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Re: [PATCH] tile: fix DWARF bug in clone() for created thread
- From: Chris Metcalf <cmetcalf at tilera dot com>
- To: <libc-ports at sourceware dot org>, "David S. Miller" <davem at davemloft dot net>
- Date: Fri, 21 Dec 2012 15:14:05 -0500
- Subject: Re: [PATCH] tile: fix DWARF bug in clone() for created thread
- References: <201212141551.qBEFpsJe000377@farm-0002.internal.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