[RISCV] Fix evaluation of %pcrel_lo
The following testcase
function:
.Lpcrel_label1:
auipc a0, %pcrel_hi(other_function)
addi a1, a0, %pcrel_lo(.Lpcrel_label1)
.p2align 2 # Causes a new fragment to be emitted
.type other_function,@function
other_function:
ret
exposes an odd behaviour in which only the %pcrel_hi relocation is
evaluated but not the %pcrel_lo.
$ llvm-mc -triple riscv64 -filetype obj t.s | llvm-objdump -d -r -
<stdin>: file format ELF64-riscv
Disassembly of section .text:
0000000000000000 function:
0: 17 05 00 00 auipc a0, 0
4: 93 05 05 00 mv a1, a0
0000000000000004: R_RISCV_PCREL_LO12_I other_function+4
0000000000000008 other_function:
8: 67 80 00 00 ret
The reason seems to be that in RISCVAsmBackend::shouldForceRelocation we
only consider the fragment but in RISCVMCExpr::evaluatePCRelLo we
consider the section. This usually works but there are cases where the
section may still be the same but the fragment may be another one. In
that case we end forcing a %pcrel_lo relocation without any %pcrel_hi.
This patch makes RISCVAsmBackend::shouldForceRelocation use the section,
if any, to determine if the relocation must be forced or not.
Differential Revision: https://reviews.llvm.org/D60657
diff --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp
index f6b727a..5881a0a 100644
--- a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp
+++ b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp
@@ -64,11 +64,15 @@
case RISCV::fixup_riscv_tls_gd_hi20:
ShouldForce = true;
break;
- case RISCV::fixup_riscv_pcrel_hi20:
- ShouldForce = T->getValue()->findAssociatedFragment() !=
- Fixup.getValue()->findAssociatedFragment();
+ case RISCV::fixup_riscv_pcrel_hi20: {
+ MCFragment *TFragment = T->getValue()->findAssociatedFragment();
+ MCFragment *FixupFragment = Fixup.getValue()->findAssociatedFragment();
+ assert(FixupFragment && "We should have a fragment for this fixup");
+ ShouldForce =
+ !TFragment || TFragment->getParent() != FixupFragment->getParent();
break;
}
+ }
break;
}