[ELF] Refine --export-dynamic-symbol semantics to be compatible GNU ld 2.35

Authored by MaskRay on Jun 1 2020, 11:27 AM.


[ELF] Refine --export-dynamic-symbol semantics to be compatible GNU ld 2.35

GNU ld from binutils 2.35 onwards will likely support
--export-dynamic-symbol but with different semantics.


  1. -export-dynamic-symbol is not supported
  2. --export-dynamic-symbol takes a glob argument
  3. --export-dynamic-symbol can suppress binding the references to the definition within the shared object if (-Bsymbolic or -Bsymbolic-functions)
  4. --export-dynamic-symbol does not imply -u

I don't think the first three points can affect any user.
For the fourth point, Not implying -u can lead to some archive members unfetched.
Add -u foo to restore the previous behavior.

Exact semantics:

  • -no-pie or -pie: matched non-local defined symbols will be added to the dynamic symbol table.
  • -shared: matched non-local STV_DEFAULT symbols will not be bound to definitions within the shared object even if they would otherwise be due to -Bsymbolic, -Bsymbolic-functions, or --dynamic-list.

Reviewed By: psmith

Differential Revision: https://reviews.llvm.org/D80487