linux-kernel - Re: [RFC][PATCH -tip 7/9] tracing: kprobe-tracer plugin supports arguments

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Date:	Fri, 20 Mar 2009 13:49:14 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	systemtap-ml <systemtap@...rces.redhat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH -tip 7/9] tracing: kprobe-tracer plugin supports
	arguments

On Thu, Mar 19, 2009 at 05:10:40PM -0400, Masami Hiramatsu wrote:

> +#if defined(__i386__)
> +#define REGPARMS 3
> +static unsigned long fetch_argument(struct pt_regs *regs, void *data)
> +{
> +	unsigned long n = (unsigned long)data;
> +	if (n > REGPARMS) {
> +		/*
> +		 * The typical case: arg n is on the stack.
> +		 * stack[0] = return address
> +		 */
> +		return fetch_stack(regs, (void *)(n - REGPARMS));
> +	} else {
> +		switch (n) {
> +		case 1: return regs->ax;
> +		case 2: return regs->dx;
> +		case 3: return regs->cx;
> +		}
> +		return 0;
> +	}
> +}
> +#elif define(__x86_64__)

#elif defined(__x86_64__)

> +#define REGPARMS 6
> +static unsigned long fetch_argument(struct pt_regs *regs, void *data)
> +{
> +	unsigned long n = (unsigned long)data;
> +	if (n > REGPARMS) {
> +		/*
> +		 * The typical case: arg n is on the stack.
> +		 * stack[0] = return address
> +		 */
> +		return fetch_stack(regs, (void *)(n - REGPARMS));
> +	} else {
> +		switch (n) {
> +		case 1: return regs->di;
> +		case 2: return regs->si;
> +		case 3: return regs->dx;
> +		case 4: return regs->cx;
> +		case 5: return regs->r8;
> +		case 6: return regs->r9;
> +		}
> +		return 0;
> +	}
> +}
> +#else
> +static unsigned long fetch_argument(struct pt_regs *regs, void *data)
> +{
> +	return fetch_stack(regs, data);
> +}
> +#endif

As mentioned in another email, if we can generalize something similar to
syscall_get_arguments, this can be made to work for many !x86 archs.
AFAICS the calling conventions mandated by the ABI are followed at
syscall time, isn't it?

Ananth
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