On Tue, Feb 3, 2015 at 5:16 PM, H.J. Lu <[email protected]> wrote:
> On Tue, Feb 3, 2015 at 2:19 PM, Jakub Jelinek <[email protected]> wrote:
>> On Tue, Feb 03, 2015 at 02:03:14PM -0800, H.J. Lu wrote:
>>> So we aren't SYMBOL_REF_EXTERNAL_P nor
>>> SYMBOL_REF_LOCAL_P. What do we reference?
>>
>> That is reasonable. There is no guarantee the extern weak symbol is local,
>> it could very well be non-local. All that you know about the symbols is
>> that its address is non-NULL in that case.
>>
>
> This may be true for shared library. But it isn't true for PIE:
Also, gcc and g++ are inconsistent about something even more simple:
$ cat x.c
int a;
int main() {
printf("%d\n", a);
}
With gcc -fPIE x.c
SYMBOL_REF_LOCAL_P(op0) = false
With g++ -fPIE x.c
SYMBOL_REF_LOCAL_P(op0) = true
Sri
>
> [hjl@gnu-6 copyreloc-3]$ cat x.c
> __attribute__((weak))
> int a;
>
> extern void bar (void);
>
> int main()
> {
> if (a != 0)
> __builtin_abort();
> bar ();
> if (a != 30)
> __builtin_abort();
> return 0;
> }
> [hjl@gnu-6 copyreloc-3]$ cat bar.c
> int a = -1;
>
> void
> bar ()
> {
> a = 30;
> }
> [hjl@gnu-6 copyreloc-3]$ make
> gcc -pie -O3 -g -fuse-ld=gold -fpie -c x.i
> gcc -pie -O3 -g -fuse-ld=gold -fpic -c -o bar.o bar.c
> gcc -pie -shared -o libbar.so bar.o
> gcc -pie -O3 -g -fuse-ld=gold -o x x.o libbar.so -Wl,-R,.
> ./x
> [hjl@gnu-6 copyreloc-3]$
>
> Even if a common symbol, a, is weak, all references to
> a within PIE is local.
>
> --
> H.J.
