[v3,13/14] RISC-V: add infrastructure to allow different str* implementations

Commit Message

Heiko Stübner Nov. 30, 2022, 10:56 p.m. UTC

From: Heiko Stuebner <[e-mail]>

Depending on supported extensions on specific RISC-V cores,
optimized str* functions might make sense.

This adds basic infrastructure to allow patching the function calls
via alternatives later on.

The main idea is to have the core str* functions be inline functions
which then call the most optimized variant and this call then be
replaced via alternatives.

The big advantage is that we don't need additional calls.
Though we need to duplicate the generic functions as the main code
expects either itself or the architecture to provide the str* functions.

The added *_generic functions are done in assembler (taken from
disassembling the main-kernel functions for now) to allow us to control
the used registers.

Reviewed-by: Conor Dooley <[e-mail]>
Signed-off-by: Heiko Stuebner <[e-mail]>
---
 arch/riscv/Makefile             |  3 ++
 arch/riscv/include/asm/string.h | 66 +++++++++++++++++++++++++++++++++
 arch/riscv/kernel/image-vars.h  |  6 +--
 arch/riscv/lib/Makefile         |  3 ++
 arch/riscv/lib/strcmp.S         | 38 +++++++++++++++++++
 arch/riscv/lib/strlen.S         | 29 +++++++++++++++
 arch/riscv/lib/strncmp.S        | 41 ++++++++++++++++++++
 7 files changed, 183 insertions(+), 3 deletions(-)
 create mode 100644 arch/riscv/lib/strcmp.S
 create mode 100644 arch/riscv/lib/strlen.S
 create mode 100644 arch/riscv/lib/strncmp.S

Comments

Andrew Jones Dec. 1, 2022, 8:07 p.m. UTC | #1

On Wed, Nov 30, 2022 at 11:56:13PM +0100, Heiko Stuebner wrote:
> From: Heiko Stuebner <[e-mail]>
> 
> Depending on supported extensions on specific RISC-V cores,
> optimized str* functions might make sense.
> 
> This adds basic infrastructure to allow patching the function calls
> via alternatives later on.
> 
> The main idea is to have the core str* functions be inline functions
> which then call the most optimized variant and this call then be
> replaced via alternatives.
> 
> The big advantage is that we don't need additional calls.
> Though we need to duplicate the generic functions as the main code
> expects either itself or the architecture to provide the str* functions.

That's a bummer, but at least the duplicated functions are simple.

