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Re: [PATCH] S390: Fix backtrace in vdso functions.


On 11/28/2017 02:09 PM, Adhemerval Zanella wrote:


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:

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

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


If there are no objections regarding the s390 patch, I'll commit.

Adhemerval: Do you keep working on removing INTERNAL_VSYSCALL_NO_SYSCALL_FALLBACK on powerpc?

Bye.
Stefan


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