linux-kernel - Re: [PATCH 05/19] x86/dumpstack: fix function graph tracing stack dump reliability issues

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Date:	Tue, 2 Aug 2016 22:59:36 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Brian Gerst <brgerst@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Byungchul Park <byungchul.park@....com>
Subject: Re: [PATCH 05/19] x86/dumpstack: fix function graph tracing stack
 dump reliability issues

On Tue, 2 Aug 2016 21:50:12 -0500
Josh Poimboeuf <jpoimboe@...hat.com> wrote:


> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 1e814ae..fc508a7 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -795,7 +795,9 @@ struct ftrace_ret_stack {
>  	unsigned long func;
>  	unsigned long long calltime;
>  	unsigned long long subtime;
> +#if defined(CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST) && !defined(CC_USING_FENTRY)

We need to make a new defined in ftrace.h:

#if defined(CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST) && !defined(CC_USING_FENTRY)
# define HAVE_FUNCTION_GRAPH_FP_TEST
#endif

And use that instead of this && complexity.

Or better yet, get rid of the CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST define
and only have HAVE_FUNCTION_GRAPH_FP_TEST defined in the asm/ftrace.h
in each arch. Then, x86 could just do;

#ifndef CC_USING_FENTRY
# define HAVE_FUNCTION_GRAPH_FP_TEST
#endif


-- Steve

>  	unsigned long fp;
> +#endif
>  };
>  
>  /*
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index 9caa9b2..86b2719 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -171,7 +171,9 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func, int *depth,
>  	current->ret_stack[index].func = func;
>  	current->ret_stack[index].calltime = calltime;
>  	current->ret_stack[index].subtime = 0;
> +#if defined(CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST) && !defined(CC_USING_FENTRY)
>  	current->ret_stack[index].fp = frame_pointer;
> +#endif
>  	*depth = current->curr_ret_stack;
>  
>  	return 0;