Limiting visibility of symbols when linking shared libraries

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GNU ld can do that on ELF platforms.

Here is how to do it with a linker version script:

/* foo.c */
int foo() { return 42; }
int bar() { return foo() + 1; }
int baz() { return bar() - 1; }

gcc -fPIC -shared -o libfoo.so foo.c && nm -D libfoo.so | grep ' T '

By default, all symbols are exported:

0000000000000718 T _fini
00000000000005b8 T _init
00000000000006b7 T bar
00000000000006c9 T baz
00000000000006ac T foo

Let’s say you want to export only bar() and baz(). Create a “version script” libfoo.version:

FOO {
  global: bar; baz; # explicitly list symbols to be exported
  local: *;         # hide everything else
};

Pass it to the linker:

gcc -fPIC -shared -o libfoo.so foo.c -Wl,--version-script=libfoo.version

Observe exported symbols:

nm -D libfoo.so | grep ' T '
00000000000005f7 T bar
0000000000000609 T baz

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