Make Linux signal handler more robust.

Make Linux signal handler more robust.

Breakpad can be used on processes where a mistaken
library saves then restores one of our signal handlers
with 'signal' instead of 'sigaction'.

This loses the SA_SIGINFO flag associated with the 
Breakpad handler, and in some cases (e.g. Android/ARM
kernels), the values of the 'info' and 'uc' parameters
that ExceptionHandler::SignalHandler() receives will
be completely bogus, leading to a crash when the function
is executed (and of course, no minidump generation).

To work-around this, have SignalHandler() check the state
of the flag. If it is incorrectly unset, re-register with
'sigaction' and the correct flag, then return. The signal
will be re-thrown, and this time the function will be
called with the correct values.
Committed: https://code.google.com/p/google-breakpad/source/detail?r=1067

[digit]

Patch originally from cjhopman for Android, I'm just upstreaming our patch in a
tiny cleaner way.

[Mark Mentovai]

LGTM

http://breakpad.appspot.com/481002/diff/1/src/client/linux/handler/exception_...
File src/client/linux/handler/exception_handler.cc (right):

http://breakpad.appspot.com/481002/diff/1/src/client/linux/handler/exception_...
src/client/linux/handler/exception_handler.cc:260: if
(sigaction(kExceptionSignals[i], &sa, NULL) == -1)
I don’t see any reason to make this change. The {} was clearer, and the comment
read just fine before you changed it to start a sentence with “so.”

http://breakpad.appspot.com/481002/diff/1/src/client/linux/handler/exception_...
src/client/linux/handler/exception_handler.cc:304: // This forces the signal to
be throwned again, but this time the kernel
throwned -> thrown

[cjhopman]

lgtm

http://breakpad.appspot.com/481002/diff/1/src/client/linux/handler/exception_...
File src/client/linux/handler/exception_handler.cc (right):

http://breakpad.appspot.com/481002/diff/1/src/client/linux/handler/exception_...
src/client/linux/handler/exception_handler.cc:316: if (sigaction(sig,
&cur_handler, NULL) < 0) {
Nit: For consistency with the rest of the file, maybe change this to "== -1".

http://breakpad.appspot.com/481002/diff/1/src/client/linux/handler/exception_...
File src/client/linux/handler/exception_handler_unittest.cc (right):

http://breakpad.appspot.com/481002/diff/1/src/client/linux/handler/exception_...
src/client/linux/handler/exception_handler_unittest.cc:320: // Check that
Finish this comment.

http://breakpad.appspot.com/481002/diff/1/src/client/linux/handler/exception_...
src/client/linux/handler/exception_handler_unittest.cc:325: // Install the
RaiseSIGKILL handler for SIGSEGV
Nit: full stop

[digit]

http://breakpad.appspot.com/481002/diff/1/src/client/linux/handler/exception_...
File src/client/linux/handler/exception_handler.cc (right):

http://breakpad.appspot.com/481002/diff/1/src/client/linux/handler/exception_...
src/client/linux/handler/exception_handler.cc:260: if
(sigaction(kExceptionSignals[i], &sa, NULL) == -1)
Sorry, that wasn't intentional, my git and svn states got mixed up a bit.

http://breakpad.appspot.com/481002/diff/1/src/client/linux/handler/exception_...
src/client/linux/handler/exception_handler.cc:304: // This forces the signal to
be throwned again, but this time the kernel
On 2012/10/09 15:56:09, Mark Mentovai wrote:
> throwned -> thrown
Done.

http://breakpad.appspot.com/481002/diff/1/src/client/linux/handler/exception_...
src/client/linux/handler/exception_handler.cc:316: if (sigaction(sig,
&cur_handler, NULL) < 0) {
On 2012/10/09 16:12:02, cjhopman wrote:
> Nit: For consistency with the rest of the file, maybe change this to "== -1".
Sure, done.

http://breakpad.appspot.com/481002/diff/1/src/client/linux/handler/exception_...
File src/client/linux/handler/exception_handler_unittest.cc (right):

http://breakpad.appspot.com/481002/diff/1/src/client/linux/handler/exception_...
src/client/linux/handler/exception_handler_unittest.cc:320: // Check that
On 2012/10/09 16:12:02, cjhopman wrote:
> Finish this comment.
Done.

http://breakpad.appspot.com/481002/diff/1/src/client/linux/handler/exception_...
src/client/linux/handler/exception_handler_unittest.cc:325: // Install the
RaiseSIGKILL handler for SIGSEGV
On 2012/10/09 16:12:02, cjhopman wrote:
> Nit: full stop
Done.