This change introduces support for zero flag ELF section groups to lld.
lld already supports COMDAT sections, which in ELF are a special type of
ELF section groups. These are generally useful to enable linker GC where
you want a group of sections to always travel together, that is to be
either retained or discarded as a whole, but without the COMDAT
semantics. Other ELF linkers already support zero flag ELF section
groups and this change helps us reach feature parity.
Differential Revision: https://reviews.llvm.org/D96636
When parsing an object file, LLD interleaves undefined symbol resolution (which
may recursively fetch other lazy objects) with defined symbol resolution.
This may lead to surprising results, e.g. if an object file defines currently
undefined symbols and references another lazy symbol, we may interleave defined
symbols with the lazy fetch, potentially leading to the defined symbols
resolving to different files.
As an example, if both `a.a(a.o)` and `a.a(b.o)` define `foo` (not in COMDAT
group, or in different COMDAT groups) and `__profd_foo` (in COMDAT group
`__profd_foo`). LLD may resolve `foo` to `a.a(a.o)` and `__profd_foo` to
`b.a(b.o)`, i.e. different files.
```
parse ArchiveFile a.a
entry fetches a.a(a.o)
parse ObjectFile a.o
define entry
define foo
reference b
b fetches a.a(b.o)
parse ObjectFile b.o
define prevailing __profd_foo
define (ignored) non-prevailing __profd_foo
```
Assuming a set of interconnected symbols are defined all or none in several lazy
objects. Arguably making them resolve to the same file is preferable than making
them resolve to different files (some are lazy objects).
The main argument favoring the new behavior is the stability. The relative order
between a defined symbol and an undefined symbol does not change the symbol
resolution behavior. Only the relative order between two undefined symbols can
affect fetching behaviors.
---
The real world case is reduced from a Fuchsia PGO usage: `a.a(a.o)` has a
constructor within COMDAT group C5 while `a.a(b.o)` has a constructor within
COMDAT group C2. Because they use different group signatures, they are not
de-duplicated. It is not entirely whether Clang behavior is entirely conforming.
LLD selects the PGO counter section (`__profd_*`) from `a.a(b.o)` and the
constructor section from `a.a(a.o)`. The `__profd_*` is a SHF_LINK_ORDER section
linking to its own non-prevailing constructor section, so LLD errors
`sh_link points to discarded section`. This patch fixes the error.
Differential Revision: https://reviews.llvm.org/D95985
`extern const bfd_target aarch64_elf64_le_vec;` is a variable in BFD.
It was somehow misused as an emulation by Android.
```
% aarch64-linux-gnu-ld -m aarch64_elf64_le_vec a.o
aarch64-linux-gnu-ld: unrecognised emulation mode: aarch64_elf64_le_vec
Supported emulations: aarch64linux aarch64elf aarch64elf32 aarch64elf32b aarch64elfb armelf armelfb aarch64linuxb aarch64linux32 aarch64linux32b armelfb_linux_eabi armelf_linux_eabi
```
Acked by Stephen Hines, who removed the flag from Android a while back.
Rewritting the path of the sample profile file in response.txt to be relative to the repro tar.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D96193
A SHF_LINK_ORDER .gcc_except_table is similar to a .gcc_except_table in
a section group. The associated text section is responsible for retaining it.
LLD still does not support GC of non-group non-SHF_LINK_ORDER .gcc_except_table -
but that is not necessary because we can teach the compiler to set SHF_LINK_ORDER.
The current diagnostic has confused users. The new wording is adapted from one suggested by Ian Lance Taylor.
Differential Revision: https://reviews.llvm.org/D95917
binutils 2.36 introduced the new section flag SHF_GNU_RETAIN (for ELFOSABI_GNU &
ELFOSABI_FREEBSD) to mark a sections as a GC root. Several LLVM side toolchain
folks (including me) were involved in the design process of SHF_GNU_RETAIN and
were happy with this proposal.
Currently GNU ld only respects SHF_GNU_RETAIN semantics for ELFOSABI_GNU &
ELFOSABI_FREEBSD object files
(https://sourceware.org/bugzilla/show_bug.cgi?id=27282). GNU ld sets EI_OSABI
to ELFOSABI_GNU for relocatable output
(https://sourceware.org/bugzilla/show_bug.cgi?id=27091). In practice the single
value EI_OSABI is neither a good indicator for object file compatibility, nor a
useful mechanism marking used ELF extensions.
For input, we respect SHF_GNU_RETAIN semantics even for ELFOSABI_NONE object
files. This is compatible with how LLD and GNU ld handle (mildly useful) STT_GNU_IFUNC
/ (emitted by GCC, considered misfeature by some folks) STB_GNU_UNIQUE input.
