I've been on a crusade lately to eliminate warnings from our code and have become more familiar with GCC warning flags (such as -Wall
, -Wno-<warning to disable>
, -fdiagnostics-show-option
, etc.). However I haven't been able to figure out how to disable (or even control) linker warnings. The most common linker warning that I was getting is of the following form:
ld: warning: <some symbol> has different visibility (default) in
<path/to/library.a> and (hidden) in <path/to/my/class.o>
The reason I was getting this was because the library I was using was built using the default
visibility while my application is built with hidden
visibility. I've fixed this by rebuilding the library with hidden
visibility.
My question though is: how would I suppress that warning if I wanted to? It's not something that I need to do now that I've figured out how to fix it but I'm still curious as to how you'd suppress that particular warning — or any linker warnings in general?
Using the -fdiagnostics-show-option
for any of the C/C++/linker flags doesn't say where that warning comes from like with other compiler warnings.
Actually, you can't disable a GCC linker warning, as it's stored in a specific section of the binary library you're linking with. (The section is called .gnu.warning.symbol)
You can however mute it, like this (this is extracted from libc-symbols.h):
Without it:
#include <sys/stat.h>
int main()
{
lchmod("/path/to/whatever", 0666);
return 0;
}
Gives:
$ gcc a.c
/tmp/cc0TGjC8.o: in function « main »:
a.c:(.text+0xf): WARNING: lchmod is not implemented and will always fail
With disabling:
#include <sys/stat.h>
/* We want the .gnu.warning.SYMBOL section to be unallocated. */
#define __make_section_unallocated(section_string) \
__asm__ (".section " section_string "\n\t.previous");
/* When a reference to SYMBOL is encountered, the linker will emit a
warning message MSG. */
#define silent_warning(symbol) \
__make_section_unallocated (".gnu.warning." #symbol)
silent_warning(lchmod)
int main()
{
lchmod("/path/to/whatever", 0666);
return 0;
}
gives:
$ gcc a.c
/tmp/cc195eKj.o: in function « main »:
a.c:(.text+0xf): WARNING:
With hiding:
#include <sys/stat.h>
#define __hide_section_warning(section_string) \
__asm__ (".section " section_string "\n.string \"\rHello world! \"\n\t.previous");
/* If you want to hide the linker's output */
#define hide_warning(symbol) \
__hide_section_warning (".gnu.warning." #symbol)
hide_warning(lchmod)
int main()
{
lchmod("/path/to/whatever", 0666);
return 0;
}
gives:
$ gcc a.c
/tmp/cc195eKj.o: in function « main »:
Hello world!
Obviously, in that case, replace Hello world!
either by multiple space or some advertisement for your wonderful project.