[Object][RISCV] Resolve R_RISCV_32_PCREL

[luismarques]

Summary

Add support for resolving R_RISCV_32_PCREL relocations. Those aren't actually resolved AFAIK, but support is still needed to avoid llvm-dwarfdump errors. The use of these relocations was introduced in D66419 but the corresponding resolving wasn't added then*. The test adds a check that should catch future unresolved relocations.

*I would blame the reviewer, but it turns out that person was me, so he's exculpated.

[asb]

LGTM, thanks Luis.

[luismarques]

Rebase patch; Tweak enumeration order. Change title [DWARF] to [Object].

llvm/lib/Object/RelocationResolver.cpp

if (R.getType() == ELF::R_HEX_32)
     return S + getELFAddend(R);
   llvm_unreachable("Invalid relocation type");
 }
 
 static bool supportsRISCV(uint64_t Type) {
   switch (Type) {
   case ELF::R_RISCV_NONE:
   case ELF::R_RISCV_32:
+  case ELF::R_RISCV_32_PCREL:
   case ELF::R_RISCV_64:
   case ELF::R_RISCV_SET6:
   case ELF::R_RISCV_SUB6:
   case ELF::R_RISCV_ADD8:
   case ELF::R_RISCV_SUB8:
   case ELF::R_RISCV_ADD16:
   case ELF::R_RISCV_SUB16:
   case ELF::R_RISCV_ADD32:
   case ELF::R_RISCV_SUB32:
   case ELF::R_RISCV_ADD64:
   case ELF::R_RISCV_SUB64:
     return true;
   default:
     return false;
   }
 }
 
 static uint64_t resolveRISCV(RelocationRef R, uint64_t S, uint64_t A) {
   int64_t RA = getELFAddend(R);
   switch (R.getType()) {
   case ELF::R_RISCV_NONE:
     return A;
   case ELF::R_RISCV_32:
     return (S + RA) & 0xFFFFFFFF;
+  case ELF::R_RISCV_32_PCREL:
+    return (S + RA - R.getOffset()) & 0xFFFFFFFF;
   case ELF::R_RISCV_64:
     return S + RA;
   case ELF::R_RISCV_SET6:
     return (A & 0xC0) | ((S + RA) & 0x3F);
   case ELF::R_RISCV_SUB6:
     return (A & 0xC0) | (((A & 0x3F) - (S + RA)) & 0x3F);
   case ELF::R_RISCV_ADD8:
     return (A + (S + RA)) & 0xFF;

llvm/test/DebugInfo/RISCV/relax-debug-frame.ll

 ; RUN: llc -filetype=obj -mtriple=riscv32 -mattr=+relax %s -o - \
 ; RUN:     | llvm-readobj -r | FileCheck -check-prefix=RELAX %s
 ; RUN: llc -filetype=obj -mtriple=riscv32 -mattr=+relax %s -o - \
-; RUN:     | llvm-dwarfdump --debug-frame - \
+; RUN:     | llvm-dwarfdump --debug-frame - 2>&1 \
 ; RUN:     | FileCheck -check-prefix=RELAX-DWARFDUMP %s
 ;
 ; RELAX: Section{{.*}}.rela.{{eh|debug}}_frame {
 ; RELAX-NOT: {{[}]}}
 ; RELAX-NOT: 0x0 R_RISCV_ADD32
 ; RELAX-NOT: 0x0 R_RISCV_SUB32
 ; RELAX-NOT: {{[}]}}
 ; RELAX: 0x20 R_RISCV_ADD32
 ; RELAX: 0x20 R_RISCV_SUB32
 ; RELAX-NOT: {{[}]}}
 ; RELAX: 0x39 R_RISCV_SET6
 ; RELAX: 0x39 R_RISCV_SUB6
 ;
+; RELAX-DWARFDUMP-NOT: error: failed to compute relocation
 ; RELAX-DWARFDUMP: CIE
 ; RELAX-DWARFDUMP: DW_CFA_advance_loc
 ; RELAX-DWARFDUMP: DW_CFA_def_cfa_offset
 ; RELAX-DWARFDUMP: DW_CFA_offset
 source_filename = "frame.c"
 
 ; Function Attrs: noinline nounwind optnone
 define i32 @init() {