RFR: 8256594: Unexpected warning: SIGSEGV handler flags expected:SA_RESTART|SA_SIGINFO found:SA_RESTART|SA_SIGINFO

[Thomas Stuefe]

On Thu, 19 Nov 2020 07:45:03 GMT, David Holmes <dholmes at openjdk.org> wrote:

> In the recent POSIX signal code cleanup (JDK-8253742) I misunderstood the role of the SIGNIFICANT_SIGNAL_MASK and removing its application causes -Xcheck:jni to report errors with the signal handler due to an unexpected bit in the sigaction.sa_flags field.
> 
> This fix restores the masking of that flag, for Linux only, and more clearly indicating what it is. I also augmented the flag printing code to show when an unexpected flag is present (and so avoid the mysterious "expected X found X" message).
> 
> See bug report for more details.
> 
> Thanks.

LGTM.

Note that a maybe more elegant approach - avoiding the double definition of known flags - would have been, in the print loop, to store the checked flags in a mask. And then test for ~mask at the final step.

The numeric comparison of flags in check_jni - which requires this SA_RESTORER_FLAG_MASK workaround - is a bit grating. Would have been better to compare just known flags. But this is old coding.

All idle nitpicking :) Patch is fine.

..Thomas

src/hotspot/os/posix/signals_posix.cpp line 668:

> 666:   strncpy(buffer, "none", size);
> 667: 
> 668:   const unsigned int unknown_flag = ~(SA_NOCLDSTOP |

Maybe name this "unknown_flag_mask" ?

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Marked as reviewed by stuefe (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1309