[Bug debug/86257] Program compiled with fPIC crashes while stepping over thread-local variable GDB

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86257

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code, wrong-debug
             Target|                            |x86_64-*-*
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2018-06-21
            Version|4.4.7                       |8.1.1
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Testcase from stackoverflow

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

#define MAX_NUMBER_OF_THREADS 2

struct mystruct {
    int   x;
    int   y;
};

__thread struct mystruct obj;

void* threadMain(void *args) {
    obj.x = 1;
    obj.y = 2;

    printf("obj.x = %d\n", obj.x);
    printf("obj.y = %d\n", obj.y);

    return NULL;
}

int main(int argc, char *arg[]) {
    pthread_t tid[MAX_NUMBER_OF_THREADS];
    int i = 0;

    for(i = 0; i < MAX_NUMBER_OF_THREADS; i++) {
        pthread_create(&tid[i], NULL, threadMain, NULL);
    }

    for(i = 0; i < MAX_NUMBER_OF_THREADS; i++) {
        pthread_join(tid[i], NULL);
    }

    return 0;
}

and my reproduction with GCC 8:

> gcc-8 t.c -g -lpthread -fPIC
> gdb ./a.out 
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Reading symbols from ./a.out...done.
(gdb) b threadMain
Breakpoint 1 at 0x4006cf: file t.c, line 15.
(gdb) r
Starting program: /tmp/a.out 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
[New Thread 0x7ffff781d700 (LWP 12830)]
[New Thread 0x7ffff701c700 (LWP 12831)]
[Switching to Thread 0x7ffff781d700 (LWP 12830)]

Thread 2 "a.out" hit Breakpoint 1, threadMain (args=0x0) at t.c:15
15          obj.x = 1;
(gdb) p obj.x
$1 = 0
(gdb) n

Thread 2 "a.out" received signal SIGSEGV, Segmentation fault.
threadMain (args=0x0) at t.c:15
15          obj.x = 1;