Re: [PATCH] Add 64-bit get_user and __get_user for i386

[Linus Torvalds <torvalds@osdl.org>]

On Mon, 19 Apr 2004, Jamie Lokier wrote:
> 
> Subject: [PATCH] Add 64-bit get_user and __get_user for i386
> Patch: uaccess64-2.6.5
> 
> Add 64-bit get_user and __get_user for i386.
> Don't ask me how, but this shrinks the kernel too.

There must be some bug somewhere if the kernel shrinks from this. Although 
possibly the bug is in gcc ;)

Anyway, please don't do it like this (ie making one case be just a
memcpy). If we do this, let's do it right - ie 'd much rather see
something like

	#define get_user(x, ptr)					\
	({ __typeof__(*(ptr)) __val_gu;					\
	   int __ret_gu;						\
	   switch (sizeof(__val_gu)) {					\
	   case 1: __get_user_x(1,__ret_gu,__val_gu,ptr); break;	\
	   case 2: __get_user_x(2,__ret_gu,__val_gu,ptr); break;	\
	   case 4: __get_user_x(4,__ret_gu,__val_gu,ptr); break;	\
	   case 8: __get_user_8(__ret_gu,__val_gu,ptr); break;		\
	   default: __get_user_bad(); break;				\
	   }								\
	   (x) = __val_gu;						\
	   __ret_gu;							\
	})

and then you just make "__get_user_8()" look something like

	#define __get_user_8(ret,x,ptr)				\
		__asm__ __volatile__("call __get_user_8"	\
			:"=A" (ret), "=c" (x)			\
			:"1" (ptr))

Which is _different_ from the other "get_user" cases: it passes the 
address in %ecx, and it returns the error in %ecx too - the return value 
comes in %edx:%eax. Make the __get_user_8 in getuser.S match those 
different rules.

What do you think?

			Linus