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Re: PING^1: [PATCH 1/2] Mark internal mmap functions hidden in

On Wed, Jan 6, 2016 at 10:34 AM, Adhemerval Zanella
<> wrote:
> Checking of the dissassemble for i686 I see no PLT stub
> being generated for mmap or it being called through it:
> $ objdump -d elf/
> [...]
>     5cdc:       89 04 24                mov    %eax,(%esp)
>     5cdf:       e8 fc 49 01 00          call   1a6e0 <__mmap>
> [...]
> Also regarding mmap I see that generated assembly generated is
> not different without the patch. I do see that for the part 02
> of the patch for the __libc_{open,close} with the patch a
> call to __x86.get_pc_thunk.bx is removed (which is the intention
> of the patch).
> Am I missing something here?

Since __mmap is local in /lib/

   329: 00019370    86 FUNC    LOCAL  DEFAULT   11 __mmap

linker won't use PLT.  But since we don't tell GCC about it,
GCC will assume PLT is used:

000052a5  00023e04 R_386_PLT32            00000000   __mmap

which reserves EBX for PLT.  With my patch, you will see

000052a5  00023e04 R_386_PC32           00000000   __mmap

which frees EBX for other use.


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