bef8294650
The `__DATA,xray_instr_map` section has label differences like
`.quad Lxray_sled_0-Ltmp0` that is represented as a pair of UNSIGNED and SUBTRACTOR relocations.
LLVM integrated assembler attempts to rewrite A-B into A-B'+offset where B' can
be included in the symbol table. B' is called an atom and should be a
non-temporary symbol in the same section. However, since `xray_instr_map` does
not define a non-temporary symbol, the SUBTRACTOR relocation will have no
associated symbol, and its `r_extern` value will be 0. Therefore, we will see
linker errors like:
error: SUBTRACTOR relocation must be extern at offset 0 of __DATA,xray_instr_map in a.o
To fix this issue, we need to define a non-temporary symbol in the section. We
can accomplish this by renaming `Lxray_sleds_start0` to `lxray_sleds_start0`
("L" to "l").
`lxray_sleds_start0` serves as the atom for this dead-strippable subsection.
With the `S_ATTR_LIVE_SUPPORT` attribute, `ld -dead_strip` will retain
subsections that reference live functions.
Special thanks to Oleksii Lozovskyi for reporting the issue and providing
initial analysis.
Differential Revision: https://reviews.llvm.org/D153239
29 lines
958 B
LLVM
29 lines
958 B
LLVM
; RUN: llc -mtriple=aarch64-unknown-linux-gnu < %s | FileCheck %s --check-prefixes=CHECK,CHECK-LINUX
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; RUN: llc -mtriple=aarch64-apple-darwin < %s | FileCheck %s --check-prefixes=CHECK,CHECK-MACOS
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define i32 @foo() nounwind noinline uwtable "function-instrument"="xray-always" "xray-skip-exit" {
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; CHECK-LABEL: Lxray_sled_0:
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; CHECK-NEXT: b #32
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; CHECK-NEXT: nop
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; CHECK-NEXT: nop
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; CHECK-NEXT: nop
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; CHECK-NEXT: nop
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; CHECK-NEXT: nop
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; CHECK-NEXT: nop
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; CHECK-NEXT: nop
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; CHECK-LABEL: Ltmp0:
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ret i32 0
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; CHECK-NOT: Lxray_sled_1:
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; CHECK: ret
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}
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; CHECK-LINUX-LABEL: .section xray_instr_map,"ao",@progbits,foo{{$}}
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; CHECK-LINUX-LABEL: Lxray_sleds_start0:
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; CHECK-LINUX: .xword .Lxray_sled_0
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; CHECK-LINUX-LABEL: Lxray_sleds_end0:
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; CHECK-MACOS-LABEL: .section __DATA,xray_instr_map,regular,live_support{{$}}
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; CHECK-MACOS-LABEL: lxray_sleds_start0:
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; CHECK-MACOS: .quad Lxray_sled_0
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; CHECK-MACOS-LABEL: Lxray_sleds_end0:
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