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Re: [PATCH] ARM: Add pointer guard support.


> On Sep 25, 2013, at 9:09 AM, "Carlos O'Donell" <carlos@redhat.com> wrote:
> 
>> On 09/25/2013 05:06 AM, Will Newton wrote:
>> 
>> Add support for pointer mangling in glibc internal structures in C
>> and assembler code.
>> 
>> Tested on armv7 with hard and soft thread pointers.
> 
> Have you measured the performance versus using the existing
> global variable? 
> 
> TLS access on ARM is quite slow and it looks to me like it 
> may be faster to use the global variable. Keep in mind that
> the pointer guard and stack guard do not vary by thread.
> 
> 32-bit ARM is currently using a global variable e.g.
> __pointer_chk_guard, all you need to do to make it work
> is adjust the definitions of PTR_MANGLE and PTR_DEMANGLE
> to reference the global symbol.
> 
> This is the second proposal for ARM (first was [1] for
> AArch64) to support storing the a guard in the TCB, but
> nobody has responded yet to my question about performance.
T 
I wonder the same question.  Why move to using to tcb in the first place.  The only answer I can figure out is that is what x86 does but that is not always the correct answer.

> 
> Cheers,
> Carlos.
> 
> [1] https://sourceware.org/ml/libc-ports/2013-08/msg00052.html
> 


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