Analyzing a SEG FAULT that gdb doesn't help with

Michael Enright
Thu Jul 30 17:46:00 GMT 2015

On Thu, Jul 30, 2015 at 7:39 AM, Jon TURNEY  wrote:
> You need to install the 'cygwin-debuginfo' package for debug symbols for
> cygwin1.dll

I missed this in my searches. I see now that I should have used the
"debug" category.

> You also need to point addr2line at those detached debug symbols, as (unlike
> gdb) it doesn't follow .gnu_debuglink pointers.
> (I'm assuming you've typoed 6155d363 here and it should be 0x6115D363 as the
> strace output says)

I've been having trouble getting that number right

> # addr2line -e /usr/lib/debug/usr/bin/cygwin1.dbg 0x6115D363
> /usr/src/debug/cygwin-2.1.0-1/newlib/libc/machine/i386/strlen.S:64

Another problem is that there's only one stack frame in the stack
dump, so knowing that it's a strlen just means I have to crank out
some grep commands and hopefully one of them is vulnerable to a
special case that now happens all the time.

> Are you sure the crashing process is the direct
> inferior of gdb, and not some wrapper process which runs it? (uninstalled
> libtool generated binaries do this, for e.g.)

The crashing executable is just a client of SpiderMonkey (via
libmozjs185) with several extensions to JavaScript in order to emulate
some of the Windows cscript utility and to emulate another environment
that happens to be a massive annoyance to run scripts in. The
executable is built using a textbook Makefile.

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