Hi, Sorry for coming back to this issue after a while. I am still puzzled by this. The following are two test files:
a.c #include <string.h> #include <stdio.h> extern int foo(int); void bar() { printf("bar\n"); } extern int src[], dst[]; int vvvvvv; int main() { int ret; vvvvvv = 12; ret = foo(20); memcpy(dst, src, 100); return ret + 3; } b.c #include <stdio.h> int src[100]; int dst[100]; extern int vvvvvv; extern void bar(); int foo(int c) { printf("Hello world: %d\n", c); bar(); return 1000 + vvvvvv; } I compiled with following steps ~/work/install-x86/bin/gcc -flto a.c -O2 -c ~/work/install-x86/bin/gcc b.c -O2 -c ar cru libb.a b.o ~/work/install-x86/bin/gcc -flto a.o -L. -lb -O2 -fuse-linker-plugin -o f -fwhole-program -save-temps Since you both mentioned that resolution file is not used to replace externally_visible attribute yet, I expect there will be link errors regarding both vvvvvv and bar. Somehow, GCC doesn't complain at all. However, looking at generated assembly code, GCC produces wrong code for calling bar, and vvvvvv is linked correctly though. 0000000000400510 <foo>: 400510: 48 83 ec 08 sub $0x8,%rsp 400514: 89 fe mov %edi,%esi 400516: 31 c0 xor %eax,%eax 400518: bf 1c 06 40 00 mov $0x40061c,%edi 40051d: e8 56 01 00 00 callq 400678 <pri...@plt> 400522: 31 c0 xor %eax,%eax 400524: e8 d7 fa bf ff callq 0 <__fini_array_end> <-------- should call bar. 400529: 8b 05 a1 17 00 00 mov 0x17a1(%rip),%eax # 401cd0 <vvvvvv> 40052f: 48 83 c4 08 add $0x8,%rsp 400533: 05 e8 03 00 00 add $0x3e8,%eax 400538: c3 retq 400539: 0f 1f 80 00 00 00 00 nopl 0x0(%rax) Is this a bug? GCC should issue warning/error here. Why is vvvvvv linked correctly? Shouldn't it be treated as static with -fwhile-program and without externally_visible? My trunk is 160104 by the way. Thanks, Bingfeng > -----Original Message----- > From: Jan Hubicka [mailto:hubi...@ucw.cz] > Sent: 27 May 2010 09:04 > To: Richard Guenther > Cc: Bingfeng Mei; gcc@gcc.gnu.org > Subject: Re: externally_visible and resoultion file > > > On Wed, May 26, 2010 at 5:53 PM, Bingfeng Mei <b...@broadcom.com> > wrote: > > > Hi, Richard, > > > With resolution file generated by GOLD (or I am going to hack gnu > LD), is > > > externally_visible attribute still needed to annotate those symbols > accessed > > > from non-LTO objects when compiling with -fwhole-program. > > > > Yes it is. We do not parse the complete resolution file but only the > > entries we'll end up reading .o files with LTO information for. > > > > > In theory, it shouldn't be needed since LTO has all information. > But what > > > about current implementation. I checked relevant source files and > can't > > > get immediate clue. > > > > The current implementation has no idea of the external references > > (though it's probably not too hard to implement). > > Yep, this is also one of my TODO list items... > > Honza > > > > Richard.