections is weakened to apply to orphan
only. This results in a special case in createSection and findOrphanPos, respectively.
Reviewed By: jhenderson
Differential Revision: https://reviews.llvm.org/D85100
--oformat=binary is rare (used in a few places in FreeBSD, see `stand/i386/mbr/Makefile` `LDFLAGS_BIN`)
The result should be identical to a normal output transformed by `objcopy -O binary`.
The current implementation ignores addresses and lays out sections by
respecting output section alignments. It can fail when an output section
address is specified, e.g. `.rodata ALIGN(16) :` (PR33651).
Fix PR33651 by respecting LMA. The code is similar to
`tools/llvm-objcop/ELF/Object.cpp` BinaryWriter::finalize after D71035 and D79229.
Unforunately for an output section without PT_LOAD, we assume its LMA is equal
to its VMA. So the result is still incorrect when an output section LMA
(`AT(...)`) is specified
Also drop `alignTo(off, config->wordsize)`. GNU ld does not round up the file size.
Differential Revision: https://reviews.llvm.org/D85086
Fixes PR46348.
ObjFile<ELFT>::initializeSymbols contains two symbol iteration loops:
```
for each symbol
if non-inheriting && non-local
fill in this->symbols[i]
for each symbol
if local
fill in this->symbols[i]
else
symbol resolution
```
Symbol resolution can trigger a duplicate symbol error which will call
InputSectionBase::getObjMsg to iterate over InputFile::symbols. If a
non-local symbol appears after the non-local symbol being resolved
(violating ELF spec), its `this->symbols[i]` entry has not been filled
in, InputSectionBase::getObjMsg will crash due to
`dyn_cast<Defined>(nullptr)`.
To fix the bug, reorganize the two loops to ensure this->symbols is
complete before symbol resolution. This enforces the invariant:
InputFile::symbols has none null entry when InputFile::getSymbols() is called.
```
for each symbol
if non-inheriting
fill in this->symbols[i]
for each symbol starting from firstGlobal
if non-local
symbol resolution
```
Additionally, move the (non-local symbol in local part of .symtab)
diagnostic from Writer<ELFT>::copyLocalSymbols() to initializeSymbols().
Reviewed By: grimar, jhenderson
Differential Revision: https://reviews.llvm.org/D81988
--no-allow-shlib-undefined (enabled by default when linking an
executable) rejects unresolved references in shared objects.
Users may be confused by the common diagnostics of unresolved symbols in
object files (LLD: "undefined symbol: foo"; GNU ld/gold: "undefined reference to")
Learn from GCC/clang " [-Wfoo]": append the option name to the
diagnostics. Users can find relevant information by searching
"--no-allow-shlib-undefined". It should also be obvious to them that
the positive form --allow-shlib-undefined can suppress the error.
Also downgrade the error to a warning if --noinhibit-exec is used (compatible
with GNU ld and gold).
Reviewed By: grimar, psmith
Differential Revision: https://reviews.llvm.org/D81028
In the 64-bit ELF V2 API Specification: Power Architecture, 2.3.3.1. GPR
Save and Restore Functions defines some special functions which may be
referenced by GCC produced assembly (LLVM does not reference them).
With GCC -Os, when the number of call-saved registers exceeds a certain
threshold, GCC generates `_savegpr0_* _restgpr0_*` calls and expects the
linker to define them. See
https://sourceware.org/pipermail/binutils/2002-February/017444.html and
https://sourceware.org/pipermail/binutils/2004-August/036765.html . This
is weird because libgcc.a would be the natural place. However, the linker
generation approach has the advantage that the linker can generate
multiple copies to avoid long branch thunks. We don't consider the
advantage significant enough to complicate our trunk implementation, so
we take a simple approach.
* Check whether `_savegpr0_{14..31}` are used
* If yes, define needed symbols and add an InputSection with the code sequence.
`_savegpr1_*` `_restgpr0_*` and `_restgpr1_*` are similar.
Reviewed By: sfertile
Differential Revision: https://reviews.llvm.org/D79977
For sampleFDO, because the optimized build uses profile generated from previous
release, often we couldn't tell a function without profile was truely cold or
just newly created so we had to treat them conservatively and put them in .text
section instead of .text.unlikely. The result was when we persue the best
performance by locking .text.hot and .text in memory, we wasted a lot of memory
to keep cold functions inside. This problem has been largely solved for regular
sampleFDO using profile-symbol-list (https://reviews.llvm.org/D66374), but for
the case when we use partial profile, we still waste a lot of memory because
of it.
In https://reviews.llvm.org/D62540, we propose to save functions with unknown
hotness information in a special section called ".text.unknown", so that
compiler will treat those functions as luck-warm, but runtime can choose not
to mlock the special section in memory or use other strategy to save memory.
That will solve most of the memory problem even if we use a partial profile.
The patch adds the support in lld for the special section.For sampleFDO,
because the optimized build uses profile generated from previous release,
often we couldn't tell a function without profile was truely cold or just
newly created so we had to treat them conservatively and put them in .text
section instead of .text.unlikely. The result was when we persue the best
performance by locking .text.hot and .text in memory, we wasted a lot of
memory to keep cold functions inside. This problem has been largely solved
for regular sampleFDO using profile-symbol-list
(https://reviews.llvm.org/D66374), but for the case when we use partial
profile, we still waste a lot of memory because of it.
In https://reviews.llvm.org/D62540, we propose to save functions with unknown
hotness information in a special section called ".text.unknown", so that
compiler will treat those functions as luck-warm, but runtime can choose not
to mlock the special section in memory or use other strategy to save memory.
That will solve most of the memory problem even if we use a partial profile.
The patch adds the support in lld for the special section.
Differential Revision: https://reviews.llvm.org/D79590
Essentially takes the lld/Common/Threads.h wrappers and moves them to
the llvm/Support/Paralle.h algorithm header.
The changes are:
- Remove policy parameter, since all clients use `par`.
- Rename the methods to `parallelSort` etc to match LLVM style, since
they are no longer C++17 pstl compatible.
- Move algorithms from llvm::parallel:: to llvm::, since they have
"parallel" in the name and are no longer overloads of the regular
algorithms.
- Add range overloads
- Use the sequential algorithm directly when 1 thread is requested
(skips task grouping)
- Fix the index type of parallelForEachN to size_t. Nobody in LLVM was
using any other parameter, and it made overload resolution hard for
for_each_n(par, 0, foo.size(), ...) because 0 is int, not size_t.
Remove Threads.h and update LLD for that.
This is a prerequisite for parallel public symbol processing in the PDB
library, which is in LLVM.
Reviewed By: MaskRay, aganea
Differential Revision: https://reviews.llvm.org/D79390
Fangrui Song