> 
> The added *_generic functions are done in assembler (taken from
> disassembling the main-kernel functions for now) to allow us to control
> the used registers.
> 
> Reviewed-by: Conor Dooley <[e-mail]>
> Signed-off-by: Heiko Stuebner <[e-mail]>
> ---
>  arch/riscv/Makefile             |  3 ++
>  arch/riscv/include/asm/string.h | 66 +++++++++++++++++++++++++++++++++
>  arch/riscv/kernel/image-vars.h  |  6 +--
>  arch/riscv/lib/Makefile         |  3 ++
>  arch/riscv/lib/strcmp.S         | 38 +++++++++++++++++++
>  arch/riscv/lib/strlen.S         | 29 +++++++++++++++
>  arch/riscv/lib/strncmp.S        | 41 ++++++++++++++++++++
>  7 files changed, 183 insertions(+), 3 deletions(-)
>  create mode 100644 arch/riscv/lib/strcmp.S
>  create mode 100644 arch/riscv/lib/strlen.S
>  create mode 100644 arch/riscv/lib/strncmp.S
> 
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index 0d13b597cb55..581e4370c2a6 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -80,6 +80,9 @@ ifeq ($(CONFIG_PERF_EVENTS),y)
>          KBUILD_CFLAGS += -fno-omit-frame-pointer
>  endif
>  
> +# strchr is special case, as gcc might want to call its own strlen from there
> +KBUILD_CFLAGS += -fno-builtin-strlen -fno-builtin-strcmp -fno-builtin-strncmp -fno-builtin-strchr
> +
>  KBUILD_CFLAGS_MODULE += $(call cc-option,-mno-relax)
>  KBUILD_AFLAGS_MODULE += $(call as-option,-Wa$(comma)-mno-relax)
>  
> diff --git a/arch/riscv/include/asm/string.h b/arch/riscv/include/asm/string.h
> index 909049366555..b98481d2d154 100644
> --- a/arch/riscv/include/asm/string.h
> +++ b/arch/riscv/include/asm/string.h
> @@ -18,6 +18,72 @@ extern asmlinkage void *__memcpy(void *, const void *, size_t);
>  #define __HAVE_ARCH_MEMMOVE
>  extern asmlinkage void *memmove(void *, const void *, size_t);
>  extern asmlinkage void *__memmove(void *, const void *, size_t);
> +
> +#define __HAVE_ARCH_STRCMP
> +extern asmlinkage int __strcmp_generic(const char *cs, const char *ct);
> +
> +static inline int strcmp(const char *cs, const char *ct)
> +{
> +#ifdef RISCV_EFISTUB
> +	return __strcmp_generic(cs, ct);
> +#else
> +	register const char *a0 asm("a0") = cs;
> +	register const char *a1 asm("a1") = ct;
> +	register int a0_out asm("a0");
> +
> +	asm volatile("call __strcmp_generic\n\t"
> +		: "=r"(a0_out)
> +		: "r"(a0), "r"(a1)
> +		: "ra", "t0", "t1", "t2");
> +
> +	return a0_out;
> +#endif
> +}
> +
> +#define __HAVE_ARCH_STRNCMP
> +extern asmlinkage int __strncmp_generic(const char *cs,
> +					const char *ct, size_t count);
> +
> +static inline int strncmp(const char *cs, const char *ct, size_t count)
> +{
> +#ifdef RISCV_EFISTUB
> +	return __strncmp_generic(cs, ct, count);
> +#else
> +	register const char *a0 asm("a0") = cs;
> +	register const char *a1 asm("a1") = ct;
> +	register size_t a2 asm("a2") = count;
> +	register int a0_out asm("a0");
> +
> +	asm volatile("call __strncmp_generic\n\t"
> +		: "=r"(a0_out)
> +		: "r"(a0), "r"(a1), "r"(a2)
> +		: "ra", "t0", "t1", "t2");
> +
> +	return a0_out;
> +#endif
> +}
> +
> +#define __HAVE_ARCH_STRLEN
> +extern asmlinkage __kernel_size_t __strlen_generic(const char *);
> +
> +static inline __kernel_size_t strlen(const char *s)
> +{
> +#ifdef RISCV_EFISTUB
> +	return __strlen_generic(s);
> +#else
> +	register const char *a0 asm("a0") = s;
> +	register int a0_out asm("a0");
> +
> +	asm volatile(
> +		"call __strlen_generic\n\t"
> +		: "=r"(a0_out)
> +		: "r"(a0)
> +		: "ra", "t0", "t1");
> +
> +	return a0_out;
> +#endif
> +}
> +
>  /* For those files which don't want to check by kasan. */
>  #if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
>  #define memcpy(dst, src, len) __memcpy(dst, src, len)
> diff --git a/arch/riscv/kernel/image-vars.h b/arch/riscv/kernel/image-vars.h
> index d6e5f739905e..2f270b9fde63 100644
> --- a/arch/riscv/kernel/image-vars.h
> +++ b/arch/riscv/kernel/image-vars.h
> @@ -25,10 +25,10 @@
>   */
>  __efistub_memcmp		= memcmp;
>  __efistub_memchr		= memchr;
> -__efistub_strlen		= strlen;
> +__efistub___strlen_generic	= __strlen_generic;
>  __efistub_strnlen		= strnlen;
> -__efistub_strcmp		= strcmp;
> -__efistub_strncmp		= strncmp;
> +__efistub___strcmp_generic	= __strcmp_generic;
> +__efistub___strncmp_generic	= __strncmp_generic;
>  __efistub_strrchr		= strrchr;
>  
>  __efistub__start		= _start;
> diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
> index 25d5c9664e57..6c74b0bedd60 100644
> --- a/arch/riscv/lib/Makefile
> +++ b/arch/riscv/lib/Makefile
> @@ -3,6 +3,9 @@ lib-y			+= delay.o
>  lib-y			+= memcpy.o
>  lib-y			+= memset.o
>  lib-y			+= memmove.o
> +lib-y			+= strcmp.o
> +lib-y			+= strlen.o
> +lib-y			+= strncmp.o

Can't we just create a single string.S file?

