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
69 lines
2.1 KiB
LLVM
69 lines
2.1 KiB
LLVM
; RUN: llc -filetype=obj -mtriple=riscv32 -mattr=+relax %s -o %t.o
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; RUN: llvm-readobj -r %t.o | FileCheck -check-prefix=RELAX %s
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; RUN: llvm-dwarfdump --debug-frame %t.o 2>&1 \
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; RUN: | FileCheck -check-prefix=RELAX-DWARFDUMP %s
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;
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; RELAX: Section ({{.*}}) .rela.eh_frame {
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; RELAX-NEXT: 0x1C R_RISCV_32_PCREL <null> 0x0
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; RELAX-NEXT: 0x30 R_RISCV_32_PCREL <null> 0x0
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; RELAX-NEXT: 0x44 R_RISCV_32_PCREL <null> 0x0
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; RELAX-NEXT: 0x48 R_RISCV_ADD32 <null> 0x0
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; RELAX-NEXT: 0x48 R_RISCV_SUB32 <null> 0x0
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; RELAX-NEXT: }
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; RELAX-DWARFDUMP-NOT: error: failed to compute relocation
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; RELAX-DWARFDUMP: FDE
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; RELAX-DWARFDUMP-NEXT: Format:
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; RELAX-DWARFDUMP: DW_CFA_advance_loc: 4
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; RELAX-DWARFDUMP-NEXT: DW_CFA_def_cfa_offset: +16
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; RELAX-DWARFDUMP-EMPTY:
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; RELAX-DWARFDUMP: FDE
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; RELAX-DWARFDUMP: Format:
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; RELAX-DWARFDUMP-NEXT: DW_CFA_advance_loc: 4
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; RELAX-DWARFDUMP-NEXT: DW_CFA_def_cfa_offset: +16
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; RELAX-DWARFDUMP-NEXT: DW_CFA_advance_loc: 4
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; RELAX-DWARFDUMP-NEXT: DW_CFA_offset: X1 -4
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; RELAX-DWARFDUMP-NEXT: DW_CFA_nop
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; RELAX-DWARFDUMP-EMPTY:
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source_filename = "frame.c"
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; Function Attrs: noinline nounwind optnone
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define i32 @init() {
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entry:
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ret i32 0
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}
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; Function Attrs: noinline nounwind optnone
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define i32 @foo(i32 signext %value) {
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entry:
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%value.addr = alloca i32, align 4
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store i32 %value, ptr %value.addr, align 4
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%0 = load i32, ptr %value.addr, align 4
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ret i32 %0
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}
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; Function Attrs: noinline nounwind optnone
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define i32 @bar() {
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entry:
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%result = alloca i32, align 4
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%v = alloca i32, align 4
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%call = call i32 @init()
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store i32 %call, ptr %v, align 4
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%0 = load i32, ptr %v, align 4
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%call1 = call i32 @foo(i32 signext %0)
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store i32 %call1, ptr %result, align 4
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%1 = load i32, ptr %result, align 4
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ret i32 %1
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}
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!3, !4, !5}
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!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
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!1 = !DIFile(filename: "line.c", directory: "./")
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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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