Hi!
On Wed, Apr 15, 2020 at 09:20:26AM +0000, Christophe Leroy wrote:
> At the time being, __put_user()/__get_user() and friends only use
> register indirect with immediate index addressing, with the index
> set to 0. Ex:
>
> lwz reg1, 0(reg2)
This is called a "D-form" instruction, or sometimes "offset addressing".
Don't talk about an "index", it confuses things, because the *other*
kind is called "indexed" already, also in the ISA docs! (X-form, aka
indexed addressing, [reg+reg], where D-form does [reg+imm], and both
forms can do [reg]).
> Give the compiler the opportunity to use other adressing modes
> whenever possible, to get more optimised code.
Great :-)
> --- a/arch/powerpc/include/asm/uaccess.h
> +++ b/arch/powerpc/include/asm/uaccess.h
> @@ -114,7 +114,7 @@ extern long __put_user_bad(void);
> */
> #define __put_user_asm(x, addr, err, op) \
> __asm__ __volatile__( \
> - "1: " op " %1,0(%2) # put_user\n" \
> + "1: " op "%U2%X2 %1,%2 # put_user\n" \
> "2:\n" \
> ".section .fixup,\"ax\"\n" \
> "3: li %0,%3\n" \
> @@ -122,7 +122,7 @@ extern long __put_user_bad(void);
> ".previous\n" \
> EX_TABLE(1b, 3b) \
> : "=r" (err) \
> - : "r" (x), "b" (addr), "i" (-EFAULT), "0" (err))
> + : "r" (x), "m" (*addr), "i" (-EFAULT), "0" (err))
%Un on an "m" operand doesn't do much: you need to make it "m<>" if you
want pre-modify ("update") insns to be generated. (You then will want
to make sure that operand is used in a way GCC can understand; since it
is used only once here, that works fine).
> @@ -130,8 +130,8 @@ extern long __put_user_bad(void);
> #else /* __powerpc64__ */
> #define __put_user_asm2(x, addr, err) \
> __asm__ __volatile__( \
> - "1: stw %1,0(%2)\n" \
> - "2: stw %1+1,4(%2)\n" \
> + "1: stw%U2%X2 %1,%2\n" \
> + "2: stw%U2%X2 %L1,%L2\n" \
> "3:\n" \
> ".section .fixup,\"ax\"\n" \
> "4: li %0,%3\n" \
> @@ -140,7 +140,7 @@ extern long __put_user_bad(void);
> EX_TABLE(1b, 4b) \
> EX_TABLE(2b, 4b) \
> : "=r" (err) \
> - : "r" (x), "b" (addr), "i" (-EFAULT), "0" (err))
> + : "r" (x), "m" (*addr), "i" (-EFAULT), "0" (err))
Here, it doesn't work. You don't want two consecutive update insns in
any case. Easiest is to just not use "m<>", and then, don't use %Un
(which won't do anything, but it is confusing).
Same for the reads.
Rest looks fine, and update should be good with that fixed as said.
Reviewed-by: Segher Boessenkool <seg...@kernel.crashing.org>
Segher