>  lib-$(CONFIG_MMU)	+= uaccess.o
>  lib-$(CONFIG_64BIT)	+= tishift.o
>  
> diff --git a/arch/riscv/lib/strcmp.S b/arch/riscv/lib/strcmp.S
> new file mode 100644
> index 000000000000..f4b7f4e806f0
> --- /dev/null
> +++ b/arch/riscv/lib/strcmp.S
> @@ -0,0 +1,38 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#include <linux/linkage.h>
> +#include <asm/asm.h>
> +#include <asm-generic/export.h>
> +
> +/* int __strcmp_generic(const char *cs, const char *ct) */
> +ENTRY(__strcmp_generic)
> +	/*
> +	 * Returns
> +	 *   a0 - comparison result, value like strcmp
> +	 *
> +	 * Parameters
> +	 *   a0 - string1
> +	 *   a1 - string2
> +	 *
> +	 * Clobbers
> +	 *   t0, t1, t2
> +	 */
> +	mv	t2, a1
> +1:
> +	lbu	t1, 0(a0)
> +	lbu	t0, 0(a1)
> +	addi	a0, a0, 1
> +	addi	a1, a1, 1
> +	beq	t1, t0, 3f
> +	li	a0, 1
> +	bgeu	t1, t0, 2f
> +	li	a0, -1
> +2:
> +	mv	a1, t2
> +	ret
> +3:
> +	bnez	t1, 1b
> +	li	a0, 0
> +	j	2b
> +END(__strcmp_generic)
> +EXPORT_SYMBOL(__strcmp_generic)
> diff --git a/arch/riscv/lib/strlen.S b/arch/riscv/lib/strlen.S
> new file mode 100644
> index 000000000000..e0e7440ac724
> --- /dev/null
> +++ b/arch/riscv/lib/strlen.S
> @@ -0,0 +1,29 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#include <linux/linkage.h>
> +#include <asm/asm.h>
> +#include <asm-generic/export.h>
> +
> +/* int __strlen_generic(const char *s) */
> +ENTRY(__strlen_generic)
> +	/*
> +	 * Returns
> +	 *   a0 - string length
> +	 *
> +	 * Parameters
> +	 *   a0 - String to measure
> +	 *
> +	 * Clobbers:
> +	 *   t0, t1
> +	 */
> +	mv	t1, a0
> +1:
> +	lbu	t0, 0(t1)
> +	bnez	t0, 2f
> +	sub	a0, t1, a0
> +	ret
> +2:
> +	addi	t1, t1, 1
> +	j	1b
> +END(__strlen_generic)
> +EXPORT_SYMBOL(__strlen_generic)
> diff --git a/arch/riscv/lib/strncmp.S b/arch/riscv/lib/strncmp.S
> new file mode 100644
> index 000000000000..7e116d942265
> --- /dev/null
> +++ b/arch/riscv/lib/strncmp.S
> @@ -0,0 +1,41 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#include <linux/linkage.h>
> +#include <asm/asm.h>
> +#include <asm-generic/export.h>
> +
> +/* int __strncmp_generic(const char *cs, const char *ct, size_t count) */
> +ENTRY(__strncmp_generic)
> +	/*
> +	 * Returns
> +	 *   a0 - comparison result, value like strncmp
> +	 *
> +	 * Parameters
> +	 *   a0 - string1
> +	 *   a1 - string2
> +	 *   a2 - number of characters to compare
> +	 *
> +	 * Clobbers
> +	 *   t0, t1, t2
> +	 */
> +	li	t0, 0
> +1:
> +	beq	a2, t0, 4f
> +	add	t1, a0, t0
> +	add	t2, a1, t0
> +	lbu	t1, 0(t1)
> +	lbu	t2, 0(t2)
> +	beq	t1, t2, 3f
> +	li	a0, 1
> +	bgeu	t1, t2, 2f
> +	li	a0, -1
> +2:
> +	ret
> +3:
> +	addi	t0, t0, 1
> +	bnez	t1, 1b
> +4:
> +	li	a0, 0
> +	j	2b
> +END(__strncmp_generic)
> +EXPORT_SYMBOL(__strncmp_generic)
> -- 
> 2.35.1
>

