Use -ftls-model=local-exec for RTEMS by default?

[Iain Sandoe]

> On 22 Jul 2022, at 12:19, Sebastian Huber <sebastian.huber@embedded-brains.de> wrote:
> 
> On 21.07.22 10:03, Iain Sandoe wrote:
>>> 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.
>> (IMO) It can be not too tricky -  Darwin customises several - you just have to override the default definition in your target-specific header and provide the replacement e.g ( override in config/darwin.h, replacement in config/darwin.cc):
>> #undef TARGET_ENCODE_SECTION_INFO
>> #define TARGET_ENCODE_SECTION_INFO  darwin_encode_section_info
> 
> The problem is that in this case you need a target-specific copy and paste solution. For example lets suppose you want to use
> 
> #define CC1_SPEC "%{!ftls-model=*:-ftls-model=local-exec}"
> 
> for RTEMS (in gcc/config/rtems.h), then you have a problem on for example microblaze (gcc/config/microblaze/microblaze.h):
> 
> #ifndef CC1_SPEC
> #define CC1_SPEC " \
> %{G*} \
> %(subtarget_cc1_spec) \
> %{mxl-multiply-high:-mcpu=v6.00.a} \
> "
> #endif
> 
> or nios2 (gcc/config/nios2/nios2.h):
> 
> #define CC1_SPEC "%{G*}"
> 
> For each target you would have to check if you have to provide some extra times for CC1_SPEC through copy and paste.

Yes, there is a curious ‘inversion’ process where, to the OS, the architectures are sub-targets, but to the GCC implementation the OSs are sub-targets of the arch, it can be possible to work around this by declaring SUBTARGET_SPEC_XXXX and then appending that to the various users.  However, it could be that even that will not work easily in this case.
Iain