(As of LLVM 12.0.0, the integrated assembler does not set ELFOSABI_GNU for
STT_GNU_IFUNC/STB_GNU_UNIQUE).
Arguably STT_GNU_IFUNC/STB_GNU_UNIQUE probably need indicators in object files
but SHF_GNU_RETAIN is more likely accepted by more OSABI platforms.
For output, we take a step further than GNU ld: we don't promote ELFOSABI_NONE
to ELFOSABI_GNU for all output.
Differential Revision: https://reviews.llvm.org/D95749
In GCC emitted .debug_info sections, R_386_GOTOFF may be used to
relocate DW_AT_GNU_call_site_value values
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98946).
R_386_GOTOFF (`S + A - GOT`) is one of the `isStaticLinkTimeConstant` relocation
type which is not PC-relative, so it can be used from non-SHF_ALLOC sections. We
current allow new relocation types as needs come. The diagnostic has caught some
bugs in the past.
Differential Revision: https://reviews.llvm.org/D95994
The option catches incompatibility between `R_*_IRELATIVE` and DT_TEXTREL/DF_TEXTREL
before glibc 2.29. Newer glibc versions are more common nowadays and I don't
think this option has ever been used. Diagnosing this problem is also
straightforward by reading the stack trace.
Identify dynamically exported symbols (--export-dynamic[-symbol=],
--dynamic-list=, or definitions needed to preempt shared objects) and
prevent their LTO visibility from being upgraded.
This helps avoid use of whole program devirtualization when there may
be overrides in dynamic libraries.
Differential Revision: https://reviews.llvm.org/D91583
I noticed that this option was not appearing at all in the `--help`
messages for `wasm-ld` or `ld.lld`.
Add help text and make it consistent across all ports.
Differential Revision: https://reviews.llvm.org/D94925
If foo is referenced in any object file, bitcode file or shared object,
`__wrap_foo` should be retained as the redirection target of sym
(f96ff3c0f8).
If the object file defining foo has foo references, we cannot easily distinguish
the case from cases where foo is not referenced (we haven't scanned
relocations). Retain `__wrap_foo` because we choose to wrap sym references
regardless of whether sym is defined to keep non-LTO/LTO/relocatable links' behaviors similar
https://sourceware.org/bugzilla/show_bug.cgi?id=26358 .
If foo is defined in a shared object, `__wrap_foo` can still be omitted
(`wrap-dynamic-undef.s`).
Reviewed By: andrewng
Differential Revision: https://reviews.llvm.org/D95152
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
```
// a.s
jmp fcntl
// b.s
.globl fcntl
fcntl:
ret
```
`ld.lld -shared --wrap=fcntl a.o b.o` has an `R_X86_64_JUMP_SLOT` referencing
the index 0 undefined symbol, which will cause a glibc `symbol lookup error` at
runtime. This is because `__wrap_fcntl` is not in .dynsym
We use an approximation `!wrap->isUndefined()`, which doesn't set
`isUsedInRegularObj` of `__wrap_fcntl` when `fcntl` is referenced and
`__wrap_fcntl` is undefined.
Fix this by using `sym->referenced`.
R_PPC64_ADDR16_HI represents bits 16-31 of a 32-bit value
R_PPC64_ADDR16_HIGH represents bits 16-31 of a 64-bit value.
In the Linux kernel, `LOAD_REG_IMMEDIATE_SYM` defined in `arch/powerpc/include/asm/ppc_asm.h`
uses @l, @high, @higher, @highest to load the 64-bit value of a symbol.
Fixes https://github.com/ClangBuiltLinux/linux/issues/1260
The commit 18aa0be36e changed the default GotBaseSymInGotPlt to true
for AArch64. This is different than binutils, where
_GLOBAL_OFFSET_TABLE_ points at the start or .got.
It seems to not intefere with current relocations used by LLVM. However
as indicated by PR#40357 [1] gcc generates R_AARCH64_LD64_GOTPAGE_LO15
for -pie (in fact it also generated the relocation for -fpic).
This change is requires to correctly handle R_AARCH64_LD64_GOTPAGE_LO15
by lld from objects generated by gcc.
[1] https://bugs.llvm.org/show_bug.cgi?id=40357
OutputSections.h used to close the lld::elf namespace only to
immediately open it again. This change merges both parts into
one.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D94538
Fixes PR48693: --emit-relocs keeps relocation sections. --gdb-index drops
.debug_gnu_pubnames and .debug_gnu_pubtypes but not their relocation sections.
