Re: [patch] kprobes: dont steal interrupts from vm86

[Andi Kleen <ak@muc.de>]

Prasanna S Panchamukhi <prasanna@in.ibm.com> writes:


> +	/* Check if the application is using LDT entry for its code segment and
> +	 * calculate the address by reading the base address from the LDT entry.
> +	 */
> +	if ((regs->xcs & 4) && (current->mm)) {
> +		lp = (unsigned long *) ((unsigned long)((regs->xcs >> 3) * 8)
> +					+ (char *) current->mm->context.ldt);
> +		addr = (kprobe_opcode_t *) ((((*lp) >> 16 &  0x0000ffff)
> +				| (*(lp +1) & 0xff000000)
> +				| ((*(lp +1) << 16) & 0x00ff0000))
> +				+ regs->eip - sizeof(kprobe_opcode_t));
> +	} else {
> +		addr = (kprobe_opcode_t *)(regs->eip - sizeof(kprobe_opcode_t));
> +	}

With that patch we would have LDT reading code three times in the kernel
now (ptrace, prefetch workaround and now this). How about you factor
this out into a common helper function? This stuff is tricky enough
that there are likely bugs in there anyways and it would be best 
to only fix them at one place then.

-Andi