Besides the consolidation of functions to one file request,

Reviewed-by: Andrew Jones <[e-mail]>

Thanks,
drew

Andrew Jones Dec. 1, 2022, 8:14 p.m. UTC | #2

On Thu, Dec 01, 2022 at 09:07:41PM +0100, Andrew Jones wrote:
> On Wed, Nov 30, 2022 at 11:56:13PM +0100, Heiko Stuebner wrote:
> > From: Heiko Stuebner <[e-mail]>
> > 
> > Depending on supported extensions on specific RISC-V cores,
> > optimized str* functions might make sense.
> > 
> > This adds basic infrastructure to allow patching the function calls
> > via alternatives later on.
> > 
> > The main idea is to have the core str* functions be inline functions
> > which then call the most optimized variant and this call then be
> > replaced via alternatives.
> > 
> > The big advantage is that we don't need additional calls.
> > Though we need to duplicate the generic functions as the main code
> > expects either itself or the architecture to provide the str* functions.
> 
> That's a bummer, but at least the duplicated functions are simple.
> 
> > 
> > The added *_generic functions are done in assembler (taken from
> > disassembling the main-kernel functions for now) to allow us to control
> > the used registers.
> > 
> > Reviewed-by: Conor Dooley <[e-mail]>
> > Signed-off-by: Heiko Stuebner <[e-mail]>
> > ---
> >  arch/riscv/Makefile             |  3 ++
> >  arch/riscv/include/asm/string.h | 66 +++++++++++++++++++++++++++++++++
> >  arch/riscv/kernel/image-vars.h  |  6 +--
> >  arch/riscv/lib/Makefile         |  3 ++
> >  arch/riscv/lib/strcmp.S         | 38 +++++++++++++++++++
> >  arch/riscv/lib/strlen.S         | 29 +++++++++++++++
> >  arch/riscv/lib/strncmp.S        | 41 ++++++++++++++++++++
> >  7 files changed, 183 insertions(+), 3 deletions(-)
> >  create mode 100644 arch/riscv/lib/strcmp.S
> >  create mode 100644 arch/riscv/lib/strlen.S
> >  create mode 100644 arch/riscv/lib/strncmp.S
> > 
> > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> > index 0d13b597cb55..581e4370c2a6 100644
> > --- a/arch/riscv/Makefile
> > +++ b/arch/riscv/Makefile
> > @@ -80,6 +80,9 @@ ifeq ($(CONFIG_PERF_EVENTS),y)
> >          KBUILD_CFLAGS += -fno-omit-frame-pointer
> >  endif
> >  
> > +# strchr is special case, as gcc might want to call its own strlen from there
> > +KBUILD_CFLAGS += -fno-builtin-strlen -fno-builtin-strcmp -fno-builtin-strncmp -fno-builtin-strchr
> > +
> >  KBUILD_CFLAGS_MODULE += $(call cc-option,-mno-relax)
> >  KBUILD_AFLAGS_MODULE += $(call as-option,-Wa$(comma)-mno-relax)
> >  
> > diff --git a/arch/riscv/include/asm/string.h b/arch/riscv/include/asm/string.h
> > index 909049366555..b98481d2d154 100644
> > --- a/arch/riscv/include/asm/string.h
> > +++ b/arch/riscv/include/asm/string.h
> > @@ -18,6 +18,72 @@ extern asmlinkage void *__memcpy(void *, const void *, size_t);
> >  #define __HAVE_ARCH_MEMMOVE
> >  extern asmlinkage void *memmove(void *, const void *, size_t);
> >  extern asmlinkage void *__memmove(void *, const void *, size_t);
> > +
> > +#define __HAVE_ARCH_STRCMP
> > +extern asmlinkage int __strcmp_generic(const char *cs, const char *ct);
> > +
> > +static inline int strcmp(const char *cs, const char *ct)
> > +{
> > +#ifdef RISCV_EFISTUB
> > +	return __strcmp_generic(cs, ct);
> > +#else
> > +	register const char *a0 asm("a0") = cs;
> > +	register const char *a1 asm("a1") = ct;
> > +	register int a0_out asm("a0");
> > +
> > +	asm volatile("call __strcmp_generic\n\t"
> > +		: "=r"(a0_out)
> > +		: "r"(a0), "r"(a1)
> > +		: "ra", "t0", "t1", "t2");

