http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59693
Bug ID: 59693
Summary: man page says "extern" declarations are unaffected by
-fvisibility
Product: gcc
Version: 4.8.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: jed at 59A2 dot org
The gcc man page says the following:
extern declarations are not affected by -fvisibility, so a lot of
code can be recompiled with -fvisibility=hidden with no
modifications. However, this means that calls to "extern" functions
with no explicit visibility use the PLT, so it is more effective to
use "__attribute ((visibility))" and/or "#pragma GCC visibility" to
tell the compiler which "extern" declarations should be treated as
hidden.
I read this to mean that functions and data declared "extern" will have default
visibility when compiled with -fvisibility=hidden, but that is not the case:
$ cat externvis.c
EXTERN int foo_func(void);
EXTERN int foo_data;
int foo_func(void) {
return 0;
}
int foo_data;
$ gcc -c externvis.c -DEXTERN=extern -fvisibility=hidden && objdump -t
externvis.o | grep foo
0000000000000000 g F .text 000000000000000b .hidden foo_func
0000000000000004 O *COM* 0000000000000004 .hidden foo_data
$ gcc -c externvis.c -DEXTERN='__attribute((visibility("default")))'
-fvisibility=hidden && objdump -t externvis.o | grep foo
0000000000000004 O *COM* 0000000000000004 foo_data
0000000000000000 g F .text 000000000000000b foo_func
$ gcc -c externvis.c -DEXTERN=extern && objdump -t externvis.o | grep foo
0000000000000000 g F .text 000000000000000b foo_func
0000000000000004 O *COM* 0000000000000004 foo_data
It seems to me that either gcc's behavior should be changed to match the
documentation or this paragraph should be removed/modified. Note that clang's
behavior matches gcc (not the man page).
