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:
ARM-software/abi-aa#340

Reviewers: smithp35

Reviewed By: smithp35

Pull Request: #133531

Author: pcc

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)

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");

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:

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[] = {

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,

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@plt - .
@@ -21,6 +22,8 @@ l:
 .word g@plt - . + 8
 .word g@plt - .data + 8
 
+.quad l@funcinit
+
 # CHECK:      Section ({{.*}}) .rela.data1 {
 # CHECK-NEXT:   0x0 R_AARCH64_GOTPCREL32 data1 0x0
 # CHECK-NEXT:   0x4 R_AARCH64_GOTPCREL32 extern 0x4