Don't we need "memory" in all these clobber lists?

Thanks,
drew

> > +
> > +	return a0_out;
> > +#endif
> > +}
> > +
> > +#define __HAVE_ARCH_STRNCMP
> > +extern asmlinkage int __strncmp_generic(const char *cs,
> > +					const char *ct, size_t count);
> > +
> > +static inline int strncmp(const char *cs, const char *ct, size_t count)
> > +{
> > +#ifdef RISCV_EFISTUB
> > +	return __strncmp_generic(cs, ct, count);
> > +#else
> > +	register const char *a0 asm("a0") = cs;
> > +	register const char *a1 asm("a1") = ct;
> > +	register size_t a2 asm("a2") = count;
> > +	register int a0_out asm("a0");
> > +
> > +	asm volatile("call __strncmp_generic\n\t"
> > +		: "=r"(a0_out)
> > +		: "r"(a0), "r"(a1), "r"(a2)
> > +		: "ra", "t0", "t1", "t2");
> > +
> > +	return a0_out;
> > +#endif
> > +}
> > +
> > +#define __HAVE_ARCH_STRLEN
> > +extern asmlinkage __kernel_size_t __strlen_generic(const char *);
> > +
> > +static inline __kernel_size_t strlen(const char *s)
> > +{
> > +#ifdef RISCV_EFISTUB
> > +	return __strlen_generic(s);
> > +#else
> > +	register const char *a0 asm("a0") = s;
> > +	register int a0_out asm("a0");
> > +
> > +	asm volatile(
> > +		"call __strlen_generic\n\t"
> > +		: "=r"(a0_out)
> > +		: "r"(a0)
> > +		: "ra", "t0", "t1");
> > +
> > +	return a0_out;
> > +#endif
> > +}
> > +
> >  /* For those files which don't want to check by kasan. */
> >  #if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
> >  #define memcpy(dst, src, len) __memcpy(dst, src, len)
> > diff --git a/arch/riscv/kernel/image-vars.h b/arch/riscv/kernel/image-vars.h
> > index d6e5f739905e..2f270b9fde63 100644
> > --- a/arch/riscv/kernel/image-vars.h
> > +++ b/arch/riscv/kernel/image-vars.h
> > @@ -25,10 +25,10 @@
> >   */
> >  __efistub_memcmp		= memcmp;
> >  __efistub_memchr		= memchr;
> > -__efistub_strlen		= strlen;
> > +__efistub___strlen_generic	= __strlen_generic;
> >  __efistub_strnlen		= strnlen;
> > -__efistub_strcmp		= strcmp;
> > -__efistub_strncmp		= strncmp;
> > +__efistub___strcmp_generic	= __strcmp_generic;
> > +__efistub___strncmp_generic	= __strncmp_generic;
> >  __efistub_strrchr		= strrchr;
> >  
> >  __efistub__start		= _start;
> > diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
> > index 25d5c9664e57..6c74b0bedd60 100644
> > --- a/arch/riscv/lib/Makefile
> > +++ b/arch/riscv/lib/Makefile
> > @@ -3,6 +3,9 @@ lib-y			+= delay.o
> >  lib-y			+= memcpy.o
> >  lib-y			+= memset.o
> >  lib-y			+= memmove.o
> > +lib-y			+= strcmp.o
> > +lib-y			+= strlen.o
> > +lib-y			+= strncmp.o
> 
> Can't we just create a single string.S file?
> 
> >  lib-$(CONFIG_MMU)	+= uaccess.o
> >  lib-$(CONFIG_64BIT)	+= tishift.o
> >  
> > diff --git a/arch/riscv/lib/strcmp.S b/arch/riscv/lib/strcmp.S
> > new file mode 100644
> > index 000000000000..f4b7f4e806f0
> > --- /dev/null
> > +++ b/arch/riscv/lib/strcmp.S
