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[RISCV] Force relocations if initial MCSubtargetInfo contains FeatureRelax #77436

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Jan 9, 2024
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[RISCV] Force relocations if initial MCSubtargetInfo contains FeatureRelax #77436

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[RISCV] Force relocations if initial MCSubtargetInfo contains Feature…
MaskRay Jan 9, 2024
c9726b0
test: link to https://github.com/ClangBuiltLinux/linux/issues/1965
MaskRay Jan 9, 2024
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7 changes: 7 additions & 0 deletions llvm/lib/Target/RISCV/MCTargetDesc/RISCVELFStreamer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,13 @@ RISCVTargetELFStreamer::RISCVTargetELFStreamer(MCStreamer &S,
auto &MAB = static_cast<RISCVAsmBackend &>(MCA.getBackend());
setTargetABI(RISCVABI::computeTargetABI(STI.getTargetTriple(), Features,
MAB.getTargetOptions().getABIName()));
// `j label` in `.option norelax; j label; .option relax; ...; label:` needs a
// relocation to ensure the jump target is correct after linking. This is due
// to a limitation that shouldForceRelocation has to make the decision upfront
// without knowing a possibly future .option relax. When RISCVAsmParser is used,
// its ParseInstruction may call setForceRelocs as well.
if (STI.hasFeature(RISCV::FeatureRelax))
static_cast<RISCVAsmBackend &>(MAB).setForceRelocs();
}

RISCVELFStreamer &RISCVTargetELFStreamer::getStreamer() {
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31 changes: 31 additions & 0 deletions llvm/test/CodeGen/RISCV/option-relax-relocation.ll
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@@ -0,0 +1,31 @@
;; With +relax, J below needs a relocation to ensure the target is correct
;; after linker relaxation. See https://github.com/ClangBuiltLinux/linux/issues/1965

; RUN: llc -mtriple=riscv64 -mattr=-relax -filetype=obj < %s \
; RUN: | llvm-objdump -d -r - | FileCheck %s
; RUN: llc -mtriple=riscv64 -mattr=+relax -filetype=obj < %s \
; RUN: | llvm-objdump -d -r - | FileCheck %s --check-prefixes=CHECK,RELAX

; CHECK: j {{.*}}
; RELAX-NEXT: R_RISCV_JAL {{.*}}
; CHECK-NEXT: auipc ra, 0x0
; CHECK-NEXT: R_RISCV_CALL_PLT f
; RELAX-NEXT: R_RISCV_RELAX *ABS*
; CHECK-NEXT: jalr ra

define dso_local noundef signext i32 @main() local_unnamed_addr #0 {
entry:
callbr void asm sideeffect ".option push\0A.option norvc\0A.option norelax\0Aj $0\0A.option pop\0A", "!i"() #2
to label %asm.fallthrough [label %label]

asm.fallthrough: ; preds = %entry
tail call void @f()
br label %label

label: ; preds = %asm.fallthrough, %entry
ret i32 0
}

declare void @f()

attributes #0 = { nounwind "target-features"="-c,+relax" }