pthread cleanup functions

Paul Floyd

2024-03-01 10:22:35 UTC

Hi

Can anyone explain what the pthread cleanup functions do?

I'm getting errors from Valgrind on arm64:

==8227== Invalid read of size 8
==8227== at 0x48FFE78: __pthread_cleanup_pop_imp (in /lib/libthr.so.3)
==8227== Address 0x1ffeffedf0 is on thread 2's stack
==8227== 328 bytes below stack pointer

I'm not doing a good job with the callstack, in gdb it's clearer and
looks OK:

(gdb) bt
#0 __thr_cleanup_pop_imp (execute=***@entry=1) at
/usr/src/lib/libthr/thread/thr_clean.c:78
#1 0x0000000004901aa4 in _pthread_exit_mask (status=<optimized out>,
mask=<optimized out>, ***@entry=0x1ffeffefa8)
at /usr/src/lib/libthr/thread/thr_exit.c:260
#2 0x0000000004901944 in _Tthr_exit (status=0x1) at
/usr/src/lib/libthr/thread/thr_exit.c:207
#3 0x0000000004901350 in thread_start (curthread=0x557c780) at
/usr/src/lib/libthr/thread/thr_create.c:290
#4 0x0000000004900ec0 in _pthread_create (thread=0x1ffffff930,
attr=<optimized out>, start_routine=<optimized out>, arg=<optimized out>)
at /usr/src/lib/libthr/thread/thr_create.c:185
#5 0x0000000000210840 in main () at pthread.c:22

That's on line 78 below. curthread->cleanup is not NULL but it points to
invalid memory.

71 void
72 __thr_cleanup_pop_imp(int execute)
73 {
74 struct pthread *curthread = _get_curthread();
75 struct pthread_cleanup *old;
76
77 if ((old = curthread->cleanup) != NULL) {
78 curthread->cleanup = old->prev;
79 if (execute)
80 old->routine(old->routine_arg);
81 if (old->onheap)
82 free(old);

83 }
84 }

This is just running a trivial example

#include <pthread.h>
#include <stdio.h>

void* func(void* arg)
{
int a;
fprintf(stderr, "in func arg passed is %p\n", arg);
fprintf(stderr, "in func arg my stack is around %p\n", &a);
return NULL;
}

int main(void)
{
int arg = 42;
pthread_t tid;
fprintf(stderr, "arg passed is %p\n", &arg);
pthread_create(&tid,
NULL,
func,
&arg);

pthread_join(tid, NULL);
}

A+
Paul

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