[PATCH] D153239: [XRay] Make xray_instr_map compatible with Mach-O

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
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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.
The SUBTRACTOR external relocation needs to reference a non-temporary symbol while
`__DATA,xray_instr_map` doesn't currently define one, 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, change `Lxray_sleds_start0` to `lxray_sleds_start0` to provide an
non-temporary symbol that is linker private (which will not appear in the linked
image).

`lxray_sleds_start0` also 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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D153239

Files:
  llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
  llvm/test/CodeGen/AArch64/xray-attribute-instrumentation.ll
  llvm/test/CodeGen/AArch64/xray-omit-function-index.ll
  llvm/test/CodeGen/AArch64/xray-partial-instrumentation-skip-entry.ll
  llvm/test/CodeGen/AArch64/xray-partial-instrumentation-skip-exit.ll
  llvm/test/CodeGen/AArch64/xray-tail-call-sled.ll
  llvm/test/CodeGen/ARM/xray-armv6-attribute-instrumentation.ll
  llvm/test/CodeGen/ARM/xray-armv7-attribute-instrumentation.ll
  llvm/test/CodeGen/X86/xray-attribute-instrumentation.ll
  llvm/test/CodeGen/X86/xray-log-args.ll
  llvm/test/CodeGen/X86/xray-partial-instrumentation-skip-entry.ll
  llvm/test/CodeGen/X86/xray-partial-instrumentation-skip-exit.ll
  llvm/test/CodeGen/X86/xray-tail-call-sled.ll

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