And introduce MCValue::getAddSym & MCValue::getSubSym to simplify code.
We do not utilize the MCSymbol argument of needsRelocateWithSymbol
as it will go away in the future.
It's the decision of backend needsRelocateWithSymbol whether the
STT_SECTION adjustment should be suppressed.
test/MC/AArch64/data-directive-specifier.s demonstrates how to test this
property.
Finish the migration started by
eea7d32bd262bb5f61790c42ebaa147aa26c3979.
STT_TLS setting has been moved to backend getRelocType.
75f5a4f0dc7d96134cca86543ef3f86ef218ce77 migrated the last target, VE.
Similar to previous migration done for other targets (PowerPC, X86, ARM,
etc). Switch from the confusing VariantKind to Specifier, which aligns
with Arm and IBM AIX's documentation.
In addition, rename *MCExpr::getKind, which confusingly shadows the base class getKind.
In the future, relocation specifiers should be encoded as part of
SystemZMCExpr instead of MCSymbolRefExpr.
Move target-specific members outside of MCSymbolRefExpr::VariantKind
(a legacy interface I am eliminating). Most changes are mechanic,
except:
* ELFObjectWriter::shouldRelocateWithSymbol
* The legacy generic code uses `ELFObjectWriter::fixSymbolsInTLSFixups`
to set `STT_TLS` (and use an unnecessary expression walk). The better
way is to do this in `getRelocType`, which I have done for
AArch64, PowerPC, and RISC-V.
In the future, we should encode expressions with a relocation specifier
as X86MCExpr and use MCValue::RefKind to hold the specifier of the
relocatable expression.
https://maskray.me/blog/2025-03-16-relocation-generation-in-assemblers
While here, rename "Modifier' to "Specifier":
> "Relocation modifier", though concise, suggests adjustments happen during the linker's relocation step rather than the assembler's expression evaluation. I landed on "relocation specifier" as the winner. It's clear, aligns with Arm and IBM’s usage, and fits the assembler's role seamlessly.
Pull Request: https://github.com/llvm/llvm-project/pull/132149
Most changes are mechanic, except:
* ELFObjectWriter::shouldRelocateWithSymbol: .TOC.@tocbase does not
register the undefined symbol. Move the handling into the
Sym->isUndefined() code path.
* ELFObjectWriter::fixSymbolsInTLSFixups's VK_PPC* cases are moved to
PPCELFObjectWriter::getRelocType. We should do similar refactoring
for other targets and eventually remove fixSymbolsInTLSFixups.
In the future, we should classify PPCMCExpr similar to AArch64MCExpr.
so that we only need to do it once during recordRelocation. In the
future, we should change fixSymbolsInTLSFixups to apply to MCValue
instead of MCExpr, similar to GNU assembler.
The o32 ABI specifies:
> Each relocation type of R_MIPS_HI16 must have an associated R_MIPS_LO16 entry immediately following it in the list of relocations. [...] the addend AHL is computed as (AHI << 16) + (short)ALO
In practice, the high-part and low-part relocations may not be adjacent
in assembly files, requiring the assembler to reorder relocations.
http://reviews.llvm.org/D19718 performed the reordering, but did not
optimize for the common case where a %lo immediately follows its
matching %hi. The quadratic time complexity could make sections with
many relocations very slow to process.
This patch implements the fast path, simplifies the code, and makes the
behavior more similar to GNU assembler (for the .rel.mips_hilo_8b test).
We also remove `OriginalSymbol`, removing overhead for other targets.
Fix#104562
Pull Request: https://github.com/llvm/llvm-project/pull/104723
For MIPS's o32 ABI (REL), https://reviews.llvm.org/D19718 introduced
`OriginalAddend` to find the matching R_MIPS_LO16 relocation for
R_MIPS_GOT16 when STT_SECTION conversion is applicable.
lw $2, %lo(local1)
lui $2, %got(local1)
However, we could just store the original `Addend` in
`ELFRelocationEntry` and remove `OriginalAddend`.
Note: The relocation ordering algorithm in
https://reviews.llvm.org/D19718 is inefficient (#104562), which will be
addressed by another patch.
Useful with other infrastructure that consume LLVM statistics to get an
idea of distribution of section sizes.
The breakdown of various section types is subject to change, this is
just an initial go at gather some sort of stats.
Example stats compiling X86ISelLowering.cpp (-g1):
```
"elf-object-writer.AllocROBytes": 308268,
"elf-object-writer.AllocRWBytes": 6240,
"elf-object-writer.AllocTextBytes": 1659203,
"elf-object-writer.DebugBytes": 3180386,
"elf-object-writer.OtherBytes": 5862,
"elf-object-writer.RelocationBytes": 2623440,
"elf-object-writer.StrtabBytes": 228599,
"elf-object-writer.SymtabBytes": 120336,
"elf-object-writer.UnwindBytes": 85216,
```
Similar to commit 28fcafb50274be2520117eacb0a886adafefe59d (2011) for
MachObjectWriter and commit 9539a7796094ff5fb59d9c685140ea2e214b945c for
WinCOFFObjectWriter.
MCELFStreamer can now access ELFObjectWriter directly without adding
ELF-specific markGnuAbi (https://reviews.llvm.org/D97976) and
setOverrideABIVersion to MCObjectWriter.
