ELF: Add support for R_AARCH64_INST32 relocation.

The R_AARCH64_INST32 relocation type is to support deactivation
symbols. For more information, see the RFC:
https://discourse.llvm.org/t/rfc-deactivation-symbols/85556

TODO:
- Agree on semantics and relocation type number.
- Add tests.

Pull Request: llvm#133534

Author: pcc

lld/ELF/Arch/AArch64.cpp

@@ -135,6 +135,7 @@ RelExpr AArch64::getRelExpr(RelType type, const Symbol &s,
   switch (type) {
   case R_AARCH64_ABS16:
   case R_AARCH64_ABS32:
+  case R_AARCH64_INST32:
   case R_AARCH64_ABS64:
   case R_AARCH64_ADD_ABS_LO12_NC:
   case R_AARCH64_LDST128_ABS_LO12_NC:
@@ -278,6 +279,7 @@ int64_t AArch64::getImplicitAddend(const uint8_t *buf, RelType type) const {
   case R_AARCH64_PREL16:
     return SignExtend64<16>(read16(ctx, buf));
   case R_AARCH64_ABS32:
+  case R_AARCH64_INST32:
   case R_AARCH64_PREL32:
     return SignExtend64<32>(read32(ctx, buf));
   case R_AARCH64_ABS64:
@@ -505,6 +507,12 @@ void AArch64::relocate(uint8_t *loc, const Relocation &rel,
     checkIntUInt(ctx, loc, val, 32, rel);
     write32(ctx, loc, val);
     break;
+  case R_AARCH64_INST32:
+    if (!rel.sym->isUndefined()) {
+      checkIntUInt(ctx, loc, val, 32, rel);
+      write32(ctx, loc, val);
+    }
+    break;
   case R_AARCH64_PLT32:
   case R_AARCH64_GOTPCREL32:
     checkInt(ctx, loc, val, 32, rel);

llvm/include/llvm/BinaryFormat/ELFRelocs/AArch64.def

@@ -61,6 +61,7 @@ ELF_RELOC(R_AARCH64_LD64_GOT_LO12_NC,                0x138)
 ELF_RELOC(R_AARCH64_LD64_GOTPAGE_LO15,               0x139)
 ELF_RELOC(R_AARCH64_PLT32,                           0x13a)
 ELF_RELOC(R_AARCH64_GOTPCREL32,                      0x13b)
+ELF_RELOC(R_AARCH64_INST32,                          0x13c)
 // General dynamic TLS relocations
 ELF_RELOC(R_AARCH64_TLSGD_ADR_PREL21,                0x200)
 ELF_RELOC(R_AARCH64_TLSGD_ADR_PAGE21,                0x201)