[llvm-dev] [PPC] Linker fails on -fstack-protector

[Eric Christopher via llvm-dev]

On Wed, Feb 10, 2016 at 5:04 PM Hal Finkel <hfinkel at anl.gov> wrote:

>
> ------------------------------
>
> *From: *"Eric Christopher" <echristo at gmail.com>
> *To: *"Tim Shen" <timshen at google.com>, llvm-dev at lists.llvm.org, "Hal
> Finkel" <hfinkel at anl.gov>, "Kit Barton" <kbarton at ca.ibm.com>
> *Sent: *Wednesday, February 10, 2016 6:59:50 PM
> *Subject: *Re: [llvm-dev] [PPC] Linker fails on -fstack-protector
>
>
>
>
>
> On Mon, Jan 25, 2016 at 11:58 AM Tim Shen via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> When -fstack-protector is turned on, linker fails to find the symbol "__stack_chk_guard"
>> because at least for powerpc64le, glibc doesn't provide this symbol.
>> Instead, they put the stack guard into TCB.
>>
>> x86 fixed this issue by injecting a special address space (which is later
>> translated to TCB register access) and hard code the offset of stack_guard,
>> but I don't see a easy way to handle address spaces in ppc.
>>
>
>
> Why is handling address spaces in ppc any more difficult than doing so for
> x86?
>

Shouldn't be at all, mostly just seems that a bunch of it hasn't been set
up yet.

-eric


>
>  -Hal
>
>
>> A cleaner solution could be adding an IR intrinsic llvm.get_tcb_address()
>> and hard code the offset of stack_guard member, since they aren't supposed
>> to change.
>>
>> Details are in the bug: https://llvm.org/bugs/show_bug.cgi?id=26226
>>
>> Any ideas?
>>
>>
> Not a huge fan of a ppc specific intrinsic (which it should be, so
> llvm.ppc... if we go that route) to do this. I actually rather liked the
> cleanliness of the address space solution for x86. How much work would it
> be to do that? Alternately: Hal, Kit, what do you two think as far as the
> ppc backend?
>
> The other solution you mentioned - combining the slot load into the
> existing intrinsic might work, we'd just need to figure out how to
> autoupgrade everything into it which might be a bit more difficult than
> fixing the backends and dealing. Have you looked into how the autoupgrade
> would work?
>
> Thanks!
>
> -eric
>
>
>> Thanks!
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>
>
>
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
>
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