----- On Aug 6, 2018, at 7:47 AM, gor gor@linux.ibm.com wrote:
While implementing rseq selftest for s390 a glibc problem with tls variables alignment has been discovered. It turned out to be a general problem affecting several architectures. The bug opened for this problem:
https://sourceware.org/bugzilla/show_bug.cgi?id=23403
There is no fix yet. On s390 __rseq_abi ends up aligned to 0x10 instead of 0x20 which makes rseq selftest fail every time.
The change proposed adds __rseq_abi misalignment check, produces user friendly message and skips the test.
That's a very unfortunate situation. I'm concerned about adding glibc-specific error messages in rseq selftests though. I'm curious to hear what others think about this.
I would have thought simply improving rseq registration error handling from having the test program return nonzero to add a perror() in there would be a more generic way to handle this.
Regarding the message printed by your check: "you need a fixed version of glibc to run this test". I disagree with it. Someone can effectively run the test on a bogus glibc and it serves its purpose: it reports that glibc is buggy.
I would understand adding this kind of test in an user-facing application or library to detect bogus glibc (in fact I've used similar approaches in lttng-ust to detect bogus compilers), but why add this to skip a selftest program, which sole purpose is to test the stack underneath it ?
Thanks,
Mathieu
Vasily Gorbik (1): rseq/selftests: add __rseq_abi misalignment check
tools/testing/selftests/rseq/rseq.c | 19 +++++++++++++++++++ .../testing/selftests/rseq/run_param_test.sh | 4 ++-- 2 files changed, 21 insertions(+), 2 deletions(-)
-- 2.18.0.13.gd42ae10