linux-kernel - Re: [PATCH] tracing/trace_stack: Fix stack trace on ppc64

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Message-ID: <1283218310.1377.50.camel@gandalf.stny.rr.com>
Date:	Mon, 30 Aug 2010 21:31:50 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Anton Blanchard <anton@...ba.org>
Cc:	fweisbec@...il.com, mingo@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing/trace_stack: Fix stack trace on ppc64

On Wed, 2010-08-25 at 11:32 +1000, Anton Blanchard wrote:
> save_stack_trace() stores the instruction pointer, not the function
> descriptor. On ppc64 the trace stack code currently dereferences the
> instruction pointer and shows 8 bytes of instructions in our backtraces:
> 
> # cat /sys/kernel/debug/tracing/stack_trace
>         Depth    Size   Location    (26 entries)
>         -----    ----   --------
>   0)     5424     112   0x6000000048000004
>   1)     5312     160   0x60000000ebad01b0
>   2)     5152     160   0x2c23000041c20030
>   3)     4992     240   0x600000007c781b79
>   4)     4752     160   0xe84100284800000c
>   5)     4592     192   0x600000002fa30000
>   6)     4400     256   0x7f1800347b7407e0
>   7)     4144     208   0xe89f0108f87f0070
>   8)     3936     272   0xe84100282fa30000
> 
> Since we aren't dealing with function descriptors, use %pS instead of %pF
> to fix it:
> 
> # cat /sys/kernel/debug/tracing/stack_trace
>         Depth    Size   Location    (26 entries)
>         -----    ----   --------
>   0)     5424     112   ftrace_call+0x4/0x8
>   1)     5312     160   .current_io_context+0x28/0x74
>   2)     5152     160   .get_io_context+0x48/0xa0
>   3)     4992     240   .cfq_set_request+0x94/0x4c4
>   4)     4752     160   .elv_set_request+0x60/0x84
>   5)     4592     192   .get_request+0x2d4/0x468
>   6)     4400     256   .get_request_wait+0x7c/0x258
>   7)     4144     208   .__make_request+0x49c/0x610
>   8)     3936     272   .generic_make_request+0x390/0x434
> 
> Signed-off-by: Anton Blanchard <anton@...ba.org>

Thanks, I'll test this to make sure it doesn't break x86, and then push
it into a stable/-rc patch queue.

-- Steve

> ---
> 
> Index: powerpc.git/kernel/trace/trace_stack.c
> ===================================================================
> --- powerpc.git.orig/kernel/trace/trace_stack.c	2010-08-25 11:03:52.337982567 +1000
> +++ powerpc.git/kernel/trace/trace_stack.c	2010-08-25 11:03:55.018371055 +1000
> @@ -249,7 +249,7 @@ static int trace_lookup_stack(struct seq
>  {
>  	unsigned long addr = stack_dump_trace[i];
>  
> -	return seq_printf(m, "%pF\n", (void *)addr);
> +	return seq_printf(m, "%pS\n", (void *)addr);
>  }
>  
>  static void print_disabled(struct seq_file *m)


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