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Re: [PATCH] S390: Fix backtrace in vdso functions.
- From: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- To: libc-alpha at sourceware dot org
- Date: Tue, 28 Nov 2017 11:09:10 -0200
- Subject: Re: [PATCH] S390: Fix backtrace in vdso functions.
- Authentication-results: sourceware.org; auth=none
- References: <ead922fd-1eb9-3781-345d-6a2ea63ecd01@linux.vnet.ibm.com>
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>