A few member variables have to be made public since we cannot use a
friend declaration for ELFWriter.
Remove some maps. Mostly cleanup, only a slight performance win.
- Replace SectionIndexMap with layout order: The section layout order is
only used in MachO, so we can repurpose the field as section table
index.
- Store section offsets in MCSectionELF: No need for a map, and
especially not a std::map. Direct access to the underlying (and easily
modifyable) data structure is always faster.
- Improve storage of groups: There's no point in having a DenseMap, the
number of sections and groups are reasonably small to use vectors.
CREL is a compact relocation format for the ELF object file format.
This patch adds integrated assembler support (using the RELA form)
available with `llvm-mc -filetype=obj -crel a.s -o a.o`.
A dependent patch will add `clang -c -Wa,--crel,--allow-experimental-crel`.
Also add llvm-readobj support (for both REL and RELA forms) to
facilitate testing the assembler. Additionally, yaml2obj gains support
for the RELA form to aid testing with llvm-readobj.
We temporarily assign the section type code 0x40000020 from the generic
range to `SHT_CREL`. We avoided using `SHT_LLVM_` or `SHT_GNU_` to
avoid code churn and maintain broader applicability for interested psABIs.
Similarly, `DT_CREL` is temporarily 0x40000026.
LLVM will change the code and break compatibility. This is not an issue
if all relocatable files using CREL are regenerated (aka no prebuilt
relocatable files).
Link: https://discourse.llvm.org/t/rfc-crel-a-compact-relocation-format-for-elf/77600
Pull Request: https://github.com/llvm/llvm-project/pull/91280
Follow-up to 10c894cffd0f4bef21b54a43b5780240532e44cf.
MCAsmLayout, introduced by ac8a95498a99eb16dff9d3d0186616645d200b6e
(2010), provides APIs to compute fragment/symbol/section offsets.
The separate class is cumbersome and passing it around has overhead.
Let's remove it as the underlying implementation is tightly coupled with
MCAsmLayout anyway.
Some forwarders are added to ease migration.
Follow-up to https://reviews.llvm.org/D128958
* Move target-specific code away from the generic ELFWriter.
* All sections should have been created before MCAssembler::layout.
* Remove one `registerSection` use, which should be considered private to MCAssembler.
Follow-up to https://reviews.llvm.org/D128958
* Move target-specific code away from the generic ELFWriter.
* All sections should have been created before MCAssembler::layout.
* Remove one `registerSection` use, which should be considered private to MCAssembler.
Temporary symbols generated for .eh_frame and .debug_line have an empty
name, which appear in .symtab in the presence of RISC-V style linker
relaxation and will not be discarded by ld/objcopy --discard-locals
(-X).
In contrast, GNU assembler's riscv port assigns a fake name ".L0 " (with
a trailing space) to these symbols so that will be discarded by
ld/objcopy --discard-locals.
This patch matches the GNU behavior. Since Clang's RISC-V targets pass
-X to ld, and GNU ld defaults to -X for RISC-V targets, these ".L0 "
symbols will be discarded after linking by default, as expected by
users.
The llvm-symbolizer special case for RISC-V `SF_FormatSpecific` symbols
https://reviews.llvm.org/D98669 needs to be adjusted.
Note: `"":` in assembly currently crashes.
Note: bolt tests used /usr/bin/clang before
llvmorg-19-init-9532-g59bfc3106874.
The revert llvmorg-19-init-9531-g28b55342e1a8 actually broke
bolt/test/RISCV/fake-label-no-entry.c
Temporary symbols generated for .eh_frame and .debug_line have an empty
name, which appear in .symtab in the presence of RISC-V style linker
relaxation and will not be discarded by ld/objcopy --discard-locals
(-X).
In contrast, GNU assembler's riscv port assigns a fake name ".L0 " (with
a trailing space) to these symbols so that will be discarded by
ld/objcopy --discard-locals.
This patch matches the GNU behavior. Since Clang's RISC-V targets pass
-X to ld, and GNU ld defaults to -X for RISC-V targets, these ".L0 "
symbols will be discarded after linking by default, as expected by
users.
The llvm-symbolizer special case for RISC-V `SF_FormatSpecific` symbols
https://reviews.llvm.org/D98669 needs to be adjusted.
Note: `"":` in assembly currently crashes.
Temporary symbols generated for .eh_frame and .debug_line have an empty
name, which appear in .symtab in the presence of RISC-V style linker
relaxation and will not be discarded by ld/objcopy --discard-locals
(-X).
In contrast, GNU assembler's riscv port assigns a fake name ".L0 " (with
a trailing space) to these symbols so that will be discarded by
ld/objcopy --discard-locals.
This patch matches the GNU behavior. Since Clang's RISC-V targets pass
-X to ld, and GNU ld defaults to -X for RISC-V targets, these ".L0 "
symbols will be discarded after linking by default, as expected by
users.
The llvm-symbolizer special case for RISC-V `SF_FormatSpecific` symbols
https://reviews.llvm.org/D98669 needs to be adjusted.
Note: `"":` in assembly currently crashes.
And fix `if (hasRelocationAddend())` to `usesRela` to properly treat
SHT_LLVM_CALL_GRAPH_PROFILE as SHT_REL. The incorrect does not cause a
problem because the synthesized SHT_LLVM_CALL_GRAPH_PROFILE has zero
addends.
