ffa829c4c5
For a label difference `A-B` in assembly, if A and B are separated by a linker-relaxable instruction, we should emit a pair of ADD/SUB relocations (e.g. R_RISCV_ADD32/R_RISCV_SUB32, R_RISCV_ADD64/R_RISCV_SUB64). However, the decision is made upfront at parsing time with inadequate heuristics (`requiresFixup`). As a result, LLVM integrated assembler incorrectly suppresses R_RISCV_ADD32/R_RISCV_SUB32 for the following code: ``` // Simplified from a workaround https://android-review.googlesource.com/c/platform/art/+/2619609 // Both end and begin are not defined yet. We decide ADD/SUB relocations upfront and don't know they will be needed. .4byte end-begin begin: call foo end: ``` To fix the bug, make two primary changes: * Delete `requiresFixups` and the overridden emitValueImpl (from D103539). This deletion requires accurate evaluateAsAbolute (D153097). * In MCAssembler::evaluateFixup, call handleAddSubRelocations to emit ADD/SUB relocations. However, there is a remaining issue in MCExpr.cpp:AttemptToFoldSymbolOffsetDifference. With MCAsmLayout, we may incorrectly fold A-B even when A and B are separated by a linker-relaxable instruction. This deficiency is acknowledged (see D153097), but was previously bypassed by eagerly emitting ADD/SUB using `requiresFixups`. To address this, we partially reintroduce `canFold` (from D61584, removed by D103539). Some expressions (e.g. .size and .fill) need to take the `MCAsmLayout` code path in AttemptToFoldSymbolOffsetDifference, avoiding relocations (weird, but matching GNU assembler and needed to match user expectation). Switch to evaluateKnownAbsolute to leverage the `InSet` condition. As a bonus, this change allows for the removal of some relocations for the FDE `address_range` field in the .eh_frame section. riscv64-64b-pcrel.s contains the main test. Add a linker relaxable instruction to dwarf-riscv-relocs.ll to test what it intends to test. Merge fixups-relax-diff.ll into fixups-diff.ll. Reviewed By: kito-cheng Differential Revision: https://reviews.llvm.org/D155357
49 lines
1.7 KiB
LLVM
49 lines
1.7 KiB
LLVM
; RUN: llc -filetype=obj -mtriple=riscv32 -mattr=+relax %s -o - \
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; RUN: | llvm-readobj -r - | FileCheck %s
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; RUN: llc -filetype=obj -mtriple=riscv32 -mattr=-relax %s -o - \
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; RUN: | llvm-readobj -r - | FileCheck %s
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;; b-a in the inline asm is unaffected by linker relaxation, so we don't emit
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;; relocations.
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;; b-a in the inline asm and DW_AT_high_pc are unaffected by linker relaxation,
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;; so we don't emit ADD/SUB relocations.
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;; See also MC/RISCV/fixups-expr.s.
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source_filename = "tmp.c"
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target datalayout = "e-m:e-p:32:32-i64:64-n32-S128"
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target triple = "riscv32"
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define i32 @main() !dbg !7 {
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entry:
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%retval = alloca i32, align 4
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store i32 0, ptr %retval, align 4
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call void asm sideeffect "a:\0Ab:\0A.dword b-a", ""()
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ret i32 0
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}
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; CHECK: Section {{.*}} .rela.debug_info {
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; CHECK-NOT: R_RISCV_ADD32
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; CHECK: }
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; CHECK: Section {{.*}} .rela.eh_frame {
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; CHECK-NEXT: 0x1C R_RISCV_32_PCREL <null> 0x0
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; CHECK-NEXT: }
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!3, !4, !5}
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!llvm.ident = !{!6}
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!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
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!1 = !DIFile(filename: "fixups-diff.ll", directory: "test/MC/RISCV")
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!2 = !{}
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!3 = !{i32 2, !"Dwarf Version", i32 4}
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!4 = !{i32 2, !"Debug Info Version", i32 3}
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!5 = !{i32 1, !"wchar_size", i32 4}
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!6 = !{!"clang"}
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!7 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 1, type: !8, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: false, unit: !0)
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!8 = !DISubroutineType(types: !9)
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!9 = !{!10}
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!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
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!11 = !DILocation(line: 2, column: 3, scope: !7)
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