[PATCH] S390: Fix backtrace in vdso functions.

[Adhemerval Zanella]

On 28/11/2017 10:44, Stefan Liebler wrote:
> Hi,
> 
> On s390, GDB fails to show the complete backtrace from within vdso functions. The macro INTERNAL_VSYSCALL_CALL saves the return address in r14 to r10 before branching to the vdso function. The branch-instruction updates r14 in order to let the vdso function return. Then the original address in r14 is restored from r10. Unfortunately, there are no cfi-rules and GDB fails.
> 
> Furthermore the call of the vdso function does not comply with the s390 ABI as no stack-frame for the vdso-function is generated.
> 
> This patch removes the s390 specific macro INTERNAL_VSYSCALL_CALL and the common implementation in sysdeps/unix/sysv/linux/sysdep-vdso.h is used. Then the vdso function is called via function-pointer and GCC generates a new stack-frame and emits all needed cfi-rules.
> 
> The defines CLOBBER_[0-6] are removed as they  were only used in macro INTERNAL_VSYSCALL_CALL.
> 
> The macro INTERNAL_VSYSCALL_NO_SYSCALL_FALLBACK is not used on s390. The only user is power. Thus it is removed from s390 sysdep.h.

I am almost sure we can remove it for powerpc as well (I can't see
no immediate gain on doing a function call using inline assembly
as for INTERNAL_VSYSCALL_NO_SYSCALL_FALLBACK on powerpc). 


> 
> ChangeLog:
> 
> Â Â Â Â * sysdeps/unix/sysv/linux/s390/s390-64/sysdep.h
> Â Â Â Â (INTERNAL_VSYSCALL_CALL, CLOBBER_0, CLOBBER_1, CLOBBER_2,
> Â Â Â Â  CLOBBER_3, CLOBBER_4, CLOBBER_5, CLOBBER_6,
> Â Â Â Â INTERNAL_VSYSCALL_NO_SYSCALL_FALLBACK): Remove.
> Â Â Â Â * sysdeps/unix/sysv/linux/s390/s390-32/sysdep.h: Likewise.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>