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

[Tim Shen via llvm-dev]

I'll come up with a address-space-based proof of concept.

On Wed, Feb 10, 2016, 17:05 Eric Christopher <echristo at gmail.com> wrote:

> 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!
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>
>>
>>
>> --
>> Hal Finkel
>> Assistant Computational Scientist
>> Leadership Computing Facility
>> Argonne National Laboratory
>>
>
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