Re: Problems with pthreads from a shared object?

[Barry Flartus <barry.flartus@gmail.com>]

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Nope! Linux ubuntu-x64 4.4.0-116-generic -  this is just the kernel from a
default Ubuntu 16.04 install.

On Wed, Nov 7, 2018 at 6:31 PM Rich Felker <dalias@libc.org> wrote:

> On Wed, Nov 07, 2018 at 06:00:14PM -0500, Barry Flartus wrote:
> > 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!
>
> Are you running on an ancient kernel or a kernel built with a lot of
> default functionality configured out? These should be the only
> conditions under which pthread_create can return ENOSYS.
>
> Rich
>

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