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Re: Cygwin debugger crashes every time on following a unique_ptr




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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