Re: unaligned access using bash on glibc 2.5

Carlos O'Donell a écrit :
> On 5/1/07, John David Anglin <[email protected]> wrote:
>> The two least significant bits in ip contain the priviledge level
>> of the executing code.  They have to be masked off to get the address
>> of a faulting instruction.
> 
> You'll be pleasantly suprised to know we tracked this down to a
> missing save/restore of the PIC register on a library call.
> 
>   0x40bcb744 <closedir+44>:       copy r20,r22
>   0x40bcb748 <closedir+48>:       b,l 0x40bb4aa0,rp
>   0x40bcb74c <closedir+52>:       copy r3,r26
> 
> See this lonely b,l without a PIC register save/restore? That's the
> problem. It's a jump to a stub, which calls free, but free tailcalls
> into __internal_free, and the PIC register isn't restored by free or
> by closedir.
> 
> FWIW I see this aswell when compiling glibc with gcc mainline:
> 
>   10:   6b d3 3f c1     stw r19,-20(sp)
> ../sysdeps/unix/closedir.c:52
>   14:   e8 40 00 00     b,l 1c <__closedir+0x1c>,rp
>                         14: R_PARISC_PCREL17F   free
>   18:   0c a0 10 85     ldw 0(r5),r5
> ../sysdeps/unix/closedir.c:54
>   1c:   08 05 02 5a     copy r5,r26
>   20:   08 13 02 44     copy r19,r4
> 
> Why isn't there a save/restore of the PIC register around the call to
> free? Clearly r19 is being used, notice the save/restore starting on
> "20:".
> 

In case you want to have a closer look, please find attached the
preprocessed file. I will try to reduce the testcase later today.

The problem does not appear at -O0, and start to appears with -O1.

Cheers,
Aurelien

-- 
  .''`.  Aurelien Jarno	            | GPG: 1024D/F1BCDB73
 : :' :  Debian developer           | Electrical Engineer
 `. `'   [email protected]         | [email protected]
   `-    people.debian.org/~aurel32 | www.aurel32.net

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