Re: [discuss] Re: Visibility=hidden for x86_64 Xen builds -- problems?

["H. J. Lu" <hjl at lucon dot org>]

On Thu, Sep 28, 2006 at 03:33:05PM +0100, Keir Fraser wrote:
> 
> > 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 100000000 -o test test.o
> > 
> > Disassembly of the result trivially shows that the address of weak symbol 'x'
> > is 0x100000000.
> 
> 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.

You are asking for impossible:

[hjl@gnu-13 weak-4]$ objdump -dr foo.o

foo.o:     file format elf64-x86-64

Disassembly of section .text:

0000000000000000 <_start>:
   0:   55                      push   %rbp
   1:   48 89 e5                mov    %rsp,%rbp
   4:   48 8d 05 00 00 00 00    lea    0(%rip),%rax        # b
<_start+0xb>
                        7: R_X86_64_PC32        x+0xfffffffffffffffc
   b:   c9                      leaveq
   c:   c3                      retq

R_X86_64_PC32 only supports signed 32bit offset. 0x100000000 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.


H.J.