This can cause a null pointer dereference in `getOutputSectionName`.
Also delete debug-gnu-pubnames.s which is covered by gdb-index.s
Reviewed By: grimar
Differential Revision: https://reviews.llvm.org/D94354
Fixes PR48681: after LTO, lto.tmp may reference a libcall symbol not in an IR
symbol table of any bitcode file. If such a symbol is defined in an archive
matched by a --exclude-libs, we don't correctly localize the symbol.
Add another `excludeLibs` after `compileBitcodeFiles` to localize such libcall
symbols. Unfortunately we have keep the existing one for D43126.
Using VER_NDX_LOCAL is an implementation detail of `--exclude-libs`, it does not
necessarily tie to the "localize" behavior. `local:` patterns in a version
script can be omitted.
The `symbol ... has undefined version ...` error should not be exempted.
Ideally we should error as GNU ld does. https://issuetracker.google.com/issues/73020933
Reviewed By: psmith
Differential Revision: https://reviews.llvm.org/D94280
This character indicates that when return pointer authentication is
being used, the function signs the return address using the B key.
Differential Revision: https://reviews.llvm.org/D93954
Add support for linking powerpcle code in LLD.
Rewrite lld/test/ELF/emulation-ppc.s to use a shared check block and add powerpcle tests.
Update tests.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D93917
We can reduce the number of "using" declarations.
`LLVM_ELF_IMPORT_TYPES_ELFT` was extended in D93801.
Differential revision: https://reviews.llvm.org/D93856
For x86-64, D33100 added a diagnostic for local-exec TLS relocations referencing a preemptible symbol.
This patch generalizes it to non-preemptible symbols (see `-Bsymbolic` in `tls.s`)
on all targets.
Local-exec TLS relocations resolve to offsets relative to a fixed point within
the static TLS block, which are only meaningful for the executable.
With this change, `clang -fpic -shared -fuse-ld=bfd a.c` on the following example will be flagged for AArch64/ARM/i386/x86-64/RISC-V
```
static __attribute__((tls_model("local-exec"))) __thread long TlsVar = 42;
long bump() { return ++TlsVar; }
```
Note, in GNU ld, at least arm, riscv and x86's ports have the similar
diagnostics, but aarch64 and ppc64 do not error.
Differential Revision: https://reviews.llvm.org/D93331
Alternative to D91611.
The TLS General Dynamic/Local Dynamic code sequences need to mark
`__tls_get_addr` with R_PPC64_TLSGD or R_PPC64_TLSLD, e.g.
```
addis r3, r2, x@got@tlsgd@ha # R_PPC64_GOT_TLSGD16_HA
addi r3, r3, x@got@tlsgd@l # R_PPC64_GOT_TLSGD16_LO
bl __tls_get_addr(x@tlsgd) # R_PPC64_TLSGD followed by R_PPC64_REL24
nop
```
However, there are two deviations form the above:
1. direct call to `__tls_get_addr`. This is essential to implement ld.so in glibc/musl/FreeBSD.
```
bl __tls_get_addr
nop
```
This is only used in a -shared link, and thus not subject to the GD/LD to IE/LE
relaxation issue below.
2. Missing R_PPC64_TLSGD/R_PPC64_TLSGD for compiler generated TLS references
According to Stefan Pintille, "In the early days of the transition from the
ELFv1 ABI that is used for big endian PowerPC Linux distributions to the ELFv2
ABI that is used for little endian PowerPC Linux distributions, there was some
ambiguity in the specification of the relocations for TLS. The GNU linker has
implemented support for correct handling of calls to __tls_get_addr with a
missing relocation. Unfortunately, we didn't notice that the IBM XL compiler
did not handle TLS according to the updated ABI until we tried linking XL
compiled libraries with LLD."
In short, LLD needs to work around the old IBM XL compiler issue.
Otherwise, if the object file is linked in -no-pie or -pie mode,
the result will be incorrect because the 4 instructions are partially
rewritten (the latter 2 are not changed).
Work around the compiler bug by disable General Dynamic/Local Dynamic to
Initial Exec/Local Exec relaxation. Note, we also disable Initial Exec
to Local Exec relaxation for implementation simplicity, though technically it can be kept.
ppc64-tls-missing-gdld.s demonstrates the updated behavior.
Reviewed By: #powerpc, stefanp, grimar
Differential Revision: https://reviews.llvm.org/D92959
The scope of R_TLS (TP offset relocation types (TPREL/TPOFF) used for the
local-exec TLS model) is actually narrower than its name may imply. R_TLS_NEG
is only used by Solaris R_386_TLS_LE_32.
