re: toolchain/53918: X crashes on pinebook and stack unwinding broken

[matthew green <mrg%eterna.com.au@localhost>]

The following reply was made to PR toolchain/53918; it has been noted by GNATS.

From: matthew green <mrg%eterna.com.au@localhost>
To: toolchain-manager%netbsd.org@localhost, gnats-admin%netbsd.org@localhost,
    netbsd-bugs%netbsd.org@localhost, gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: re: toolchain/53918: X crashes on pinebook and stack unwinding broken
Date: Tue, 29 Jan 2019 11:32:31 +1100

 matthew green writes:
 > i hacked the xorg_backtrace() function into a simple test case that
 > also hangs on arm64 for me.
 > 
 
 this "fixes" the hang for me by avoiding an infinite loop in
 the libexecinfo unwind tracer() function, but it still shows
 that there is a bug in the handling (i had to fix a bug in the
 test program to call _exit(1) for this to work properly):
 
 soft-irony ~> ./a.out
 
 Backtrace:
 bt size = 2
 0: ./a.out (0x200100000+0xb18) [0x200100b18]
 1: ./a.out (0x200100000+0xcc4) [0x200100cc4]
 
 signo: 11
 
 Backtrace:
 bt size = 63
 0: ./a.out (0x200100000+0xb18) [0x200100b18]
 1: ./a.out (0x200100000+0xcb0) [0x200100cb0]
 2: /usr/lib/libc.so.12 (__sigtramp_siginfo_2+0x0) [0xf68683d9d6d0]
 3: /usr/lib/libc.so.12 (__sigtramp_siginfo_2+0x0) [0xf68683d9d6d0]
 4: /usr/lib/libc.so.12 (__sigtramp_siginfo_2+0x0) [0xf68683d9d6d0]
 [ ... ]
 62: /usr/lib/libc.so.12 (__sigtramp_siginfo_2+0x0) [0xf68683d9d6d0]
 
 soft-irony ~> 
 
 on amd64, this ends at frame#2 -- the libc trampoline.  on arm64
 it is recursing to itself.
 
 
 .mrg.
 
 
 Index: unwind.c
 ===================================================================
 RCS file: /cvsroot/src/lib/libexecinfo/unwind.c,v
 retrieving revision 1.2
 diff -p -u -r1.2 unwind.c
 --- unwind.c	24 Mar 2014 21:26:01 -0000	1.2
 +++ unwind.c	29 Jan 2019 00:29:30 -0000
 @@ -52,6 +52,8 @@ tracer(struct _Unwind_Context *ctx, void
  	}
  	if (t->n < t->len)
  		t->arr[t->n++] = (void *)_Unwind_GetIP(ctx);
 +	else
 +		return 1; // other code better, but will do for now
  	return 0;
  }