(At least on x86(_32),) `unw_resume` will call `setcontext` which will modify the signal masks
based on the value in the context. Since the signal mask is not being initialized by
`unw_getcontext`, this cause the signal mask to be set to a random (uninitialized) value after
`unw_resume` which cause the test to fail since it relies on the signal mask for SIGUSR2 being
cleared.
The proper fix is likely to either make `unw_resume` not touch the signal mask if the context
wasn't initialized with a signal ucontext, or to make `unw_getcontext` record the signal mask too.
It's unclear to me which approach should be taken...
In the mean time, the intermittent failure can be fixed simply by zero initialing the context first
which would clear all the signal masks.
When siginfo is available, a more reliable way is to use the `ucontext` passed in
to the signal handler directly and rely on `sigreturn` to reset it.
Unfortunately, this is currently not implemented on all archs either.
Currently setcontext for x86_64 restores the signal mask, even
though it is never saved anywhere. This means the signal mask
is often garbage after an unw_resume.
(changed in commit f8a15e9679)
It looks like this was a fix for the Gtest-resume-sig function -
testing if signal masks are restored across signal frames. The
root issue looks like that x86_64 only uses sigreturn for the exact
signal frame, and not for any decedant frames as well (as i64 does).
Instead, modify Gresume to use sigreturn if *any* frame on the stack
is a signal frame, so that we correct fixup the signal mask and any
sigaltstacks. The sigreturn os-specific functions are changed slightly
to copy in the saved ucontext structure if we are jumping farther
up the stack.
This should fix sigprocmask reported issues such as
https://github.com/dropbox/pyston/blob/master/libunwind_patches/0002-pyston-stop-x86_64-setcontext-restoring-uninitialize.patch
Tests pass on freebsd, linux
Introduce a new test case that is derived from test-resume-sig, but
using the SA_SIGINFO sigaction() flag. This case is referred in the
linux kernel sources as "realtime" signal handler, and is handled
differently in the kernel on many architectures and in libunwind as
well.
Compiling the tests with -Wextra results to lots of warnings for unused
parameters. Annotate these cases with the `unused' attribute to avoid
the warnings.
(main): Do some silly FP computations. On x86-64, this ensures
that the signal handler invocations will always be called
with the FPU-state saved as well. Without this, the first
signal was invoked without FPU-state, the second with, causing
a spurious failure.
2004/11/17 02:06:25-08:00 mostang.com!davidm
(get_bsp): New function.
(handler): Clean up & check for error returns.
(main): Also fail if we didn't get SIGUSR2.
(Logical change 1.290)
