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Message-ID: <20181107233142.GV5150@brightrain.aerifal.cx>
Date: Wed, 7 Nov 2018 18:31:42 -0500
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: Problems with pthreads from a shared object?
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(>hread, 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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