Segfault in _Unwind_* code called from pthread_exit

[Tijl Coosemans]

Hi,

The following program segfaults for me on amd64 when linked like this:

cc -o test test.c -lpthread -L/usr/local/lib/gcc5 -lgcc_s -rpath /usr/local/lib/gcc5

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

void *
thr( void *arg ) {
	return( NULL );
}

int
main( void ) {
	pthread_t thread;

	for( int i = 1; i < 20; i++ ) {
		fprintf( stderr, "%d\n", i );
		pthread_create( &thread, NULL, thr, NULL );
		pthread_join( thread, NULL );
	}
	return( 0 );
}
--------------------------------

The backtrace looks like this:

Thread 7 received signal SIGSEGV, Segmentation fault.
[Switching to LWP 100511 of process 1886]
uw_frame_state_for (context=context at entry=0x7fffdfffddc0, 
    fs=fs at entry=0x7fffdfffdb10)
    at /usr/ports/lang/gcc5/work/gcc-5.4.0/libgcc/unwind-dw2.c:1249
1249	/usr/ports/lang/gcc5/work/gcc-5.4.0/libgcc/unwind-dw2.c: No such file or directory.
(gdb) bt
#0  uw_frame_state_for (context=context at entry=0x7fffdfffddc0, 
    fs=fs at entry=0x7fffdfffdb10)
    at /usr/ports/lang/gcc5/work/gcc-5.4.0/libgcc/unwind-dw2.c:1249
#1  0x0000000800a66ecb in _Unwind_ForcedUnwind_Phase2 (
    exc=exc at entry=0x800658730, context=context at entry=0x7fffdfffddc0)
    at /usr/ports/lang/gcc5/work/gcc-5.4.0/libgcc/unwind.inc:155
#2  0x0000000800a67200 in _Unwind_ForcedUnwind (exc=0x800658730, 
    stop=0x8008428b0 <thread_unwind_stop>, stop_argument=0x0)
    at /usr/ports/lang/gcc5/work/gcc-5.4.0/libgcc/unwind.inc:207
#3  0x0000000800842224 in _Unwind_ForcedUnwind (ex=0x800658730, 
    stop_func=0x8008428b0 <thread_unwind_stop>, stop_arg=0x0)
    at /usr/src/lib/libthr/thread/thr_exit.c:106
#4  0x000000080084269f in thread_unwind ()
    at /usr/src/lib/libthr/thread/thr_exit.c:172
#5  0x00000008008424d6 in _pthread_exit_mask (status=0x0, mask=0x0)
    at /usr/src/lib/libthr/thread/thr_exit.c:254
#6  0x0000000800842359 in _pthread_exit (status=0x0)
    at /usr/src/lib/libthr/thread/thr_exit.c:206
#7  0x000000080082ccb1 in thread_start (curthread=0x800658500)
    at /usr/src/lib/libthr/thread/thr_create.c:289
#8  0x00007fffdfdfe000 in ?? ()
Backtrace stopped: Cannot access memory at address 0x7fffdfffe000


It happens with gcc6 as well, but not with base libgcc_s.
Can anyone reproduce this?  Have there been any changes to stack
unwinding recently (last few months)?