[all-commits] [llvm/llvm-project] 697084: [compiler-rt/profile] Hide __llvm_profile_raw_version

[pirama-arumuga-nainar via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 69708477be258dbea2711f6a35c02685659b49d3
      https://github.com/llvm/llvm-project/commit/69708477be258dbea2711f6a35c02685659b49d3
  Author: Pirama Arumuga Nainar <pirama at google.com>
  Date:   2021-10-15 (Fri, 15 Oct 2021)

  Changed paths:
    M compiler-rt/lib/profile/InstrProfiling.h
    M compiler-rt/lib/profile/InstrProfilingVersionVar.c

  Log Message:
  -----------
  [compiler-rt/profile] Hide __llvm_profile_raw_version

Hide __llvm_profile_raw_version so as not to resolve reference from a
dependent shared object.  Since libclang_rt.profile is added later in
the command line, a definition of __llvm_profile_raw_version is not
included if it is provided from an earlier object, e.g.  from a shared
dependency.

This causes an extra dependence edge where if libA.so depends on libB.so
and both are coverage-instrumented, libA.so uses libB.so's definition of
__llvm_profile_raw_version.  This leads to a runtime link failure if the
libB.so available at runtime does not provide this symbol (but provides
the other dependent symbols).  Such a scenario can occur in Android's
mainline modules.
E.g.:
  ld -o libB.so libclang_rt.profile-x86_64.a
  ld -o libA.so -l B libclang_rt.profile-x86_64.a

libB.so has a global definition of __llvm_profile_raw_version.  libA.so
uses libB.so's definition of __llvm_profile_raw_version.  At runtime,
libB.so may not be coverage-instrumented (i.e. not export
__llvm_profile_raw_version) so runtime linking of libA.so will fail.

Marking this symbol as hidden forces each binary to use the definition
of __llvm_profile_raw_version from libclang_rt.profile.

Differential Revision: https://reviews.llvm.org/D111759