[llvm] 4e3b7df - MC: Introduce R_AARCH64_FUNCINIT64 relocation type.

[via llvm-commits]

Author: Peter Collingbourne
Date: 2025-10-14T10:57:57-07:00
New Revision: 4e3b7df47608c02f3b07845bd414a61a991348a7

URL: https://github.com/llvm/llvm-project/commit/4e3b7df47608c02f3b07845bd414a61a991348a7
DIFF: https://github.com/llvm/llvm-project/commit/4e3b7df47608c02f3b07845bd414a61a991348a7.diff

LOG: MC: Introduce R_AARCH64_FUNCINIT64 relocation type.

R_AARCH64_FUNCINIT64 is a dynamic relocation type for relocating
word-sized data in the output file using the return value of
a function. An R_AARCH64_FUNCINIT64 shall be relocated as an
R_AARCH64_IRELATIVE with the target symbol address if the target
symbol is non-preemptible, and it shall be a usage error to relocate an
R_AARCH64_FUNCINIT64 with a preemptible or STT_GNU_IFUNC target symbol.

The initial use case for this relocation type shall be for emitting
global variable field initializers for structure protection. With
structure protection, the relocation value computation is tied to the
compiler implementation in such a way that it would not be reasonable to
define a relocation type for it (for example, it may involve computing
a hash using a compiler-determined algorithm), hence the need for the
computation to be implemented as code in the binary.

Part of the AArch64 psABI extension:
https://github.com/ARM-software/abi-aa/issues/340

Reviewers: smithp35

Reviewed By: smithp35

Pull Request: https://github.com/llvm/llvm-project/pull/133531

Added: 
    

Modified: 
    llvm/include/llvm/BinaryFormat/ELFRelocs/AArch64.def
    llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
    llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFObjectWriter.cpp
    llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.cpp
    llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.h
    llvm/test/MC/AArch64/data-directive-specifier.s

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/BinaryFormat/ELFRelocs/AArch64.def b/llvm/include/llvm/BinaryFormat/ELFRelocs/AArch64.def
index 8dcc2926e1b59..1cfcdbf67dac5 100644
--- a/llvm/include/llvm/BinaryFormat/ELFRelocs/AArch64.def
+++ b/llvm/include/llvm/BinaryFormat/ELFRelocs/AArch64.def
@@ -62,6 +62,7 @@ ELF_RELOC(R_AARCH64_LD64_GOTPAGE_LO15,               0x139)
 ELF_RELOC(R_AARCH64_PLT32,                           0x13a)
 ELF_RELOC(R_AARCH64_GOTPCREL32,                      0x13b)
 ELF_RELOC(R_AARCH64_PATCHINST,                       0x13c)
+ELF_RELOC(R_AARCH64_FUNCINIT64,                      0x13d)
 // General dynamic TLS relocations
 ELF_RELOC(R_AARCH64_TLSGD_ADR_PREL21,                0x200)
 ELF_RELOC(R_AARCH64_TLSGD_ADR_PAGE21,                0x201)

diff  --git a/llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp b/llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
index 2c3870c6da9b8..636d4f8a9ca3a 100644
--- a/llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
+++ b/llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp
@@ -8217,6 +8217,8 @@ bool AArch64AsmParser::parseDataExpr(const MCExpr *&Res) {
       Spec = AArch64::S_GOTPCREL;
     else if (Identifier == "plt")
       Spec = AArch64::S_PLT;
+    else if (Identifier == "funcinit")
+      Spec = AArch64::S_FUNCINIT;
   }
   if (Spec == AArch64::S_None)
     return Error(Loc, "invalid relocation specifier");

diff  --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFObjectWriter.cpp b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFObjectWriter.cpp
index a388216a95098..892b8da37eb69 100644
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFObjectWriter.cpp
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFObjectWriter.cpp
@@ -232,6 +232,8 @@ unsigned AArch64ELFObjectWriter::getRelocType(const MCFixup &Fixup,
       }
       if (RefKind == AArch64::S_AUTH || RefKind == AArch64::S_AUTHADDR)
         return ELF::R_AARCH64_AUTH_ABS64;
+      if (RefKind == AArch64::S_FUNCINIT)
+        return ELF::R_AARCH64_FUNCINIT64;
       return ELF::R_AARCH64_ABS64;
     }
     case AArch64::fixup_aarch64_add_imm12:

diff  --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.cpp b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.cpp
index 2b5cf3484ffc1..bc090c6157eef 100644
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.cpp
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.cpp
@@ -40,6 +40,7 @@ const MCAsmInfo::AtSpecifier ELFAtSpecifiers[] = {
     {AArch64::S_GOT, "GOT"},
     {AArch64::S_GOTPCREL, "GOTPCREL"},
     {AArch64::S_PLT, "PLT"},
+    {AArch64::S_FUNCINIT, "FUNCINIT"},
 };
 
 const MCAsmInfo::AtSpecifier MachOAtSpecifiers[] = {

diff  --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.h b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.h
index 0dfa61b1dc60e..f2acff54f1665 100644
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.h
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.h
@@ -164,6 +164,7 @@ enum {
   // ELF relocation specifiers in data directives:
   S_PLT          = 0x400,
   S_GOTPCREL,
+  S_FUNCINIT,
 
   // Mach-O @ relocation specifiers:
   S_MACHO_GOT,

diff  --git a/llvm/test/MC/AArch64/data-directive-specifier.s b/llvm/test/MC/AArch64/data-directive-specifier.s
index 2cb7eb3a3ca81..2d1ec4feddfa3 100644
--- a/llvm/test/MC/AArch64/data-directive-specifier.s
+++ b/llvm/test/MC/AArch64/data-directive-specifier.s
@@ -12,6 +12,7 @@ l:
 # CHECK-NEXT:   0x8 R_AARCH64_PLT32 extern 0x4
 # CHECK-NEXT:   0xC R_AARCH64_PLT32 g 0x8
 # CHECK-NEXT:   0x10 R_AARCH64_PLT32 g 0x18
+# CHECK-NEXT:   0x14 R_AARCH64_FUNCINIT64 .text 0x0
 # CHECK-NEXT: }
 .data
 .word l at plt - .
@@ -21,6 +22,8 @@ l:
 .word g at plt - . + 8
 .word g at plt - .data + 8
 
+.quad l at funcinit
+
 # CHECK:      Section ({{.*}}) .rela.data1 {
 # CHECK-NEXT:   0x0 R_AARCH64_GOTPCREL32 data1 0x0
 # CHECK-NEXT:   0x4 R_AARCH64_GOTPCREL32 extern 0x4