On 20.07.22 15:01, Alexander Monakov wrote:
On Wed, 20 Jul 2022, Sebastian Huber wrote:
On 20/07/2022 13:41, Alexander Monakov wrote:
On Wed, 20 Jul 2022, Sebastian Huber wrote:
How does Ada get its default TLS model?
You shouldn't need to do anything special, GCC automatically selects
initial-exec or local-exec for non-PIC (including PIE).
I am not sure, for this test program:
extern _Thread_local int i;
_Thread_local int j;
int f(void)
{
return i + j;
}
I get:
[snip]
Thanks, I missed that you are asking about promoting initial-exec to local-exec
rather than x-dynamic to y-exec. There's a pending patch that implements such
promotion based on visibility information:
https://gcc.gnu.org/pipermail/gcc-patches/2022-July/598017.html
With that patch, you'll get local-exec model for the extern variable 'i' if you
inform the compiler that its definition will end up in the current module:
__attribute__((visibility("hidden")))
extern _Thread_local int i;
_Thread_local int j;
int f(void)
{
return i + j;
}
Thus I would try to enhance the binds_local_p target hook for RTEMS to inform
the compiler that there's no dynamic linking (although apart from TLS variables
I cannot instantly name other places where it would enhance optimization).
This sounds like an interesting approach in the long run, however, I
need a short term solution which I can back port to GCC 10, 11, and 12.
I guess I will add a
MULTILIB_EXTRA_OPTS = ftls-model=local-exec
to all RTEMS multilib configurations.
In general I think the target hooks are hard to customize for operating
systems.
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