[llvm] [X86][MC] Support R_X86_64_CODE_4_GOTPC32_TLSDESC (PR #116908)
via llvm-commits
llvm-commits at lists.llvm.org
Tue Nov 19 19:08:21 PST 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-binary-utilities
Author: Feng Zou (fzou1)
<details>
<summary>Changes</summary>
For
lea name@<!-- -->tlsdesc(%rip), %reg
add
R_X86_64_CODE_4_GOTPC32_TLSDESC = 45
if the instruction starts at 4 bytes before the relocation offset. This should be used if reg is one of the additional general-purpose registers, r16-r31, in Intel APX. It is similar to R_X86_64_GOTPC32_TLSDESC and linker optimization must take the different instruction encoding into account.
Linker can convert the instructions with R_X86_64_CODE_4_GOTPC32_TLSDESC to
mov $name@<!-- -->tpoff, %reg
if the first byte of the instruction at the relocation offset - 4 is 0xd5 (namely, encoded w/REX2 prefix) when possible.
Binutils patch: https://github.com/bminor/binutils-gdb/commit/a533c8df598b5ef99c54a13e2b137c98b34b043c
Binutils mailthread: https://sourceware.org/pipermail/binutils/2023-December/131463.html
ABI discussion: https://groups.google.com/g/x86-64-abi/c/ACwD-UQXVDs/m/vrgTenKyFwAJ
Blog: https://kanrobert.github.io/rfc/All-about-APX-relocation
---
Full diff: https://github.com/llvm/llvm-project/pull/116908.diff
4 Files Affected:
- (modified) llvm/include/llvm/BinaryFormat/ELFRelocs/x86_64.def (+1)
- (modified) llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp (+2)
- (modified) llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp (+1)
- (modified) llvm/test/MC/X86/tlsdesc-64.s (+12)
``````````diff
diff --git a/llvm/include/llvm/BinaryFormat/ELFRelocs/x86_64.def b/llvm/include/llvm/BinaryFormat/ELFRelocs/x86_64.def
index 161b1969abfeb4..1008263b3213ec 100644
--- a/llvm/include/llvm/BinaryFormat/ELFRelocs/x86_64.def
+++ b/llvm/include/llvm/BinaryFormat/ELFRelocs/x86_64.def
@@ -44,3 +44,4 @@ ELF_RELOC(R_X86_64_IRELATIVE, 37)
ELF_RELOC(R_X86_64_GOTPCRELX, 41)
ELF_RELOC(R_X86_64_REX_GOTPCRELX, 42)
ELF_RELOC(R_X86_64_REX2_GOTPCRELX, 43)
+ELF_RELOC(R_X86_64_CODE_4_GOTPC32_TLSDESC, 45)
\ No newline at end of file
diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
index 90222278d1ad6f..f0a7cc7c263e55 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
@@ -191,6 +191,8 @@ static unsigned getRelocType64(MCContext &Ctx, SMLoc Loc,
case MCSymbolRefExpr::VK_TLSCALL:
return ELF::R_X86_64_TLSDESC_CALL;
case MCSymbolRefExpr::VK_TLSDESC:
+ if ((unsigned)Kind == X86::reloc_riprel_4byte_relax_rex2)
+ return ELF::R_X86_64_CODE_4_GOTPC32_TLSDESC;
return ELF::R_X86_64_GOTPC32_TLSDESC;
case MCSymbolRefExpr::VK_TLSGD:
checkIs32(Ctx, Loc, Type);
diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
index 206436191c2584..510fc9fc417f2f 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
@@ -666,6 +666,7 @@ void X86MCCodeEmitter::emitMemModRMByte(
case X86::SBB64rm:
case X86::SUB64rm:
case X86::XOR64rm:
+ case X86::LEA64r:
return Kind == REX2 ? X86::reloc_riprel_4byte_relax_rex2
: Kind == REX ? X86::reloc_riprel_4byte_relax_rex
: X86::reloc_riprel_4byte_relax;
diff --git a/llvm/test/MC/X86/tlsdesc-64.s b/llvm/test/MC/X86/tlsdesc-64.s
index ebe1710c3e869b..93e0f2bda0691d 100644
--- a/llvm/test/MC/X86/tlsdesc-64.s
+++ b/llvm/test/MC/X86/tlsdesc-64.s
@@ -17,3 +17,15 @@
leaq a at tlsdesc(%rip), %rax
call *a at tlscall(%rax)
addq %fs:0, %rax
+
+# PRINT: leaq a at tlsdesc(%rip), %r16
+# PRINT-NEXT: callq *a at tlscall(%r16)
+
+# CHECK: 12: leaq (%rip), %r16 # 0x1a <{{.*}}>
+# CHECK-NEXT: 0000000000000016: R_X86_64_CODE_4_GOTPC32_TLSDESC a-0x4
+# CHECK-NEXT: 1a: callq *(%r16)
+# CHECK-NEXT: 000000000000001a: R_X86_64_TLSDESC_CALL a
+
+leaq a at tlsdesc(%rip), %r16
+call *a at tlscall(%r16)
+addq %fs:0, %r16
\ No newline at end of file
``````````
</details>
https://github.com/llvm/llvm-project/pull/116908
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