[llvm][lld] Support R_RISCV_GOT32_PCREL

This is the followup implementation to
riscv-non-isa/riscv-elf-psabi-doc#402 that
supports this relocation in llvm and lld.

Author: PiJoules

lld/ELF/Arch/RISCV.cpp

@@ -290,6 +290,7 @@ RelExpr RISCV::getRelExpr(const RelType type, const Symbol &s,
   case R_RISCV_PLT32:
     return R_PLT_PC;
   case R_RISCV_GOT_HI20:
+  case R_RISCV_GOT32_PCREL:
     return R_GOT_PC;
   case R_RISCV_PCREL_LO12_I:
   case R_RISCV_PCREL_LO12_S:
@@ -499,6 +500,8 @@ void RISCV::relocate(uint8_t *loc, const Relocation &rel, uint64_t val) const {
   case R_RISCV_SET32:
   case R_RISCV_32_PCREL:
   case R_RISCV_PLT32:
+  case R_RISCV_GOT32_PCREL:
+    checkInt(loc, val, 32, rel);
     write32le(loc, val);
     return;
 

lld/test/ELF/riscv64-reloc-got32-pcrel.s

@@ -0,0 +1,27 @@
+// REQUIRES: riscv
+// RUN: llvm-mc -filetype=obj -triple=riscv64 %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 0000000000002390
+
+  .section .data
+  .globl bar
+bar:
+
+  .globl _start
+_start:  // PC = 0x33a8
+// bar@GOTPCREL   = 0x2398 (got entry for `bar`) - 0x33a8 (.) = 0xf0efffff
+// bar@GOTPCREL+4 = 0x2398 (got entry for `bar`) - 0x33ac (.) + 4 = 0xf0efffff
+// bar@GOTPCREL-4 = 0x2398 (got entry for `bar`) - 0x33b0 (.) - 4 = 0xe4efffff
+// CHECK:      Contents of section .data:
+// CHECK-NEXT:  {{.*}} f0efffff f0efffff e4efffff
+  .word bar@GOTPCREL
+  .word bar@GOTPCREL+4
+  .word bar@GOTPCREL-4
+
+// WARN: relocation R_RISCV_GOT32_PCREL out of range: {{.*}} is not in [-2147483648, 2147483647]; references 'baz'
+// WARN: relocation R_RISCV_GOT32_PCREL out of range: {{.*}} is not in [-2147483648, 2147483647]; references 'baz'
+  .word baz@GOTPCREL+0xffffffff
+  .word baz@GOTPCREL-0xffffffff

llvm/include/llvm/BinaryFormat/ELFRelocs/RISCV.def

@@ -40,8 +40,7 @@ ELF_RELOC(R_RISCV_SUB8,              37)
 ELF_RELOC(R_RISCV_SUB16,             38)
 ELF_RELOC(R_RISCV_SUB32,             39)
 ELF_RELOC(R_RISCV_SUB64,             40)
-ELF_RELOC(R_RISCV_GNU_VTINHERIT,     41)
-ELF_RELOC(R_RISCV_GNU_VTENTRY,       42)
+ELF_RELOC(R_RISCV_GOT32_PCREL,       41)
 ELF_RELOC(R_RISCV_ALIGN,             43)
 ELF_RELOC(R_RISCV_RVC_BRANCH,        44)
 ELF_RELOC(R_RISCV_RVC_JUMP,          45)

llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFObjectWriter.cpp

@@ -106,6 +106,8 @@ unsigned RISCVELFObjectWriter::getRelocType(MCContext &Ctx,
     if (Expr->getKind() == MCExpr::Target &&
         cast<RISCVMCExpr>(Expr)->getKind() == RISCVMCExpr::VK_RISCV_32_PCREL)
       return ELF::R_RISCV_32_PCREL;
+    if (Target.getSymA()->getKind() == MCSymbolRefExpr::VK_GOTPCREL)
+      return ELF::R_RISCV_GOT32_PCREL;
     return ELF::R_RISCV_32;
   case FK_Data_8:
     return ELF::R_RISCV_64;

llvm/test/MC/RISCV/elf-reloc-got32-pcrel.s

@@ -0,0 +1,14 @@
+// RUN: llvm-mc -triple=riscv64 -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_RISCV_GOT32_PCREL this 0x0
+// CHECK-NEXT:   0x4 R_RISCV_GOT32_PCREL extern_sym 0x4
+// CHECK-NEXT:   0x8 R_RISCV_GOT32_PCREL negative_offset 0xFFFFFFFFFFFFFFFC
+// CHECK-NEXT: }