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

Russell King (rmk@arm.linux.org.uk)
Fri, 20 Sep 2002 00:15:00 +0100


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

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