(Sent to cygwin-developers by mistake).

When debugging a segfault in the Dillo browser[1] with the DNS threaded resolver and OpenSSL 3.0.13 I managed to isolate a reproducer.

[1]: https://github.com/dillo-browser/dillo/issues/172

It seems to be caused when both the SSL_library_init() is present and the PTHREAD_CREATE_DETACHED flag is set.

Steps to reproduce:

$ cat p.c
#include <pthread.h>
#include <unistd.h>
#include <stdio.h>

#include <openssl/ssl.h>

#define N 4

static void *foo(void *data)
        printf("hello th %d\n", (int) data);
        return NULL;

int main()
        pthread_t th[N];
        pthread_attr_t attr;
        pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);

        for (int i = 0; i < N; i++)
                pthread_create(&th[i], &attr, foo, (void *) i);


$ gcc p.c -lssl -pthread -o p

$ gdb ./p
GNU gdb (GDB) (Cygwin 13.2-1) 13.2
Copyright (C) 2023 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-pc-cygwin".
Type "show configuration" for configuration details.
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Reading symbols from ./p...
(gdb) r
Starting program: /home/PC/dillo/build-openssl/p
[New Thread 7332.0x1f2c]
[New Thread 7332.0x99c]
[New Thread 7332.0x27d4]
[New Thread 7332.0x35e0]
[New Thread 7332.0x21dc]
[New Thread 7332.0x3170]
[New Thread 7332.0x1ea4]
[New Thread 7332.0x3180]
hello th 0
hello th 1
hello th 2
[Thread 7332.0x3170 exited with code 0]
hello th 3

Thread 6 "p" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 7332.0x21dc]
0x0000000000000000 in ?? ()


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