choose exported symbols when linking an elf application and shared library

0
votes

when linking an elf application or share library, I want to choose which symbols to export. By default, when linking an application no function symbol is exported and when linking a shared library all function symbols are exported. Is there any way to control which symbols to export? When linking an application, I can use -rdynamic or -Wl,--export-dynamic to get all symbols, and I can use -Wl,--dynamic-list <symfile> to get only some symbols. However when linking a library, are those options ignored?

2
linkerelf
Possible duplicate of Limiting visibility of symbols when linking shared libraries – Employed Russian

2 Answers

3
votes

Found out after testing a little:

  • for ELF applications, you can use -rdynamic or -Wl,--export-dynamic to export all symbols, or you can use -Wl,--dynamic-list <sym-file> to export only some symbols when linking your application through gcc.

  • for ELF libraries, you can't use -rdynamic, -Wl,--export-dynamic or -Wl,--dynamic-list <symfile>, you must use -Wl,--version-script=<verfile> when linking your library through gcc.

The version-script and the sym-file are almost the same, except that for sym-file you do not code a version and a scope. Documentation: gnu ld

2
votes

Is there any way to control which symbols to export?

The usual way to control symbol visibility in shared library is either

  1. Use linker script, as described here, or
  2. Use __attribute__((visibility("default"))) on symbols you explicitly want to export and build with -fvisibility=hidden (which will hide everything else).