Re: [PATCH 1/4] tracing/histogram: Don't use strlen to find length of stacktrace variables

[Steven Rostedt]

On Tue, 14 Feb 2023 00:24:18 +0900
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> wrote:

> > -				e = stack_trace_save((void *)str,
> > +				e = stack_trace_save((void *)stack_start,
> >  						     HIST_STACKTRACE_DEPTH,
> >  						     HIST_STACKTRACE_SKIP);  
> 
> BTW, the size of "str" is enough to store HIST_STACKTRACE_DEPTH?
> In string case, 
> 
> size = min(val->size, STR_VAR_LEN_MAX);
> 
> will limit the max size.

Well, we have:

#define HIST_STACKTRACE_DEPTH  16

And 16 * 8 = 128

#define STR_VAR_LEN_MAX              MAX_FILTER_STR_VAL
#define MAX_FILTER_STR_VAL 256U

So 128 < 256, with plenty of room. I wouldn't do this runtime, but we
should add here:

	BUILD_BUG_ON((HIST_STACKTRACE_DEPTH + 1) * sizeof(long) >= STR_VAR_LEN_MAX);

-- Steve