arm: Update _dl_tlsdesc_dynamic to preserve caller-saved registers (BZ 31372)

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>

1 files changed, 15 insertions, 0 deletions

diff --git a/sysdeps/arm/configure.ac b/sysdeps/arm/configure.ac
index 5172e30bbe..cd00ddc9d9 100644
--- a/sysdeps/arm/configure.ac
+++ b/sysdeps/arm/configure.ac
@@ -21,6 +21,21 @@ else
   LIBC_CONFIG_VAR([default-abi], [soft])
 fi
 
+AC_CACHE_CHECK([whether VFP supports 32 registers],
+		libc_cv_arm_pcs_vfp_d32, [
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
+void foo (void)
+{
+  asm volatile ("vldr d16,=17" : : : "d16");
+}
+]])],
+                [libc_cv_arm_pcs_vfp_d32=yes],
+                [libc_cv_arm_pcs_vfp_d32=no])])
+if test "$libc_cv_arm_pcs_vfp_d32" = yes ;
+then
+  AC_DEFINE(HAVE_ARM_PCS_VFP_D32)
+fi
+
 AC_CACHE_CHECK([whether PC-relative relocs in movw/movt work properly],
 	       libc_cv_arm_pcrel_movw, [
 cat > conftest.s <<\EOF