> > @@ -0,0 +1,38 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +
> > +#include <linux/linkage.h>
> > +#include <asm/asm.h>
> > +#include <asm-generic/export.h>
> > +
> > +/* int __strcmp_generic(const char *cs, const char *ct) */
> > +ENTRY(__strcmp_generic)
> > +	/*
> > +	 * Returns
> > +	 *   a0 - comparison result, value like strcmp
> > +	 *
> > +	 * Parameters
> > +	 *   a0 - string1
> > +	 *   a1 - string2
> > +	 *
> > +	 * Clobbers
> > +	 *   t0, t1, t2
> > +	 */
> > +	mv	t2, a1
> > +1:
> > +	lbu	t1, 0(a0)
> > +	lbu	t0, 0(a1)
> > +	addi	a0, a0, 1
> > +	addi	a1, a1, 1
> > +	beq	t1, t0, 3f
> > +	li	a0, 1
> > +	bgeu	t1, t0, 2f
> > +	li	a0, -1
> > +2:
> > +	mv	a1, t2
> > +	ret
> > +3:
> > +	bnez	t1, 1b
> > +	li	a0, 0
> > +	j	2b
> > +END(__strcmp_generic)
> > +EXPORT_SYMBOL(__strcmp_generic)
> > diff --git a/arch/riscv/lib/strlen.S b/arch/riscv/lib/strlen.S
> > new file mode 100644
> > index 000000000000..e0e7440ac724
> > --- /dev/null
> > +++ b/arch/riscv/lib/strlen.S
> > @@ -0,0 +1,29 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +
> > +#include <linux/linkage.h>
> > +#include <asm/asm.h>
> > +#include <asm-generic/export.h>
> > +
> > +/* int __strlen_generic(const char *s) */
> > +ENTRY(__strlen_generic)
> > +	/*
> > +	 * Returns
> > +	 *   a0 - string length
> > +	 *
> > +	 * Parameters
> > +	 *   a0 - String to measure
> > +	 *
> > +	 * Clobbers:
> > +	 *   t0, t1
> > +	 */
> > +	mv	t1, a0
> > +1:
> > +	lbu	t0, 0(t1)
> > +	bnez	t0, 2f
> > +	sub	a0, t1, a0
> > +	ret
> > +2:
> > +	addi	t1, t1, 1
> > +	j	1b
> > +END(__strlen_generic)
> > +EXPORT_SYMBOL(__strlen_generic)
> > diff --git a/arch/riscv/lib/strncmp.S b/arch/riscv/lib/strncmp.S
> > new file mode 100644
> > index 000000000000..7e116d942265
> > --- /dev/null
> > +++ b/arch/riscv/lib/strncmp.S
> > @@ -0,0 +1,41 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +
> > +#include <linux/linkage.h>
> > +#include <asm/asm.h>
> > +#include <asm-generic/export.h>
> > +
> > +/* int __strncmp_generic(const char *cs, const char *ct, size_t count) */
> > +ENTRY(__strncmp_generic)
> > +	/*
> > +	 * Returns
> > +	 *   a0 - comparison result, value like strncmp
> > +	 *
> > +	 * Parameters
> > +	 *   a0 - string1
> > +	 *   a1 - string2
> > +	 *   a2 - number of characters to compare
> > +	 *
> > +	 * Clobbers
> > +	 *   t0, t1, t2
> > +	 */
> > +	li	t0, 0
> > +1:
> > +	beq	a2, t0, 4f
> > +	add	t1, a0, t0
> > +	add	t2, a1, t0
> > +	lbu	t1, 0(t1)
> > +	lbu	t2, 0(t2)
> > +	beq	t1, t2, 3f
> > +	li	a0, 1
> > +	bgeu	t1, t2, 2f
> > +	li	a0, -1
> > +2:
> > +	ret
> > +3:
> > +	addi	t0, t0, 1
> > +	bnez	t1, 1b
> > +4:
> > +	li	a0, 0
> > +	j	2b
> > +END(__strncmp_generic)
> > +EXPORT_SYMBOL(__strncmp_generic)
> > -- 
> > 2.35.1
> >
> 
> Besides the consolidation of functions to one file request,
> 
> Reviewed-by: Andrew Jones <[e-mail]>
> 
> Thanks,
> drew

