Re: [PATCH] x86-64: Align the stack in __tls_get_addr [BZ #21609]

[Florian Weimer <fweimer at redhat dot com>]

On 07/06/2017 05:32 PM, Alexander Monakov wrote:
> On Thu, 6 Jul 2017, Alexander Monakov wrote:
>> There is no need to introduce new symbols nor symbol versions. It's
>> sufficient to implement amd64 __tls_get_attr in assembly, rename generic
>> __tls_get_attr, and call the renamed generic implementation from the slow
>> path after realigning the stack.
> 
> Actually, looking at elf/dl-tls.c, I see that __tls_get_addr doesn't need
> aligned stack, and its callees update_get_addr and tls_get_addr_tail are
> already marked noinline, so isn't it sufficient to additionally mark those
> with __attribute__((force_align_arg_pointer)) on x86-64?

I'm not sure if GCC will honor force_align_arg_pointer on a static
function which provably called with a properly aligned stack only.  We'd
need another attribute on __tls_get_addr to tell GCC that it is called
with a misaligned stack pointer.

Thanks,
Florian