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Subject: Re: unhandled C++ exceptions not propagating
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From: Ken Brown via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Ken Brown <kbrown AT cornell DOT edu>
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On 8/15/2020 11:53 PM, Takashi Yano via Cygwin wrote:
> On Sat, 15 Aug 2020 20:38:01 -0300
> David McFarland via Cygwin <cygwin AT cygwin DOT com> wrote:
>>
>> I was just debugging a c++ app (b2 build system from boost), and noticed
>> that it would appear to exit unexpectedly without an error.  This turned
>> out to be when an unhandled C++ exception was thrown.
>>
>> On a fresh install of cygwin with gcc-g++, this program will throw an
>> exception from the std::string constructor:
>>
>> c++ -x c++ - <<END
>> #include <string>
>> int main() { std::string str(nullptr); return 0; }
>> END
>>
>> When it's executed from the shell it returns zero, but execution stops
>> at the exception.
>>
>> $ ./a; echo $?
>> 0
>>
>> When executed under gdb, the exception is caught, and the process exits
>> non-zero when continued:
>>
>> (gdb) r
>> Starting program: /home/corngood/a
>> [New Thread 4300.0x1390]
>> [New Thread 4300.0x1d24]
>> [New Thread 4300.0x1d48]
>> [New Thread 4300.0x80c]
>> gdb: unknown target exception 0x20474343 at 0x7ff8d2cfa799
>> Thread 1 "a" received signal ?, Unknown signal.
>> 0x00007ff8d2cfa799 in RaiseException () from /cygdrive/c/WINDOWS/System32/KERNELBASE.dll
>> (gdb) c
>> Continuing.
>> [Thread 4300.0x1d24 exited with code 541541187]
>> [Thread 4300.0x1870 exited with code 541541187]
>> [Thread 4300.0x1d48 exited with code 541541187]
>> [Thread 4300.0x1390 exited with code 541541187]
>> [Inferior 1 (process 4300) exited with code 04021641503]
>> (gdb)
>>
>> When executed under strace, it exits with an error as expected:
>>
>> $ strace -o /dev/null a; echo $?
>> 67
>>
>> That's as far as I've investigated so far.
> 
> Is this the same issue with
> https://cygwin.com/pipermail/cygwin/2019-October/242795.html ?
> 
> As far as I tested, this does not occur in 32-bit cygwin.

This doesn't seem to be a new issue.  I found the following report from 6 years 
ago, on Cygwin 1.7.30 with GCC 4.9.0:

 
https://stackoverflow.com/questions/24402412/program-executed-on-cygwin-does-not-report-a-thrown-exception

Ken
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