Hello,

I am encountering some issues that I believe are musl related when trying to

use pthreads from a shared object. Below is a minimal example (2 files) of the problem.

==================== test.c ====================

// Compile with

// musl-gcc -Wall -lpthread -shared -fPIC test.c -o test.so

#include <pthread.h>

#include <stdio.h>

static void *launch(void *arg);

int start_thread(void);

void entry_point(void) __attribute__((constructor));

static pthread_t gthread;

static void *launch(void *arg)

{

    for (int i = 0; i < 4; i++){

        printf("[%d] Hello from the thread\n", i);

    }

    return NULL;

}

int start_thread(void)

{

    printf("Starting the thread\n");

    return pthread_create(&gthread, NULL, launch, NULL);

}

void entry_point(void){

    puts("Starting Execution");

    int res = start_thread();

    printf("start_thread returned %d\n", res);

    if (res == 0){

        pthread_join(gthread, NULL);

    } else {

        printf("pthread_create() returned an error. Aborting.\n");

    }

}

==================== launch.c ====================

// Compile with:

// gcc launch.c -ldl -o launch

#include <dlfcn.h>

#include <stdio.h>

#include <stdlib.h>

int main(){

    void *handle;

    puts("\nLaunching test...");

    handle = dlopen("./test.so", RTLD_NOW);

    if (!handle) {

        fprintf(stderr, "%s\n", dlerror());

        exit(EXIT_FAILURE);

    }

    dlerror();

    return EXIT_SUCCESS;

}

When the above examples are compiled with gcc, everything works correctly and 

produces the following output:

Launching test...

Starting Execution

Starting the threadstart_thread returned 0

[0] Hello from the thread

[1] Hello from the thread

[2] Hello from the thread

[3] Hello from the thread

When I switch to musl pthread_create() returns the integer '38', which is an

undocumented return value. I assume this corresponds with ENOSYS from errno.h

but I can't seem to figure out why this is happening.

Output:

Launching test...

Starting Execution

Starting the thread

start_thread returned 38

pthread_create() returned an error. Aborting.

Is this even supported by musl? If so, where have I gone wrong?

Thanks in advance!