[PATCH 2/X, i386, PR54232] Enable EBX for x86 in 32bits PIC code

[Evgeny Stupachenko]

What if we remove the check?
glibc build pass?

On Sat, Oct 25, 2014 at 3:09 AM, Andrew Pinski <pinskia@gmail.com> wrote:
> On Fri, Oct 10, 2014 at 12:43 AM, Evgeny Stupachenko <evstupac@gmail.com> wrote:
>> i386 specific part of the patch:
>>
>> 2014-10-08  Ilya Enkovich  <ilya.enkovich@intel.com>
>>             Vladimir Makarov  <vmakarov@redhat.com>
>>         * gcc/config/i386/i386.c (ix86_use_pseudo_pic_reg): New.
>>         (ix86_init_pic_reg): New.
>>         (ix86_select_alt_pic_regnum): Add check on pseudo register.
>>         (ix86_save_reg): Likewise.
>>         (ix86_expand_prologue): Remove irrelevant code.
>>         (ix86_output_function_epilogue): Add check on pseudo register.
>>         (set_pic_reg_ever_alive): New.
>>         (legitimize_pic_address): Replace df_set_regs_ever_live with new
>>         set_pic_reg_ever_alive.
>>         (legitimize_tls_address): Likewise.
>>         (ix86_pic_register_p): New check.
>>         (ix86_delegitimize_address): Add check on pseudo register.
>>         (ix86_expand_call): Insert move from pseudo PIC register to ABI
>>         defined REAL_PIC_OFFSET_TABLE_REGNUM.
>>         (TARGET_INIT_PIC_REG): New.
>>         (TARGET_USE_PSEUDO_PIC_REG): New.
>>         (PIC_OFFSET_TABLE_REGNUM): New check.
>
>
> This patch breaks glibc's ld.so on i686.
> glibc has a check to make sure the PIC register is setup correctly:
> /* Consistency check for position-independent code.  */
> #ifdef __PIC__
> # define check_consistency()      \
>   ({ int __res;      \
>      __asm__ __volatile__      \
>        (LOAD_PIC_REG_STR (cx) ";"      \
> "subl %%ebx, %%ecx;"      \
> "je 1f;"      \
> "ud2;"      \
> "1:\n"      \
> : "=c" (__res));      \
>      __res; })
> #endif
>
> This depends on ebx being the PIC register.  Now we don't have this so
> we get ud2 in some cases.
>
>
>
> Thanks,
> Andrew Pinski