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Subject: Re: Cygwin debugger crashes every time on following a unique_ptr
To: The Cygwin Mailing List <cygwin AT cygwin DOT com>,
        Raj Kumar <gaurav AT iastate DOT edu>
References: <CAECqvgfWPBo0VmYk=EG14vQkK-L7f4zGZ==pv-jSMt31vhavZw AT mail DOT gmail DOT com> <4ffe9ce5-8504-f009-2b19-098bdc9b1aef AT maxrnd DOT com>
From: Jon Turney <jon DOT turney AT dronecode DOT org DOT uk>
Message-ID: <7a439630-5450-b41e-1f03-c93cfd356b67@dronecode.org.uk>
Date: Sun, 26 May 2019 17:40:10 +0100
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On 25/05/2019 22:31, Mark Geisert wrote:
> Raj Kumar wrote:
> [...]
>> Adding a watch is equivalent to when in the gdb window I try and do
>> this: myCar.get()->currentPassengers. This crashes the GDB every time.
>> So the issue occurs when I try to follow the object pointed to by a
>> unique_ptr and try to get its attributes/variables.
> 
> I can confirm this issue.  The fault is reported by Cygwin's memcpy().  
> I'm having a heck of a time trying to get a gdb backtrace to show what 
> in gdb itself is likely calling memcpy() with a bad arg.

When debugging gdb with itself here, you'll need to use 'set 
cygwin-exceptions on' to allow it to stop on exceptions inside the 
cygwin DLL.

See https://cygwin.com/faq.html#faq.programming.debugging-cygwin

(This would be a lot more usable if gdb ignored exceptions inside the 
specific functions where it makes sense to do that (e.g. 
verifyable_object_isvalid, etc.), rather than anywhere in the cygwin 
DLL, if someone wants to fix that...)

> To reproduce with OP's supplied source files in an otherwise clean 
> directory:
> g++ -g -o raj *.cpp
> gdb raj
> [...]
> (gdb) b main
> (gdb) run
> (gdb) n
> (gdb) n
> 
> At this point you'll be on line 14.  Issue the OP's triggering command:
> (gdb) p myCar.get()->currentPassengers
> Segmentation fault (core dumped)

Thanks for the reproduction instructions.

This seems to be the issue discussed in [1], fixed by [2].

This fix is contained in the 8.2.1-1 Cygwin test release of gdb.

[1] https://sourceware.org/ml/gdb-patches/2018-06/msg00584.html
[2] 
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commitdiff;h=de52b9607d2623f18b7a7dbee3e1123d8d63f5da

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