Re: [PATCH] perf uprobe: Skip prologue if program compiled without optimization

[Ravi Bangoria]

Thanks Masami,

On Tuesday 02 August 2016 08:22 PM, Masami Hiramatsu wrote:
> On Mon,  1 Aug 2016 14:19:28 +0530
> Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxxxxxxx> wrote:
>
> > Function prologue prepares stack and registers before executing function
> > logic. When target program is compiled without optimization, function
> > parameter information is only valid after prologue. When we probe entrypc
> > of the function, and try to record function parameter, it contains
> > garbage value.
[SNIP]
> > +
> > +	/* Only FUNC and FUNC@SRC are eligible. */
> > +	if (!pp->function || pp->line || pp->retprobe || pp->lazy_line ||
> > +	    pp->offset || pp->abs_address)
> > +		return;
> > +
> > +	/* Not interested in func parameter? */
> > +	if (!pf->pev->nargs)
> > +		return;
> Hmm, this is not enough, since perf-probe accepts registers and stacks.
> At least you should check if all argument are !is_c_varname(), !PROBE_ARG_VARS and
> !PROBE_ARG_PARAMS here, instead of checking nargs.
>
> > +
> > +	pr_info("Target program is compiled without optimization. Skipping prologue.\n"
> > +		"Use %s:1 or absolute address 0x%lx to force probe on entry point.\n\n",
> Hmm, is <Function>:1 always available? I think we should just recommend to use only
> the address.
> (moreover, pf->addr may not the absolute address in uprobe event, we'd better say
>   "the address 0x%x")

Nice catch. :)

Sent v2. Please review it.

-Ravi