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From: Roumen Petrov <bugtrack AT roumenpetrov DOT info>
Subject: program exit code, "at exit" handler and explicit close of shared objects
To: cygwin AT cygwin DOT com
Message-ID: <a24efbf6-872e-1e5b-017a-b14c59d84550@roumenpetrov.info>
Date: Sat, 26 Oct 2019 18:07:11 +0300
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Hello Cygwin developers,

This email is mainly for issue with exist code for a program.

It is inspired from openssl issue #10107 - "test_ssl_old freezes on 
cygwin". Actually after one or another work-around "unfreeze" test and 
this shows that one of subtests fail. This failure is main topic of this 
email.

More about failed test "testing connection with weak DH, expecting 
failure". So failure is expected and program code try to exit with 1. 
Unfortunately OS returns zero exit code.
Since version 1.1 OpenSSL uses "at exit handler" to clean-up allocated 
resources. Removing registered handler restores program exit code. So 
something in handler triggers issue.

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

As is visible make does not report error, i.e. program exit code is zero.

Is there a way to bypass issue?


For protocol:
$ uname -srvm -> CYGWIN_NT-10.0 3.0.7(0.338/5/3) 2019-04-30 18:08 x86_64

Regards,
Roumen Petrov

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#include <dlfcn.h>
#include <stdio.h>
#include <stdlib.h>

void *handle = NULL;

#if 0
# define DLCLOSE_ATEXIT	1
#endif

#ifdef DLCLOSE_ATEXIT
static void
dlclose_atexit(void) {
	if (dlclose(handle) != 0) {
		fprintf(stderr, "dlclose fail : %s\n", dlerror());
	}
}
#endif

int
main() {
	handle = dlopen("libz.so", RTLD_LAZY | RTLD_NOW);
	if (handle == NULL) {
		fprintf(stderr, "dlopen fail : %s\n", dlerror());
		return 1;
	}

#ifndef DLCLOSE_ATEXIT
	if (dlclose(handle) != 0) {
		fprintf(stderr, "dlclose fail : %s\n", dlerror());
		return 2;
	}
#else
    if (atexit(dlclose_atexit) != 0) {
		fprintf(stderr, "atexit fail\n");
		return 3;		
	}
#endif

	printf("exit with code 33\n");
	return 33;
}


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