Re: [PATCH] tile: fix DWARF bug in clone() for created thread

[Chris Metcalf <cmetcalf@tilera.com>]

On 12/14/2012 10:46 AM, Chris Metcalf wrote:
>   [David - this is pretty low risk (just adds one DWARF CFI directive),
>   but also fixes a pretty minor bug.  So your call as to whether I should
>   wait for 2.18 to commit.]

Ping?  I like the idea of fixing this in 2.17 just because customers tend to go "WTF?" when they see this in the debugger output.

> Previously, we would see a bad frame in the gdb backtrace output, e.g.:
>
>   (gdb) bt
>   #0  foo () at foo.c:5
>   #1  0x000000aaaab68ee8 in start_thread () from /lib/libpthread.so.0
>   #2  0x000000aaaad01c88 in clone () from /lib/libc.so.6
>   #3  0x0000000000000000 in ?? ()
>
> With this change the bogus frame #3 is gone and we have the
> same output as x86 does for the same program.
>
> 2012-12-14  Chris Metcalf  <cmetcalf@tilera.com>
>
> 	* sysdeps/unix/sysv/linux/tile/nptl/clone.S: Fix DWARF info.
>
> diff --git a/ports/sysdeps/unix/sysv/linux/tile/nptl/clone.S b/ports/sysdeps/unix/sysv/linux/tile/nptl/clone.S
> index de4fa13..27592cc 100644
> --- a/ports/sysdeps/unix/sysv/linux/tile/nptl/clone.S
> +++ b/ports/sysdeps/unix/sysv/linux/tile/nptl/clone.S
> @@ -160,6 +160,8 @@ ENTRY (__clone)
>     r32: the user function pointer  */
>  
>  .Lthread_start:
> +	cfi_def_cfa_offset (FRAME_SIZE)
> +	cfi_undefined (lr)
>  	/* Check and see if we need to reset the PID, which we do if
>  	   CLONE_THREAD isn't set, i.e. we're not staying in the thread group.
>  	   If CLONE_VM is set, we're doing some kind of thread-like clone,
> @@ -167,7 +169,6 @@ ENTRY (__clone)
>  	   in getpid().  Otherwise (if CLONE_VM isn't set), it's a
>  	   fork-like clone, and we go ahead and write the cached values
>  	   from the true system pid (retrieved via __NR_getpid syscall).  */
> -	cfi_def_cfa_offset (FRAME_SIZE)
>  #ifdef __tilegx__
>  	{
>  	 moveli r0, hw1_last(CLONE_VM)

-- 
Chris Metcalf, Tilera Corp.
http://www.tilera.com