On Fri, Jun 9, 2017 at 11:22 AM, Jan Hubicka <hubicka@ucw.cz> wrote:
>> On Fri, Jun 9, 2017 at 3:16 AM, Jan Hubicka <hubicka@ucw.cz> wrote:
>> >
>> >> code compiled with -fsplit-stack, if the cold partition calls a
>> >> function that is not compiled with -fsplit-stack (such as a C library
>> >> function).  The problem is that when the linker sees a split-stack
>> >> function call a non-split-stack function, it adjusts the function
>> >> header to request more stack space.  This doesn't work if the call is
>> >> in the cold partition, as the linker doesn't know how to find the
>> >> header to adjust.  You can see this by trying to build the Go library
>> >> using the gold linker with this patch.
>> >
>> > If code does not work, I wonder why we let user to overwrite the default
>> > by hand? In other cases we drop the flag with inform message.
>>
>> My thinking here is that there is no fundamental reason that the code
>> does not work, and the actual problem does not lie in GCC but rather
>> in the linker (specifically, gold).  It's possible in principle to fix
>> gold to make this work, and someone who is using a fixed gold could
>> then direct GCC to take advantage of this optimization (and later
>> after that version of gold is wide-spread enough we can change GCC to
>> drop this patch).
>
> Thanks for explanation.  Perhaps we could have this documented, because
> otherwise people will think the option is simply broken. I guess even better
> we could have configure autodetection for the broken linker.

Committed to mainline with docs as follows.

Ian