S390: Add cfi information for start routines in order to stop unwinding

System Internals / glibc - Stefan Liebler [linux.vnet.ibm.com] - 21 November 2017 07:45 EST

GDB failed to detect the outermost frame while showing the backtrace within a thread: Backtrace stopped: previous frame identical to this frame (corrupt stack?)

Before this patch, the start routines like thread_start had no cfi information. GDB is then using the prologue unwinder if no cfi information is available. This unwinder tries to unwind r15 and stops e.g. if r15 was updated or on some jump-instructions.

On older glibc-versions (before commit "Remove cached PID/TID in clone" c579f48edba88380635ab98cb612030e3ed8691e), the thread_start function used such a jump-instruction and GDB did not fail with an error.

This patch adds cfi information for _start, thread_start and __makecontext_ret and marks r14 as undefined which marks the frame as outermost frame and GDB stops the backtrace. Also tested different gcc versions in order to test _Unwind_Backtrace() in libgcc as this is used by backtrace() in glibc.


- sysdeps/s390/s390-64/start.S (_start): Add cfi information for r14.
- sysdeps/s390/s390-32/start.S: (_start): Likewise
- sysdeps/unix/sysv/linux/s390/s390-64/clone.S (thread_start): Likewise.
- sysdeps/unix/sysv/linux/s390/s390-32/clone.S (thread_start): Likewise.
- sysdeps/unix/sysv/linux/s390/s390-64/__makecontext_ret.S (__makecontext_ret): Likewise.
- sysdeps/unix/sysv/linux/s390/s390-32/__makecontext_ret.S (__makecontext_ret): Likewise.

8beba15d53 S390: Add cfi information for start routines in order to stop unwinding.
ChangeLog | 13 +++++++++++++
sysdeps/s390/s390-32/start.S | 7 +++++++
sysdeps/s390/s390-64/start.S | 7 +++++++
sysdeps/unix/sysv/linux/s390/s390-32/__makecontext_ret.S | 10 ++--------
sysdeps/unix/sysv/linux/s390/s390-32/clone.S | 4 ++++
sysdeps/unix/sysv/linux/s390/s390-64/__makecontext_ret.S | 10 ++--------
sysdeps/unix/sysv/linux/s390/s390-64/clone.S | 4 ++++
7 files changed, 39 insertions(+), 16 deletions(-)

Upstream: sourceware.org

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