[llvm][lld] Support R_<CLS>_GOTREL32

This is the follopw implementation to
ARM-software/abi-aa#223 that supports this
relocation in llvm and lld.

Author: PiJoules

lld/ELF/Arch/AArch64.cpp

@@ -165,6 +165,8 @@ RelExpr AArch64::getRelExpr(RelType type, const Symbol &s,
   case R_AARCH64_ADR_GOT_PAGE:
   case R_AARCH64_TLSIE_ADR_GOTTPREL_PAGE21:
     return R_AARCH64_GOT_PAGE_PC;
+  case R_AARCH64_GOTPCREL32:
+    return R_GOT_PC;
   case R_AARCH64_NONE:
     return R_NONE;
   default:
@@ -374,6 +376,7 @@ void AArch64::relocate(uint8_t *loc, const Relocation &rel,
     write32(loc, val);
     break;
   case R_AARCH64_PLT32:
+  case R_AARCH64_GOTPCREL32:
     checkInt(loc, val, 32, rel);
     write32(loc, val);
     break;

lld/test/ELF/aarch64-reloc-gotpcrel32.s

@@ -0,0 +1,27 @@
+// REQUIRES: aarch64
+// RUN: llvm-mc -filetype=obj -triple=aarch64 %s -o %t.o
+// RUN: ld.lld %t.o -o %t.so -shared --noinhibit-exec 2>&1 | FileCheck %s --check-prefix=WARN
+// RUN: llvm-readelf -S %t.so | FileCheck --check-prefix=SEC %s
+// RUN: llvm-objdump --no-print-imm-hex -s -d %t.so | FileCheck %s
+
+// SEC: .got PROGBITS 0000000000020390
+
+  .section .data
+  .globl bar
+bar:
+
+  .globl _start
+_start:  // PC = 0x303a0
+// bar@GOTPCREL   = 0x20390 (got entry for `bar`) - 0x303a0 (.) = 0xf0fffeff
+// bar@GOTPCREL+4 = 0x20390 (got entry for `bar`) - 0x303a4 (.) + 4 = 0xf0fffeff
+// bar@GOTPCREL-4 = 0x20390 (got entry for `bar`) - 0x303a8 (.) - 4 = 0xe4fffeff
+// CHECK:      Contents of section .data:
+// CHECK-NEXT:  {{.*}} f0fffeff f0fffeff e4fffeff
+  .word bar@GOTPCREL
+  .word bar@GOTPCREL+4
+  .word bar@GOTPCREL-4
+
+// WARN: relocation R_AARCH64_GOTPCREL32 out of range: {{.*}} is not in [-2147483648, 2147483647]; references 'baz'
+// WARN: relocation R_AARCH64_GOTPCREL32 out of range: {{.*}} is not in [-2147483648, 2147483647]; references 'baz'
+  .word baz@GOTPCREL+0xffffffff
+  .word baz@GOTPCREL-0xffffffff

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

@@ -59,6 +59,7 @@ ELF_RELOC(R_AARCH64_ADR_GOT_PAGE,                    0x137)
 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_TLSGD_ADR_PREL21,                0x200)
 ELF_RELOC(R_AARCH64_TLSGD_ADR_PAGE21,                0x201)
 ELF_RELOC(R_AARCH64_TLSGD_ADD_LO12_NC,               0x202)

llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFObjectWriter.cpp

@@ -120,7 +120,8 @@ unsigned AArch64ELFObjectWriter::getRelocType(MCContext &Ctx,
 
   assert((!Target.getSymA() ||
           Target.getSymA()->getKind() == MCSymbolRefExpr::VK_None ||
-          Target.getSymA()->getKind() == MCSymbolRefExpr::VK_PLT) &&
+          Target.getSymA()->getKind() == MCSymbolRefExpr::VK_PLT ||
+          Target.getSymA()->getKind() == MCSymbolRefExpr::VK_GOTPCREL) &&
          "Should only be expression-level modifiers here");
 
   assert((!Target.getSymB() ||
@@ -206,7 +207,10 @@ unsigned AArch64ELFObjectWriter::getRelocType(MCContext &Ctx,
     case FK_Data_2:
       return R_CLS(ABS16);
     case FK_Data_4:
-      return R_CLS(ABS32);
+      return (!IsILP32 &&
+              Target.getAccessVariant() == MCSymbolRefExpr::VK_GOTPCREL)
+                 ? ELF::R_AARCH64_GOTPCREL32
+                 : R_CLS(ABS32);
     case FK_Data_8:
       if (IsILP32) {
         Ctx.reportError(Fixup.getLoc(),

llvm/test/MC/AArch64/elf-reloc-gotpcrel32.s

@@ -0,0 +1,14 @@
+// RUN: llvm-mc -triple=aarch64 -filetype=obj %s -o - | \
+// RUN:   llvm-readobj -r - | FileCheck %s
+
+        .section .data
+this:
+        .word this@GOTPCREL
+        .word extern_sym@GOTPCREL+4
+        .word negative_offset@GOTPCREL-4
+
+// CHECK:      Section ({{.*}}) .rela.data
+// CHECK-NEXT:   0x0 R_AARCH64_GOTPCREL32 this 0x0
+// CHECK-NEXT:   0x4 R_AARCH64_GOTPCREL32 extern_sym 0x4
+// CHECK-NEXT:   0x8 R_AARCH64_GOTPCREL32 negative_offset 0xFFFFFFFFFFFFFFFC
+// CHECK-NEXT: }