[RFC 02/10] arm: kdump: implement crash_setup_regs()

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Mon, Mar 29, 2010 at 12:26:28PM +0300, Mika Westerberg wrote:
> Implement machine specific function crash_setup_regs() which is responsible for
> storing machine state when crash occured.

Slightly concerned about this...

> +	} else {
> +		__asm__ __volatile__("mov %0, r0" : "=r"(newregs->ARM_r0));
> +		__asm__ __volatile__("mov %0, r1" : "=r"(newregs->ARM_r1));
> +		__asm__ __volatile__("mov %0, r2" : "=r"(newregs->ARM_r2));
> +		__asm__ __volatile__("mov %0, r3" : "=r"(newregs->ARM_r3));
> +		__asm__ __volatile__("mov %0, r4" : "=r"(newregs->ARM_r4));
> +		__asm__ __volatile__("mov %0, r5" : "=r"(newregs->ARM_r5));
> +		__asm__ __volatile__("mov %0, r6" : "=r"(newregs->ARM_r6));
> +		__asm__ __volatile__("mov %0, r7" : "=r"(newregs->ARM_r7));
> +		__asm__ __volatile__("mov %0, r8" : "=r"(newregs->ARM_r8));
> +		__asm__ __volatile__("mov %0, r9" : "=r"(newregs->ARM_r9));
> +		__asm__ __volatile__("mov %0, r10" : "=r"(newregs->ARM_r10));
> +		__asm__ __volatile__("mov %0, r11" : "=r"(newregs->ARM_fp));
> +		__asm__ __volatile__("mov %0, r12" : "=r"(newregs->ARM_ip));
> +		__asm__ __volatile__("mov %0, r13" : "=r"(newregs->ARM_sp));
> +		__asm__ __volatile__("mov %0, r14" : "=r"(newregs->ARM_lr));
> +		__asm__ __volatile__("mov %0, r15" : "=r"(newregs->ARM_pc));
> + 		__asm__ __volatile__("mrs %0, cpsr" : "=r"(newregs->ARM_cpsr));

How is whatever follows on supposed to work back from this state?  It's
entirely possible that the compiler will generate a load of asm between
each __asm__ statement corrupting the registers - and you can't save
all this state without having one register storing the 'newregs'
pointer.

It'd probably be better to do something like:

	__asm__ __volatile__("stmia %0, {r0 - r15}" : : "r" (&newregs->ARM_r0));
	__asm__ __volatile__("mrs %0, cpsr" : "=r" (newregs->ARM_cpsr));

instead, which should mean only one register is (potentially) corrupted.
However, I still think you're going to have problems knowing what's in
each register.