[3/6] arm64: uaccess: Untie the input address in __range_ok
diff mbox series

Message ID 20200311180416.6509-4-richard.henderson@linaro.org
State New
Headers show
Series
  • arm64: gcc asm flag outputs
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Commit Message

Richard Henderson March 11, 2020, 6:04 p.m. UTC
There's no reason for the input address to match the output
register.  Give the register allocator a bit more freedom.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 arch/arm64/include/asm/uaccess.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Robin Murphy March 11, 2020, 7:08 p.m. UTC | #1
On 11/03/2020 6:04 pm, Richard Henderson wrote:
> There's no reason for the input address to match the output
> register.  Give the register allocator a bit more freedom.

See commit 9085b34d0e83 - as originally written they *were* the same 
operand, and this was just some impedance-matching for types. However, I 
suppose this might save a mov to initialise "ret" in the 
!CONFIG_ARM64_TAGGED_ADDR_ABI case where the original value of "addr" is 
still live for subsequent use, so it's probably reasonable. On the other 
hand, the naming only reinforces my previous complaint - now we have 
"addr_in" corresponding to "addr", and "addr" bearing no relation to 
either of those :(

Robin.

> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>   arch/arm64/include/asm/uaccess.h | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index ceb1d79eab09..fe3dd70e901e 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -75,7 +75,7 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si
>   	asm volatile(
>   	// A + B <= C + 1 for all A,B,C, in four easy steps:
>   	// 1: X = A + B; X' = X % 2^64
> -	"	adds	%[addr], %[addr], %[size]\n"
> +	"	adds	%[addr], %[addr_in], %[size]\n"
>   	// 2: Set C = 0 if X > 2^64, to guarantee X' > C in step 4
>   	"	csel	%[limit], xzr, %[limit], hi\n"
>   	// 3: Set X' = ~0 if X >= 2^64. For X == 2^64, this decrements X'
> @@ -88,7 +88,7 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si
>   	"	sbcs	xzr, %[addr], %[limit]\n"
>   	"       cset    %[addr], ls\n"
>   	: [addr] "=&r" (ret), [limit] "+r" (limit)
> -	: [size] "Ir" (size), "0" (addr)
> +	: [size] "Ir" (size), [addr_in] "r" (addr)
>   	: "cc");
>   
>   	return ret;
>

Patch
diff mbox series

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index ceb1d79eab09..fe3dd70e901e 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -75,7 +75,7 @@  static inline unsigned long __range_ok(const void __user *addr, unsigned long si
 	asm volatile(
 	// A + B <= C + 1 for all A,B,C, in four easy steps:
 	// 1: X = A + B; X' = X % 2^64
-	"	adds	%[addr], %[addr], %[size]\n"
+	"	adds	%[addr], %[addr_in], %[size]\n"
 	// 2: Set C = 0 if X > 2^64, to guarantee X' > C in step 4
 	"	csel	%[limit], xzr, %[limit], hi\n"
 	// 3: Set X' = ~0 if X >= 2^64. For X == 2^64, this decrements X'
@@ -88,7 +88,7 @@  static inline unsigned long __range_ok(const void __user *addr, unsigned long si
 	"	sbcs	xzr, %[addr], %[limit]\n"
 	"       cset    %[addr], ls\n"
 	: [addr] "=&r" (ret), [limit] "+r" (limit)
-	: [size] "Ir" (size), "0" (addr)
+	: [size] "Ir" (size), [addr_in] "r" (addr)
 	: "cc");
 
 	return ret;