Palmer Dabbelt Dec. 2, 2022, 4:08 a.m. UTC | #3

On Wed, 30 Nov 2022 14:56:13 PST (-0800), [e-mail] wrote:
> From: Heiko Stuebner <[e-mail]>
>
> Depending on supported extensions on specific RISC-V cores,
> optimized str* functions might make sense.
>
> This adds basic infrastructure to allow patching the function calls
> via alternatives later on.
>
> The main idea is to have the core str* functions be inline functions
> which then call the most optimized variant and this call then be
> replaced via alternatives.
>
> The big advantage is that we don't need additional calls.
> Though we need to duplicate the generic functions as the main code
> expects either itself or the architecture to provide the str* functions.
>
> The added *_generic functions are done in assembler (taken from
> disassembling the main-kernel functions for now) to allow us to control
> the used registers.
>
> Reviewed-by: Conor Dooley <[e-mail]>
> Signed-off-by: Heiko Stuebner <[e-mail]>
> ---
>  arch/riscv/Makefile             |  3 ++
>  arch/riscv/include/asm/string.h | 66 +++++++++++++++++++++++++++++++++
>  arch/riscv/kernel/image-vars.h  |  6 +--
>  arch/riscv/lib/Makefile         |  3 ++
>  arch/riscv/lib/strcmp.S         | 38 +++++++++++++++++++
>  arch/riscv/lib/strlen.S         | 29 +++++++++++++++
>  arch/riscv/lib/strncmp.S        | 41 ++++++++++++++++++++
>  7 files changed, 183 insertions(+), 3 deletions(-)
>  create mode 100644 arch/riscv/lib/strcmp.S
>  create mode 100644 arch/riscv/lib/strlen.S
>  create mode 100644 arch/riscv/lib/strncmp.S
>
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index 0d13b597cb55..581e4370c2a6 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -80,6 +80,9 @@ ifeq ($(CONFIG_PERF_EVENTS),y)
>          KBUILD_CFLAGS += -fno-omit-frame-pointer
>  endif
>
> +# strchr is special case, as gcc might want to call its own strlen from there
> +KBUILD_CFLAGS += -fno-builtin-strlen -fno-builtin-strcmp -fno-builtin-strncmp -fno-builtin-strchr

I was poking around Ard's comment on that -DRISCV_EFI to try and figure 
out what it was doing, but I think this is the bigger issue.  I haven't 
benchmarked anything, but my guess is that turning off support for these 
builtin routines will outweigh the faster outline implementations of 
these routines.  I don't have any benchmarks to prove that, but in 
general compilers are pretty smart about handling these builtin routines 
in the common cases and deferring that to runtime is probably the wrong 
option.

I haven't looked all that closely at this patch set.  Is there some 
reason it's necessary to disable the builtin handling?  If not then my 
guess is it's better to leave that enabled unless some benchmarks show 
otherwise (and I don't know of any Zb* hardware to test against).

