s390/unwind: make reuse_sp default when unwinding pt_regs

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Currently unwinder yields 2 entries when pt_regs are met:
sp="address of pt_regs itself" ip=pt_regs->psw
sp=pt_regs->gprs[15] ip="r14 from stack frame pointed by pt_regs->gprs[15]"

And neither of those 2 states (combination of sp and ip) ever happened.

reuse_sp has been introduced by commit a1d863ac3e ("s390/unwind: fix
mixing regs and sp"). reuse_sp=true makes unwinder keen to produce the
following result, when pt_regs are given (as an arg to unwind_start):
sp=pt_regs->gprs[15] ip=pt_regs->psw
sp=pt_regs->gprs[15] ip="r14 from stack frame pointed by pt_regs->gprs[15]"

The first state is an actual state in which a task was when pt_regs were
collected. The second state is marked unreliable and is for debugging
purposes to cover the case when a task has been interrupted in between
stack frame allocation and writing back_chain - in this case r14 might
show an actual caller.

Make unwinder behaviour enabled via reuse_sp=true default and drop the
special case handling.

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

...

This commit is contained in:

Vasily Gorbik 2019-11-22 15:58:42 +01:00

parent 67f5593419

commit 97806dfb6f

2 changed files with 7 additions and 15 deletions

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1

arch/s390/include/asm/unwind.h

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21

arch/s390/kernel/unwind_bc.c

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