Re: [PATCH] LTT for 2.5.36 9/9: ARM trace support

[Russell King <rmk@arm.linux.org.uk>]

You should probably explicitly CC the architecture maintainers with
these patches.  Generally, there is no guarantee that they'll read
lkml.

On Thu, Sep 19, 2002 at 06:35:06PM -0400, Karim Yaghmour wrote:
> diff -urpN linux-2.5.36/arch/arm/kernel/entry-common.S linux-2.5.36-ltt/arch/arm/kernel/entry-common.S
> --- linux-2.5.36/arch/arm/kernel/entry-common.S	Tue Sep 17 20:58:42 2002
> +++ linux-2.5.36-ltt/arch/arm/kernel/entry-common.S	Thu Sep 19 16:29:55 2002
> @@ -35,6 +35,11 @@ ENTRY(__do_softirq)
>   * stack.
>   */
>  ret_fast_syscall:
> +#if (CONFIG_TRACE || CONFIG_TRACE_MODULE)
> +	mov	r7, r0				@ save returned r0
> +	bl	SYMBOL_NAME(trace_real_syscall_exit)
> +	mov	r0, r7
> +#endif

This misses the slow syscall exit path.

> +#if (CONFIG_TRACE || CONFIG_TRACE_MODULE)
> +asmlinkage void trace_real_syscall_entry(int scno,struct pt_regs * regs)
> +{
> +	int			depth = 0;
> +	unsigned long           end_code;
> +	unsigned long		*fp;			/* frame pointer */
> +	unsigned long		lower_bound;
> +	unsigned long		lr;			/* link register */
> +	unsigned long		*prev_fp;
> +	int			seek_depth;
> +	unsigned long           start_code;
> +	unsigned long           *start_stack;
> +	trace_syscall_entry	trace_syscall_event;
> +	unsigned long		upper_bound;
> +	int			use_bounds;
> +	int			use_depth;
> +
> +	trace_syscall_event.syscall_id = (uint8_t)scno;
> +	trace_syscall_event.address    = instruction_pointer(regs);
> +	
> +	if (! (user_mode(regs) ))
> +		goto trace_syscall_end;
> +
> +	if (trace_get_config(&use_depth,
> +			     &use_bounds,
> +			     &seek_depth,
> +			     (void*)&lower_bound,
> +			     (void*)&upper_bound) < 0)
> +		goto trace_syscall_end;
> +
> +	if ((use_depth == 1) || (use_bounds == 1)) {
> +		fp          = (unsigned long *)regs->ARM_fp;

You can't rely on FP being set to anything real.  Although the "APCS"
ABI defines that FP will be either zero or a pointer to a valid frame,
this isn't always true; a binary built with -fomit-frame-pointer will
use FP for its own purposes.  This means that there exists the possibility
for a program without any frames on the stack (although we could be
many functions deep within the program.)

Do you care about this?

-- 
Russell King (rmk@arm.linux.org.uk)                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html