linux-kernel - Re: [PATCH v3 1/7] arm64: ftrace: adjust callsite addresses examined by stack tracer

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Message-ID: <20151013113750.0fdecd33@gandalf.local.home>
Date:	Tue, 13 Oct 2015 11:37:50 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc:	catalin.marinas@....com, will.deacon@....com,
	jungseoklee85@...il.com, olof@...om.net, broonie@...nel.org,
	david.griego@...aro.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/7] arm64: ftrace: adjust callsite addresses
 examined by stack tracer

On Thu,  8 Oct 2015 19:01:38 +0900
AKASHI Takahiro <takahiro.akashi@...aro.org> wrote:

>  extern int stack_tracer_enabled;
>  int
>  stack_trace_sysctl(struct ctl_table *table, int write,
> diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
> index b746399..30521ea 100644
> --- a/kernel/trace/trace_stack.c
> +++ b/kernel/trace/trace_stack.c
> @@ -105,7 +105,7 @@ check_stack(unsigned long ip, unsigned long *stack)
>  
>  	/* Skip over the overhead of the stack tracer itself */
>  	for (i = 0; i < max_stack_trace.nr_entries; i++) {
> -		if (stack_dump_trace[i] == ip)
> +		if ((stack_dump_trace[i] + FTRACE_STACK_FRAME_OFFSET) == ip)
>  			break;
>  	}
>  
> @@ -133,7 +133,8 @@ check_stack(unsigned long ip, unsigned long *stack)
>  		for (; p < top && i < max_stack_trace.nr_entries; p++) {
>  			if (stack_dump_trace[i] == ULONG_MAX)
>  				break;
> -			if (*p == stack_dump_trace[i]) {
> +			if (*p == (stack_dump_trace[i]
> +					+ FTRACE_STACK_FRAME_OFFSET)) {

I'm fine with the patch, but this is one of those cases that I think
the 80 column max limit produces uglier code than just going a little
over.

Or, we can add a helper variable in both locations:

	addr = stack_dump_trace[i] + FTRACE_STACK_FRAME_OFFSET;
	if (*p == addr) {

gcc should be smart enough to optimize out the addr variable.

-- Steve

>  				stack_dump_trace[x] = stack_dump_trace[i++];
>  				this_size = stack_dump_index[x++] =
>  					(top - p) * sizeof(unsigned long);

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