[all-commits] [llvm/llvm-project] e0a656: [XRay] Make xray_fn_idx entries PC-relative

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: e0a6561ec9ec10f8c0c43b15dfcbbc3c57d37d3f
      https://github.com/llvm/llvm-project/commit/e0a6561ec9ec10f8c0c43b15dfcbbc3c57d37d3f
  Author: Fangrui Song <i at maskray.me>
  Date:   2023-06-20 (Tue, 20 Jun 2023)

  Changed paths:
    M clang/test/CodeGen/xray-function-index.c
    M compiler-rt/lib/xray/xray_interface.cpp
    M compiler-rt/lib/xray/xray_interface_internal.h
    M llvm/include/llvm/MC/MCContext.h
    M llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
    M llvm/lib/MC/MCContext.cpp
    M llvm/test/CodeGen/AArch64/xray-tail-call-sled.ll
    M llvm/test/CodeGen/ARM/xray-armv6-attribute-instrumentation.ll
    M llvm/test/CodeGen/ARM/xray-armv7-attribute-instrumentation.ll
    M llvm/test/CodeGen/Hexagon/xray.ll
    M llvm/test/CodeGen/PowerPC/xray-attribute-instrumentation.ll
    M llvm/test/CodeGen/X86/xray-attribute-instrumentation.ll
    M llvm/test/CodeGen/X86/xray-partial-instrumentation-skip-entry.ll
    M llvm/test/CodeGen/X86/xray-partial-instrumentation-skip-exit.ll
    M llvm/test/CodeGen/X86/xray-tail-call-sled.ll
    M llvm/test/DebugInfo/X86/xray-split-dwarf-interaction.ll

  Log Message:
  -----------
  [XRay] Make xray_fn_idx entries PC-relative

As mentioned by commit c5d38924dc6688c15b3fa133abeb3626e8f0767c (Apr 2020),
PC-relative entries avoid dynamic relocations and can therefore make the
section read-only.

This is similar to D78082 and D78590. We cannot commit to support
compiler/runtime built at different versions, so just don't play with versions.

For Mach-O support (incomplete yet), we use non-temporary `lxray_fn_idx[0-9]+`
symbols. Label differences are represented as a pair of UNSIGNED and SUBTRACTOR
relocations. The SUBTRACTOR external relocation requires r_extern==1 (needs to
reference a symbol table entry) which can be satisfied by `lxray_fn_idx[0-9]+`.
A `lxray_fn_idx[0-9]+` symbol also serves as the atom for this dead-strippable
section (follow-up to commit b9a134aa629de23a1dcf4be32e946e4e308fc64d).

Differential Revision: https://reviews.llvm.org/D152661