On 8/16/2020 9:52 AM, Takashi Yano via Cygwin wrote:
On Sun, 16 Aug 2020 09:21:24 -0400
Ken Brown via Cygwin <cygwin@cygwin.com> wrote:
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@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.
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
Thanks for the information. But I still wonder why 32-bit and 64-bit
cygwin behave differently.
I'm no C++ expert, but my understanding after a brief internet search is that an
uncaught exception is supposed to cause std::terminate to be called. So I
installed gcc-debuginfo and ran the OP's test case under gdb with a breakpoint
at 'terminate'. On 32-bit Cygwin I got the expected behavior:
Thread 1 "exception_test" hit Breakpoint 1, std::terminate ()
at /usr/src/debug/gcc-9.3.0-2/libstdc++-v3/libsupc++/eh_terminate.cc:96
96 __atomic_load (&__terminate_handler, &func, __ATOMIC_ACQUIRE);
(gdb) bt
#0 std::terminate ()
at /usr/src/debug/gcc-9.3.0-2/libstdc++-v3/libsupc++/eh_terminate.cc:96
#1 0x57c45909 in __cxxabiv1::__cxa_throw (obj=obj@entry=0x800396e8,
tinfo=tinfo@entry=0x57c646a8 <typeinfo for std::logic_error>,
dest=0x57be6c60 <std::logic_error::~logic_error()>)
at /usr/src/debug/gcc-9.3.0-2/libstdc++-v3/libsupc++/eh_throw.cc:95
#2 0x57c49223 in std::__throw_logic_error (
__s=__s@entry=0x57c60160 <cplus_demangle_builtin_types+10272>
"basic_string::
_S_construct null not valid")
at /usr/src/debug/gcc-9.3.0-2/libstdc++-v3/src/c++11/functexcept.cc:66
[...]
On 64-bit Cygwin, however, I got the behavior reported by the OP:
gdb: unknown target exception 0x20474343 at 0x7ff8cccca719
Thread 1 "exception_test" received signal ?, Unknown signal.
0x00007ff8cccca719 in RaiseException () from /c/WINDOWS/System32/KERNELBASE.dll
(gdb) c
Continuing.
[Thread 4508.0x3e20 exited with code 541541187]
[Thread 4508.0x5bc exited with code 541541187]
[Thread 4508.0x5ee8 exited with code 541541187]
[Thread 4508.0x1cd0 exited with code 541541187]
[Inferior 1 (process 4508) exited with code 04021641503]
Note that the breakpoint at 'terminate' is not reached. I tried putting a
breakpoint at __cxa_throw and stepping through from there, but I don't really
understand what's going on. Someone who knows the innards of exception handling
will have to look at this.
Ken
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