[LoongArch] Produce a R_LARCH_32_PCREL relocation

[wangleiat]

Summary

LoongArchELFObjectWriter::getRelocType check IsPCRel for FK_Data_4
(which we produce a R_LARCH_32_PCREL relocation for if IsPCRel).

R_LARCH_32_PCREL is required for FDE relocation.

[xen0n]

Nice catch...

llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchELFObjectWriter.cpp

default:
     return ELF::R_LARCH_NONE;
   case FK_Data_1:
     Ctx.reportError(Fixup.getLoc(), "1-byte data relocations not supported");
     return ELF::R_LARCH_NONE;
   case FK_Data_2:
     Ctx.reportError(Fixup.getLoc(), "2-byte data relocations not supported");
     return ELF::R_LARCH_NONE;
   case FK_Data_4:
-    return ELF::R_LARCH_32;
+    return IsPCRel ? ELF::R_LARCH_32_PCREL : ELF::R_LARCH_32;
   case FK_Data_8:
     return ELF::R_LARCH_64;
   case LoongArch::fixup_loongarch_b16:
     return ELF::R_LARCH_B16;
   case LoongArch::fixup_loongarch_b21:
     return ELF::R_LARCH_B21;
   case LoongArch::fixup_loongarch_b26:
     return ELF::R_LARCH_B26;

llvm/test/MC/LoongArch/Relocations/fde-reloc.s

+# RUN: llvm-mc --filetype=obj --triple=loongarch64 < %s \
+# RUN:     | llvm-readobj -r - | FileCheck %s
+
+## Ensure that the eh_frame records the symbolic difference with
+## the R_LARCH_32_PCREL relocation.
+
+func:
+ .cfi_startproc
+  ret
+ .cfi_endproc
+
+# CHECK:   Section (4) .rela.eh_frame {
+# CHECK-NEXT:   0x1C R_LARCH_32_PCREL - 0x0
+# CHECK-NEXT: }