[PATCH v3] sh: fix inline asm strncpy()

[PATCH v3] sh: fix inline asm strncpy()

[Karl Nasrallah]

The SH asm strncpy() implementation does not pad arrays with null bytes
when the size passed in is larger than than the size of the input string
(e.g. if the size of a larger destination array is passed in). Under
certain targets, it also generates 'array boundary exceeded' warnings.
This patch updates the extended asm function to address both of those
issues, and allows strncpy() to behave as described by the strncpy()
manual page.

Signed-off-by: Karl Nasrallah <knnspeed@aol.com>
---

Please note: This is an improved version of my prior code, tested
standalone with sh4-elf-gcc 9.2.0 and a Sega Dreamcast (SH7750/R-like).

If anyone is interested in an easier-to-read version of the assembly that
does not match the in-kernel style, it is included in this note:

static inline char *strncpy(char *__dest, const char *__src, size_t __n)
{
	char * retval = __dest;
	const char * __dest_end = __dest + __n - 1;

	if(__n = 0)
	{
		return retval;
	}

	__asm__ __volatile__(
	"strncpy_start:\n\t"
		"mov.b @%[src]+,r0\n\t"
		"mov.b r0,@%[dest]\n\t"
		"cmp/eq %[dest],%[dest_end]\n\t"
		"bt.s strncpy_end\n\t"
		"cmp/eq #0,r0\n\t"
		"bf.s strncpy_start\n\t"
		"add #1,%[dest]\n\t"
	"strncpy_pad:\n\t"
		"mov.b r0,@%[dest]\n\t"
		"cmp/eq %[dest],%[dest_end]\n\t"
		"bf.s strncpy_pad\n\t"
		"add #1,%[dest]\n\t"
	"strncpy_end:\n\t"
		: [dest] "+r" (__dest), [src] "+r" (__src)
		: [dest_end] "r" (__dest_end)
		: "r0","t","memory");

	return retval;
}

(In maintaining the spirit of the original work, consider this piece of
code public domain.)

 arch/sh/include/asm/string_32.h | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/sh/include/asm/string_32.h b/arch/sh/include/asm/string_32.h
index 3558b1d7123e..7f83eaea987a 100644
--- a/arch/sh/include/asm/string_32.h
+++ b/arch/sh/include/asm/string_32.h
@@ -32,6 +32,7 @@ static inline char *strcpy(char *__dest, const char *__src)
 static inline char *strncpy(char *__dest, const char *__src, size_t __n)
 {
 	register char *__xdest = __dest;
+	const char *__dest_end = __dest + __n - 1;
 	unsigned long __dummy;
 
 	if (__n = 0)
@@ -41,14 +42,19 @@ static inline char *strncpy(char *__dest, const char *__src, size_t __n)
 		"1:\n"
 		"mov.b	@%1+, %2\n\t"
 		"mov.b	%2, @%0\n\t"
-		"cmp/eq	#0, %2\n\t"
-		"bt/s	2f\n\t"
-		" cmp/eq	%5,%1\n\t"
-		"bf/s	1b\n\t"
+		"cmp/eq	%0, %5\n\t"
+		"bt.s	3f\n\t"
+		" cmp/eq	#0, %2\n\t"
+		"bf.s	1b\n\t"
 		" add	#1, %0\n"
-		"2:"
+		"2:\n\t"
+		"mov.b	%2,	@%0\n\t"
+		"cmp/eq	%0,	%5\n\t"
+		"bf.s 2b\n\t"
+		" add	#1,	%0\n"
+		"3:"
 		: "=r" (__dest), "=r" (__src), "=&z" (__dummy)
-		: "0" (__dest), "1" (__src), "r" (__src+__n)
+		: "0" (__dest), "1" (__src), "r" (__dest_end)
 		: "memory", "t");
 
 	return __xdest;
-- 
2.17.1

Re: [PATCH v3] sh: fix inline asm strncpy()

[John Paul Adrian Glaubitz]

Hi Rich!

I just noticed this patch that got posted without any reply.

Should we consider this patch?

