Re: Visibility=hidden for x86_64 Xen builds -- problems?
On 28/9/06 14:24, "H. J. Lu" <[EMAIL PROTECTED]> wrote: > On Thu, Sep 28, 2006 at 10:45:38AM +0100, Jan Beulich wrote: >> >> 2) Why does the linker silently resolve the (32-bit PC-relative) >> relocation targeting an undefined weak symbol, yielding at >> run-time a non-zero address? While I can see the point of > > Do you have a testcase? I can't reproduce it. If it is true, I consider > it a linker bug. Compile and link the attached C program as follows. I used gcc-4.1.1 and binutils-2.17, but gcc >= 4.0.0 and binutils >= 2.16 probably suffice. # gcc -fpic -o test.o -c test.c # ld -Ttext 1 -o test test.o Disassembly of the result trivially shows that the address of weak symbol 'x' is 0x1. -- Keir test.c Description: Binary data
Re: Visibility=hidden for x86_64 Xen builds -- problems?
> Compile and link the attached C program as follows. I used gcc-4.1.1 and > binutils-2.17, but gcc >= 4.0.0 and binutils >= 2.16 probably suffice. > > # gcc -fpic -o test.o -c test.c > # ld -Ttext 1 -o test test.o > > Disassembly of the result trivially shows that the address of weak symbol 'x' > is 0x1. By the way, experimentation with the address of the text section shows that the weak symbol's address is resolved to the nearest 4GB-aligned address (nearest to what I'm not sure -- RIP? Section start?). It may get rounded up or down, whichever is nearest. -- Keir
Re: [discuss] Re: Visibility=hidden for x86_64 Xen builds -- problems?
On 29/9/06 1:40 am, "H. J. Lu" <[EMAIL PROTECTED]> wrote: > You are asking for impossible: If the compiler emitted accesses via the GOT for weak symbols then there wouldn't be a problem. The compiler doesn't know the final link address though, so it'd have to be conservative. Perhaps it's not worth it for a case that noone much cares about. > R_X86_64_PC32 only supports signed 32bit offset. 0x1 is more > than 32bit. The linker should issue an error, at least a warning. You > can take your pick and I will fix the linker. If no one objects, I > will make it an error. That's fine with us. I fixed Xen to no longer use weak symbols. -- Keir
