On Apr 3 23:09, Jon TURNEY wrote: > On 01/04/2015 15:22, Corinna Vinschen wrote: > >On Apr 1 14:19, Jon TURNEY wrote: > >>Add ucontext.h header, defining ucontext_t and mcontext_t types. > >> > >>Provide sigaction sighandlers with a ucontext_t parameter, containing stack > >>and > >>context information. > >> > >> * include/sys/ucontext.h : New header. > >> * include/ucontext.h : Ditto. > >> * exceptions.cc (call_signal_handler): Provide ucontext_t > >> parameter to signal handler function. > > > >Patch is ok with a single change: Please add a "FIXME?" comment to: > > > > else > > RtlCaptureContext(); > > > >On second thought, calling RtlCaptureContext here is probably wrong. > > Wrong and also dangerous. > > This causes random crashes on x86. > > It seems that RtlCaptureContext requires the framepointer of the calling > function in ebp, which it uses to report the rip and rsp of it's caller. > > It also seems that gcc can decide to optimize the setting of the > framepointer away, irrespective of the fact that -fomit-frame-pointer is not > used when building exceptions.cc > > If _cygtls::call_signal_handler() happens to get called with ebp pointing to > an invalid memory address, as seems to happen occasionally, we will fault in > RtlCaptureContext. (in all cases, the eip and ebp in the returned context > are incorrect) > > I wrote the attached patch, which fakes a callframe for RtlCaptureContext to > avoid these possible crashes, but this needs more work to correctly report > eip and ebp
Maybe it's simpler than that? Looking into the GCC info pages, I found
this:
Starting with GCC version 4.6, the default setting (when not
optimizing for size) for 32-bit GNU/Linux x86 and 32-bit Darwin x86
targets has been changed to '-fomit-frame-pointer'. The default
can be reverted to '-fno-omit-frame-pointer' by configuring GCC
with the '--enable-frame-pointer' configure option.
Enabled at levels '-O', '-O2', '-O3', '-Os'.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
So it seems adding -fomit-frame-pointer file by file in Makefile.in
(when building with -O2) is moot and only has an effect when building
unoptimized, otherwise all files are built with -fomit-frame-pointer
anyway.
So, what if we drop all the -fomit-frame-pointer from Makefile.in and
add an
exceptions_CFLAGS:=-fno-omit-frame-pointer
Does that help?
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
Red Hat
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