[MC] Put the pending fixups into relocation offset symbol's fragment

[StephenFan]

Summary

For .reloc directive, if the relocation offset is a symbol, then the relocation entry should be placed into relocation section and its sh_info should point to the section where relocation offset symbol at.

Test case:

.text
  ret
  nop
  nop
  .reloc foo, R_RISCV_32, 6

.data
.globl foo
foo:
  .word 0
  .word 0
  .word 0

The relocation entry should be placed into .reloc.data. And it is also what gnu as does.

[MaskRay]

llvm/lib/MC/MCObjectStreamer.cpp

131

Several cases are not covered by tests. They need tests.

llvm/test/MC/RISCV/reloc-directive.s

26

[StephenFan]

Add tests for FT_Dwarf and FT_PseudoProbe.

[StephenFan]

llvm/lib/MC/MCObjectStreamer.cpp

129

Hi @MaskRay , The test case of FT_Relaxable is not added. Because I don't know how to define a symbol which its fragment is FT_Relaxable. Do you have some ideas ?

137

I found that FT_CVDefRange is only used by COFF. Does COFF support .reloc directive?

[MaskRay]

LGTM.

llvm/test/MC/RISCV/reloc-directive.s

34

# CHECK:      Section ({{.*}}) .rela.pseudoprobe {
# CHECK-NEXT:   0x0 R_RISCV_32 - 0x6
# CHECK-NEXT: }

llvm/lib/MC/MCObjectStreamer.cpp

void MCObjectStreamer::resolvePendingFixups() {
   for (PendingMCFixup &PendingFixup : PendingFixups) {
     if (!PendingFixup.Sym || PendingFixup.Sym->isUndefined ()) {
       getContext().reportError(PendingFixup.Fixup.getLoc(),
                                "unresolved relocation offset");
       continue;
     }
     flushPendingLabels(PendingFixup.DF, PendingFixup.DF->getContents().size());
     PendingFixup.Fixup.setOffset(PendingFixup.Sym->getOffset());
+
+    // If the location symbol to relocate is in MCEncodedFragmentWithFixups,
+    // put the Fixup into location symbol's fragment. Otherwise
+    // put into PendingFixup.DF
+    MCFragment *SymFragment = PendingFixup.Sym->getFragment();
+    switch (SymFragment->getKind()) {
+    case MCFragment::FT_Relaxable:
+    case MCFragment::FT_Dwarf:
+    case MCFragment::FT_PseudoProbe:
+      cast<MCEncodedFragmentWithFixups<8, 1>>(SymFragment)
+          ->getFixups()
+          .push_back(PendingFixup.Fixup);
+      break;
+    case MCFragment::FT_Data:
+    case MCFragment::FT_CVDefRange:
+      cast<MCEncodedFragmentWithFixups<32, 4>>(SymFragment)
+          ->getFixups()
+          .push_back(PendingFixup.Fixup);
+      break;
+    default:
       PendingFixup.DF->getFixups().push_back(PendingFixup.Fixup);
+      break;
+    }
   }
   PendingFixups.clear();
 }
 
 // As a compile-time optimization, avoid allocating and evaluating an MCExpr
 // tree for (Hi - Lo) when Hi and Lo are offsets into the same fragment.
 static Optional<uint64_t> absoluteSymbolDiff(const MCSymbol *Hi,
                                              const MCSymbol *Lo) {

llvm/test/MC/RISCV/reloc-directive.s

 # CHECK-NEXT: 0x4 R_RISCV_NONE foo 0x4
 # CHECK-NEXT: 0x0 R_RISCV_NONE - 0x8
 # CHECK-NEXT: 0x0 R_RISCV_32 .data 0x2
 # CHECK-NEXT: 0x0 R_RISCV_SET32 foo 0x3
 # CHECK-NEXT: 0x0 R_RISCV_32_PCREL - 0x5
 # CHECK-NEXT: 0x0 R_RISCV_NONE - 0x9
 # CHECK-NEXT: 0x0 R_RISCV_32 - 0x9
 # CHECK-NEXT: 0x0 R_RISCV_64 - 0x9
+
+# CHECK: Section ({{.*}}) .rela.data
+# CHECK-NEXT: 0x0 R_RISCV_32 - 0x6
+# CHECK-NEXT: }
 .text
   ret
   nop
   nop
   .reloc 8, R_RISCV_NONE, .data
   .reloc 4, R_RISCV_NONE, foo+4
   .reloc 0, R_RISCV_NONE, 8
 
   .reloc 0, R_RISCV_32, .data+2
   .reloc 0, R_RISCV_SET32, foo+3
   .reloc 0, R_RISCV_32_PCREL, 5
 
   .reloc 0, BFD_RELOC_NONE, 9
   .reloc 0, BFD_RELOC_32, 9
   .reloc 0, BFD_RELOC_64, 9
 
+  .reloc foo, R_RISCV_32, 6
+
 .data
 .globl foo
 foo:
   .word 0
   .word 0
   .word 0