On Wed, May 20, 2015 at 8:13 AM, Lynn A. Boger
<labo...@linux.vnet.ibm.com> wrote:
>
>
> On 05/19/2015 07:52 PM, Alan Modra wrote:
>>
>> On Tue, May 19, 2015 at 07:40:15AM -0500, Lynn A. Boger wrote:
>>>
>>> Questions on the use of the options for split stack:
>>>
>>> - The way this is implemented, split stack is generated if the
>>> target platform supports split stack, on ppc64/ppc64le as well
>>> as on x86, and the use of -fno-split-stack doesn't seem to affect it
>>> for any of these. Is that the way it should work? I would expect
>>> -fno-split-stack to disable it completely.
>>
>> Can you give a testcase to show what you mean? Picking one of the go
>> testsuite programs at random, I see
>> $ gcc/xgcc -Bgcc/ -S -I powerpc64le-linux/libgo
>> /src/gcc-virgin/gcc/testsuite/go.test/test/args.go
>> $ grep morestack args.s
>> bl __morestack
>> bl __morestack
>> $ gcc/xgcc -Bgcc/ -fno-split-stack -S -I powerpc64le-linux/libgo
>> /src/gcc-virgin/gcc/testsuite/go.test/test/args.go
>> $ grep morestack args.s
>> $
>> That shows -fno-split-stack being honoured.
>
> You are correct. I made some mistake in my testing.
>>>
>>> - The comments say that the gold linker is used for some
>>> situations but I don't see any reference in the code to enabling
>>> the gold linker for ppc64le, ppc64, or x86. Is the user expected
>>> to add the option for the gold linker if needed?
>>
>> At the moment I believe this is true.
>
>
> I have been trying to use the gold linker with your patch and seems to work
> fine. I added the following to
> the STACK_SPLIT_SPEC in gcc/gcc.c to enable the gold linker if -fsplit-stack
> is set, but that will cause problems
> on systems where the gold linker (and the correct level of binutils for
> Power) is not available. Is this an
> absolute requirement to use split stack? Could the configure determine if
> gold is available and
> generate this one way or another?
>
> --- gcc.c (revision 223217)
> +++ gcc.c (working copy)
> @@ -541,7 +541,8 @@ proper position among the other output files. */
> libgcc. This is not yet a real spec, though it could become one;
> it is currently just stuffed into LINK_SPEC. FIXME: This wrapping
> only works with GNU ld and gold. */
> -#define STACK_SPLIT_SPEC " %{fsplit-stack: --wrap=pthread_create}"
> +#define STACK_SPLIT_SPEC \
> + " %{fsplit-stack: --wrap=pthread_create -fuse-ld=gold}"
>
> #ifndef LIBASAN_SPEC
> #define STATIC_LIBASAN_LIBS \
Lynn,
split-stack does not require Gold linker. This is a non-starter.
Gold is necessary for some corner cases of mixing split-stack and
non-split-stack modules.
- David
