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Re: [PATCH] S390: Fix backtrace in vdso functions.
- From: Stefan Liebler <stli at linux dot vnet dot ibm dot com>
- To: libc-alpha at sourceware dot org
- Date: Mon, 4 Dec 2017 08:59:47 +0100
- Subject: Re: [PATCH] S390: Fix backtrace in vdso functions.
- Authentication-results: sourceware.org; auth=none
- References: <email@example.com> <firstname.lastname@example.org>
On 11/28/2017 02:09 PM, Adhemerval Zanella wrote:
On 28/11/2017 10:44, Stefan Liebler wrote:
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).
(INTERNAL_VSYSCALL_CALL, CLOBBER_0, CLOBBER_1, CLOBBER_2,
CLOBBER_3, CLOBBER_4, CLOBBER_5, CLOBBER_6,
* sysdeps/unix/sysv/linux/s390/s390-32/sysdep.h: Likewise.
Reviewed-by: Adhemerval Zanella <email@example.com>
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?