unhandled C++ exceptions not propagating

[David McFarland]

Takashi Yano <takashi.yano@nifty.ne.jp> writes:

> On Sat, 15 Aug 2020 20:38:01 -0300
> David McFarland via Cygwin <cygwin@cygwin.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.

Yeah, it seems to be.  Thanks for tracking that down.

I tried using ProcessMonitor, and when I run the test program from a
shell (where it appears to return 0) I get:

a.exe	7096	Process Exit		SUCCESS	Exit Status: 541541187, User Time: 0.0000000 seconds, Kernel Time: 0.0000000 seconds, Private Bytes: 4,661,248, Peak Private Bytes: 4,661,248, Working Set: 4,255,744, Peak Working Set: 4,259,840

So the win32 process does appear to be exiting non-zero.

Did you find out anything else when you investigated it? My next step
was going to be digging into why it behaves differently under strace.