Adrian

On 12/19/19 4:19 AM, Karl Nasrallah wrote:
> The SH asm strncpy() implementation does not pad arrays with null bytes
> when the size passed in is larger than than the size of the input string
> (e.g. if the size of a larger destination array is passed in). Under
> certain targets, it also generates 'array boundary exceeded' warnings.
> This patch updates the extended asm function to address both of those
> issues, and allows strncpy() to behave as described by the strncpy()
> manual page.
> 
> Signed-off-by: Karl Nasrallah <knnspeed@aol.com>
> ---
> 
> Please note: This is an improved version of my prior code, tested
> standalone with sh4-elf-gcc 9.2.0 and a Sega Dreamcast (SH7750/R-like).
> 
> If anyone is interested in an easier-to-read version of the assembly that
> does not match the in-kernel style, it is included in this note:
> 
> static inline char *strncpy(char *__dest, const char *__src, size_t __n)
> {
> 	char * retval = __dest;
> 	const char * __dest_end = __dest + __n - 1;
> 
> 	if(__n = 0)
> 	{
> 		return retval;
> 	}
> 
> 	__asm__ __volatile__(
> 	"strncpy_start:\n\t"
> 		"mov.b @%[src]+,r0\n\t"
> 		"mov.b r0,@%[dest]\n\t"
> 		"cmp/eq %[dest],%[dest_end]\n\t"
> 		"bt.s strncpy_end\n\t"
> 		"cmp/eq #0,r0\n\t"
> 		"bf.s strncpy_start\n\t"
> 		"add #1,%[dest]\n\t"
> 	"strncpy_pad:\n\t"
> 		"mov.b r0,@%[dest]\n\t"
> 		"cmp/eq %[dest],%[dest_end]\n\t"
> 		"bf.s strncpy_pad\n\t"
> 		"add #1,%[dest]\n\t"
> 	"strncpy_end:\n\t"
> 		: [dest] "+r" (__dest), [src] "+r" (__src)
> 		: [dest_end] "r" (__dest_end)
> 		: "r0","t","memory");
> 
> 	return retval;
> }
> 
> (In maintaining the spirit of the original work, consider this piece of
> code public domain.)
> 
>  arch/sh/include/asm/string_32.h | 18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/sh/include/asm/string_32.h b/arch/sh/include/asm/string_32.h
> index 3558b1d7123e..7f83eaea987a 100644
> --- a/arch/sh/include/asm/string_32.h
> +++ b/arch/sh/include/asm/string_32.h
> @@ -32,6 +32,7 @@ static inline char *strcpy(char *__dest, const char *__src)
>  static inline char *strncpy(char *__dest, const char *__src, size_t __n)
>  {
>  	register char *__xdest = __dest;
> +	const char *__dest_end = __dest + __n - 1;
>  	unsigned long __dummy;
>  
>  	if (__n = 0)
> @@ -41,14 +42,19 @@ static inline char *strncpy(char *__dest, const char *__src, size_t __n)
>  		"1:\n"
>  		"mov.b	@%1+, %2\n\t"
>  		"mov.b	%2, @%0\n\t"
> -		"cmp/eq	#0, %2\n\t"
> -		"bt/s	2f\n\t"
> -		" cmp/eq	%5,%1\n\t"
> -		"bf/s	1b\n\t"
> +		"cmp/eq	%0, %5\n\t"
> +		"bt.s	3f\n\t"
> +		" cmp/eq	#0, %2\n\t"
> +		"bf.s	1b\n\t"
>  		" add	#1, %0\n"
> -		"2:"
> +		"2:\n\t"
> +		"mov.b	%2,	@%0\n\t"
> +		"cmp/eq	%0,	%5\n\t"
> +		"bf.s 2b\n\t"
> +		" add	#1,	%0\n"
> +		"3:"
>  		: "=r" (__dest), "=r" (__src), "=&z" (__dummy)
> -		: "0" (__dest), "1" (__src), "r" (__src+__n)
> +		: "0" (__dest), "1" (__src), "r" (__dest_end)
>  		: "memory", "t");
>  
>  	return __xdest;
> 

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer - glaubitz@debian.org
`. `'   Freie Universitaet Berlin - glaubitz@physik.fu-berlin.de
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913

Re: [PATCH v3] sh: fix inline asm strncpy()

[John Paul Adrian Glaubitz]

On 6/7/20 2:36 PM, John Paul Adrian Glaubitz wrote:
> I just noticed this patch that got posted without any reply.
See also this discussion [1].

Adrian

> [1] https://marc.info/?l=linux-sh&m\x157671844807760&w=2

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer - glaubitz@debian.org
`. `'   Freie Universitaet Berlin - glaubitz@physik.fu-berlin.de
  `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913