program exit code, "at exit" handler and explicit close of shared objects

[Ken Brown]

On 10/29/2019 10:53 AM, Ken Brown wrote:
> On 10/26/2019 11:07 AM, Roumen Petrov wrote:
>>
>> After additional tests (research) I was able to isolate issues to simple test
>> case. Please find attached "test-dlclose.c" and "Makefile".
>> First test is as is:
>>
>> $ make
>> cc -g -Wall -Wextra    test-dlclose.c   -o test-dlclose
>> ./test-dlclose
>> exit with code 33
>> make: [Makefile:4: all] Error 33 (ignored)
>>
>> For next test change test-dlclose.c to define DLCLOSE_ATEXIT ( s/#if 0/#if 1/ ):
>> $ make
>> cc -g -Wall -Wextra    test-dlclose.c   -o test-dlclose
>> ./test-dlclose
>> exit with code 33
> 
> I ran this second version of test-dlclose (with DLCLOSE_ATEXIT defined) under
> strace and got the following:
> 
> $ strace -o trace.out ./test-dlclose.exe
> exit with code 33
> Segmentation fault
> 
> The strace output ends with
> 
>      30   30143 [main] test-dlclose 847 write: 18 = write(1, 0x600061E20, 18)
> --- Process 33456 (pid: 847) unloaded DLL at 00000003e7930000
> --- Process 33456 (pid: 847), exception c0000005 at 00000003e7931080
> --- Process 33456 (pid: 847) thread 26088 exited with status 0xc0000005
> --- Process 33456 (pid: 847) thread 33544 exited with status 0xc0000005
> --- Process 33456 (pid: 847) thread 36020 exited with status 0xc0000005
> --- Process 33456 exited with status 0xc0000005
> 
> The address 00000003e7930000 seems to be in /usr/bin/cygz.dll, which is the DLL

Sorry, I meant to say 00000003e7931080; 00000003e7930000 is the start of cygz.dll.

> that got unloaded.  After installing zlib-debuginfo, I ran addr2line to see
> where the crash occurred, and this too crashed:
> 
> $ addr2line -C -f -i -p -e /usr/bin/cygz.dll 0x3e7931080
> Segmentation fault (core dumped)
> 
> That's as far as I've gotten.
> 
> Ken
> 
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