ARM _dl_tlsdesc_dynamic slow path has two issues:
* The ip/r12 is defined by AAPCS as a scratch register, and gcc is
used to save the stack pointer before on some function calls. So it
should also be saved/restored as well. It fixes the tst-gnu2-tls2.
* None of the possible VFP registers are saved/restored. ARM has the
additional complexity to have different VFP bank sizes (depending of
VFP support by the chip).
The tst-gnu2-tls2 test is extended to check for VFP registers, although
only for hardfp builds. Different than setcontext, _dl_tlsdesc_dynamic
does not have HWCAP_ARM_IWMMXT (I don't have a way to properly test
it and it is almost a decade since newer hardware was released).
With this patch there is no need to mark tst-gnu2-tls2 as XFAIL.
Checked on arm-linux-gnueabihf.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
