Re: [PATCH] Stacktrace in ARM32 architecture has jumped the first 2 layers, which may ignore the display of save_stack_trace_tsk.

[Russell King - ARM Linux admin <linux@armlinux.org.uk>]

On Thu, May 30, 2019 at 11:06:39PM +0800, l00383200 wrote:
> Without optimization, both save_stack_trace_tsk and __save_stack_trace
> will have stacktrace information in ARM32.
> 
> In this situation, "data.skip += 2" operation will skip the first two layers,
> which may make the stacktrace strange and different from other architectures.
> 
> A simple example is as follows:
> In ARM32 architecture:
> [<ffffff80083cb3f8>] proc_pid_stack+0xac/0x12c
> [<ffffff80083c7c70>] proc_single_show+0x5c/0xa8
> [<ffffff800838aca8>] seq_read+0x130/0x420
> [<ffffff8008365c54>] __vfs_read+0x60/0x11c
> [<ffffff80083665dc>] vfs_read+0x8c/0x140
> [<ffffff800836717c>] SyS_read+0x6c/0xcc
> [<ffffff8008202cb8>] __sys_trace_return+0x0/0x4
> [<ffffffffffffffff>] 0xffffffffffffffff
> 
> In some other architectures(ARM64):
> [<ffffff8008209be0>] save_stack_trace_tsk+0x0/0xf0
> [<ffffff80083cb3f8>] proc_pid_stack+0xac/0x12c
> [<ffffff80083c7c70>] proc_single_show+0x5c/0xa8
> [<ffffff800838aca8>] seq_read+0x130/0x420
> [<ffffff8008365c54>] __vfs_read+0x60/0x11c
> [<ffffff80083665dc>] vfs_read+0x8c/0x140
> [<ffffff800836717c>] SyS_read+0x6c/0xcc
> [<ffffff8008202cb8>] __sys_trace_return+0x0/0x4
> [<ffffffffffffffff>] 0xffffffffffffffff
> 
> Therefore, we'd better just jump only one layer to ensure accuracy and consistency.

Why do we want to log the function we called to save the stack trace
_in_ the stack trace?  What useful purpose does it serve?

I've always taken the attitude that if we want a stack trace from a
certain point in the function, then that's the point that the stack
trace should start.  It's entirely sensible.

> 
> Signed-off-by: liucheng <liucheng32@huawei.com>
> ---
>  arch/arm/kernel/stacktrace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/kernel/stacktrace.c b/arch/arm/kernel/stacktrace.c
> index 71778bb..bb3da38 100644
> --- a/arch/arm/kernel/stacktrace.c
> +++ b/arch/arm/kernel/stacktrace.c
> @@ -125,7 +125,7 @@ static noinline void __save_stack_trace(struct task_struct *tsk,
>  #endif
>  	} else {
>  		/* We don't want this function nor the caller */
> -		data.skip += 2;
> +		data.skip += 1;
>  		frame.fp = (unsigned long)__builtin_frame_address(0);
>  		frame.sp = current_stack_pointer;
>  		frame.lr = (unsigned long)__builtin_return_address(0);
> -- 
> 1.8.5.6
> 
> 

-- 
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