x86/dumpstack: Simplify in_exception_stack()

#include <asm/stacktrace.h>

#define N_EXCEPTION_STACKS_END \

		(N_EXCEPTION_STACKS + DEBUG_STKSZ/EXCEPTION_STKSZ - 2)

static char x86_stack_ids[][8] = {

		[ DEBUG_STACK-1			]	= "#DB",

		[ NMI_STACK-1			]	= "NMI",

static char *exception_stack_names[N_EXCEPTION_STACKS] = {

		[ DOUBLEFAULT_STACK-1	]	= "#DF",

		[ NMI_STACK-1		]	= "NMI",

		[ DEBUG_STACK-1		]	= "#DB",

		[ MCE_STACK-1		]	= "#MC",

#if DEBUG_STKSZ > EXCEPTION_STKSZ

		[ N_EXCEPTION_STACKS ...

		  N_EXCEPTION_STACKS_END	]	= "#DB[?]"

#endif

};

static unsigned long exception_stack_sizes[N_EXCEPTION_STACKS] = {

	[0 ... N_EXCEPTION_STACKS - 1]		= EXCEPTION_STKSZ,

	[DEBUG_STACK - 1]			= DEBUG_STKSZ

};

static unsigned long *in_exception_stack(unsigned long stack, unsigned *usedp,

					 char **idp)

{

	unsigned long begin, end;

	unsigned k;

	/*

	 * Iterate over all exception stacks, and figure out whether

	 * 'stack' is in one of them:

	 */

	BUILD_BUG_ON(N_EXCEPTION_STACKS != 4);

	for (k = 0; k < N_EXCEPTION_STACKS; k++) {

		unsigned long end = raw_cpu_ptr(&orig_ist)->ist[k];

		/*

		 * Is 'stack' above this exception frame's end?

		 * If yes then skip to the next frame.

		 */

		if (stack >= end)

		end   = raw_cpu_ptr(&orig_ist)->ist[k];

		begin = end - exception_stack_sizes[k];

		if (stack < begin || stack >= end)

			continue;

		/*

		 * Is 'stack' above this exception frame's start address?

		 * If yes then we found the right frame.

		 */

		if (stack >= end - EXCEPTION_STKSZ) {

			/*

			 * Make sure we only iterate through an exception

			 * stack once. If it comes up for the second time

			 * then there's something wrong going on - just

			 * break out and return NULL:

		 * Make sure we only iterate through an exception stack once.

		 * If it comes up for the second time then there's something

		 * wrong going on - just break and return NULL:

		 */

		if (*usedp & (1U << k))

			break;

		*usedp |= 1U << k;

			*idp = x86_stack_ids[k];

			return (unsigned long *)end;

		}

		/*

		 * If this is a debug stack, and if it has a larger size than

		 * the usual exception stacks, then 'stack' might still

		 * be within the lower portion of the debug stack:

		 */

#if DEBUG_STKSZ > EXCEPTION_STKSZ

		if (k == DEBUG_STACK - 1 && stack >= end - DEBUG_STKSZ) {

			unsigned j = N_EXCEPTION_STACKS - 1;

			/*

			 * Black magic. A large debug stack is composed of

			 * multiple exception stack entries, which we

			 * iterate through now. Dont look:

			 */

			do {

				++j;

				end -= EXCEPTION_STKSZ;

				x86_stack_ids[j][4] = '1' +

						(j - N_EXCEPTION_STACKS);

			} while (stack < end - EXCEPTION_STKSZ);

			if (*usedp & (1U << j))

				break;

			*usedp |= 1U << j;

			*idp = x86_stack_ids[j];

		*idp = exception_stack_names[k];

		return (unsigned long *)end;

	}

#endif

	}

	return NULL;

}