[PATCH] uml: use correct register file size everywhere

This patch uses MAX_REG_NR consistently to refer to the register file size.
 FRAME_SIZE isn't sufficient because on x86_64, it is smaller than the
ptrace register file size.  MAX_REG_NR was introduced as a consistent way
to get the number of registers, but wasn't used everywhere it should be.

When this causes a problem, it makes PTRACE_SETREGS fail on x86_64 because
of a corrupted segment register value in the known-good register file.  The
patch also adds a register dump at that point in case there are any future
problems here.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/um/include/sysdep-x86_64/ptrace.h

@@ -104,10 +104,6 @@ union uml_pt_regs {
 #endif
 #ifdef UML_CONFIG_MODE_SKAS
 	struct skas_regs {
-		/* x86_64 ptrace uses sizeof(user_regs_struct) as its register
-		 * file size, while i386 uses FRAME_SIZE.  Therefore, we need
-		 * to use UM_FRAME_SIZE here instead of HOST_FRAME_SIZE.
-		 */
 		unsigned long regs[MAX_REG_NR];
 		unsigned long fp[HOST_FP_SIZE];
                 struct faultinfo faultinfo;