ELF visibility test

elf_visibility_test.sh

$ cat prog.c
#include <stdio.h>

void func();

void xyz() {
  printf("main-xyz\n");
}

void xyz2() {
  printf("main-xyz2\n");
}

int main(void) {
  func();
  return 0;
}

$ cat foo.c
#include <stdio.h>

void xyz() {
  printf("foo-xyz\n");
}

void xyz2() {
  printf("foo-xyz2\n");
}

void func() {
  xyz();
  xyz2();
}

#
# Default behavior
#

$ gcc -g -c -fPIC -Wall -c foo.c
$ gcc -g -shared -o libfoo.so foo.o
$ nm libfoo.so | grep xyz
0000000000000730 T xyz
0000000000000743 T xyz2
$ gcc -g -o prog prog.c libfoo.so
$ LD_LIBRARY_PATH=. ./prog
main-xyz
main-xyz2

#
# Use -Bsymbolic to reference global symbols internally.
#

$ gcc -g -shared -o libfoo.so foo.o -Wl,-Bsymbolic
$ nm libfoo.so | grep xyz
00000000000006e0 T xyz
00000000000006f3 T xyz2
$ LD_LIBRARY_PATH=. ./prog
foo-xyz
foo-xyz2


#
# Use version script to hide local symbols.
#

$ cat libfoo.map
FOO {
  global: func; xyz2; # explicitly list symbols to be exported.
  local: *;           # hide the rest.
};
$ gcc -g -shared -o libfoo.so foo.o -Wl,--version-script=libfoo.map
$ nm libfoo.so | grep xyz  # T/t means global/local symbol
0000000000000690 t xyz
00000000000006a3 T xyz2
$ LD_LIBRARY_PATH=. ./prog
foo-xyz
main-xyz2