Rename them so that they will be less confusing.
Reviewed By: grimar, psmith, rprichard
Differential Revision: https://reviews.llvm.org/D93467
Libraries linked to the lld elf library exposes a function named main.
When debugging code linked to such libraries and intending to set a
breakpoint at main, the debugger also sets breakpoint at the main
function at lld elf driver. The possible choice was to rename it to
link but that would again clash with lld::*::link. This patch tries
to consistently rename them to linkerMain.
Differential Revision: https://reviews.llvm.org/D91418
As indicated by AArch64 ELF specification, symbols with st_other
marked with STO_AARCH64_VARIANT_PCS indicates it may follow a variant
procedure call standard with different register usage convention
(for instance SVE calls).
Static linkers must preserve the marking and propagate it to the dynamic
symbol table if any reference or definition of the symbol is marked with
STO_AARCH64_VARIANT_PCS, and add a DT_AARCH64_VARIANT_PCS dynamic tag if
there are R_<CLS>_JUMP_SLOT relocations that reference that symbols.
It implements https://bugs.llvm.org/show_bug.cgi?id=48368.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D93045
Fix PR48357: If .rela.dyn appears as an output section description, its type may
be SHT_RELA (due to the empty synthetic .rela.plt) while there is no input
section. The empty .rela.dyn may be retained due to a reference in a linker
script. Don't crash.
Reviewed By: grimar
Differential Revision: https://reviews.llvm.org/D93367
Follow the naming set by TI's own GCC-based toolchain.
Also, force the `osabi` field to `ELFOSABI_STANDALONE`, this matches GNU LD's output (the patching is done in `elf32_msp430_post_process_headers`).
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D92931
Normally we should not delete options. However, the Clang driver passes
`-plugin-opt={new,legacy}-pass-manager` instead of
`--[no-]lto-legacy-pass-manager` (`-plugin-opt=new-pass-manager` has been used
since 7.0), and it is unlikely anyone will use the `--lto-*` style options directly.
So let's rename them to be consistent with the Clang driver option names.
Reviewed By: aeubanks
Differential Revision: https://reviews.llvm.org/D92988
-DENABLE_EXPERIMENTAL_NEW_PASS_MANAGER=on configured LLD and LLVMgold.so
will use the new pass manager by default. Add an option to
use the legacy pass manager. This will also be used by the Clang driver
when -fno-new-pass-manager (D92915) / -fno-experimental-new-pass-manager is set.
Reviewed By: aeubanks, tejohnson
Differential Revision: https://reviews.llvm.org/D92916
This patch changes the archive handling to enable the semantics needed
for legacy FORTRAN common blocks and block data. When we have a COMMON
definition of a symbol and are including an archive, LLD will now
search the members for global/weak defintions to override the COMMON
symbol. The previous LLD behavior (where a member would only be included
if it satisifed some other needed symbol definition) can be re-enabled with the
option '-no-fortran-common'.
Differential Revision: https://reviews.llvm.org/D86142
This reverts a side effect introduced in the code cleanup patch D43571:
LLD started to emit empty output sections that are explicitly assigned to a segment.
This patch fixes the issue by removing the !sec.phdrs.empty() special case from
isDiscardable. As compensation, we add an early phdrs propagation step (see the inline comment).
This is similar to one that we do in adjustSectionsAfterSorting.
Differential revision: https://reviews.llvm.org/D92301
Also, for .o files, include full path as given on link command line.
Before:
lld: error: undefined symbol [...], referenced from sandbox_logging.o
After:
lld: error: undefined symbol [...], referenced from libseatbelt.a(sandbox_logging.o)
Move archiveName up to InputFile so we can consistently use toString()
to print InputFiles in diags, and pass it to the ObjFile ctor. This
matches the ELF and COFF ports.
Differential Revision: https://reviews.llvm.org/D92437
If an object file has an undefined foo@v1, we emit a dynamic symbol foo.
This is incorrect if at runtime a shared object provides the non-default version foo@v1
(the undefined foo may bind to foo@@v2, for example).
GNU ld issues an error for this case, even if foo@v1 is undefined weak
(https://sourceware.org/bugzilla/show_bug.cgi?id=3351). This behavior makes
sense because to represent an undefined foo@v1, we have to construct a Verneed
entry. However, without knowing the defining filename, we cannot construct a
Verneed entry (Verneed::vn_file is unavailable).
This patch implements the error.
Depends on D92258
Reviewed By: grimar
Differential Revision: https://reviews.llvm.org/D92260
Nico Weber