> +
>  KBUILD_CFLAGS_MODULE += $(call cc-option,-mno-relax)
>  KBUILD_AFLAGS_MODULE += $(call as-option,-Wa$(comma)-mno-relax)
>
> diff --git a/arch/riscv/include/asm/string.h b/arch/riscv/include/asm/string.h
> index 909049366555..b98481d2d154 100644
> --- a/arch/riscv/include/asm/string.h
> +++ b/arch/riscv/include/asm/string.h
> @@ -18,6 +18,72 @@ extern asmlinkage void *__memcpy(void *, const void *, size_t);
>  #define __HAVE_ARCH_MEMMOVE
>  extern asmlinkage void *memmove(void *, const void *, size_t);
>  extern asmlinkage void *__memmove(void *, const void *, size_t);
> +
> +#define __HAVE_ARCH_STRCMP
> +extern asmlinkage int __strcmp_generic(const char *cs, const char *ct);
> +
> +static inline int strcmp(const char *cs, const char *ct)
> +{
> +#ifdef RISCV_EFISTUB
> +	return __strcmp_generic(cs, ct);
> +#else
> +	register const char *a0 asm("a0") = cs;
> +	register const char *a1 asm("a1") = ct;
> +	register int a0_out asm("a0");
> +
> +	asm volatile("call __strcmp_generic\n\t"
> +		: "=r"(a0_out)
> +		: "r"(a0), "r"(a1)
> +		: "ra", "t0", "t1", "t2");
> +
> +	return a0_out;
> +#endif
> +}
> +
> +#define __HAVE_ARCH_STRNCMP
> +extern asmlinkage int __strncmp_generic(const char *cs,
> +					const char *ct, size_t count);
> +
> +static inline int strncmp(const char *cs, const char *ct, size_t count)
> +{
> +#ifdef RISCV_EFISTUB
> +	return __strncmp_generic(cs, ct, count);
> +#else
> +	register const char *a0 asm("a0") = cs;
> +	register const char *a1 asm("a1") = ct;
> +	register size_t a2 asm("a2") = count;
> +	register int a0_out asm("a0");
> +
> +	asm volatile("call __strncmp_generic\n\t"
> +		: "=r"(a0_out)
> +		: "r"(a0), "r"(a1), "r"(a2)
> +		: "ra", "t0", "t1", "t2");
> +
> +	return a0_out;
> +#endif
> +}
> +
> +#define __HAVE_ARCH_STRLEN
> +extern asmlinkage __kernel_size_t __strlen_generic(const char *);
> +
> +static inline __kernel_size_t strlen(const char *s)
> +{
> +#ifdef RISCV_EFISTUB
> +	return __strlen_generic(s);
> +#else
> +	register const char *a0 asm("a0") = s;
> +	register int a0_out asm("a0");
> +
> +	asm volatile(
> +		"call __strlen_generic\n\t"
> +		: "=r"(a0_out)
> +		: "r"(a0)
> +		: "ra", "t0", "t1");
> +
> +	return a0_out;
> +#endif
> +}
> +
>  /* For those files which don't want to check by kasan. */
>  #if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
>  #define memcpy(dst, src, len) __memcpy(dst, src, len)
> diff --git a/arch/riscv/kernel/image-vars.h b/arch/riscv/kernel/image-vars.h
> index d6e5f739905e..2f270b9fde63 100644
> --- a/arch/riscv/kernel/image-vars.h
> +++ b/arch/riscv/kernel/image-vars.h
> @@ -25,10 +25,10 @@
>   */
>  __efistub_memcmp		= memcmp;
>  __efistub_memchr		= memchr;
> -__efistub_strlen		= strlen;
> +__efistub___strlen_generic	= __strlen_generic;
>  __efistub_strnlen		= strnlen;
> -__efistub_strcmp		= strcmp;
> -__efistub_strncmp		= strncmp;
> +__efistub___strcmp_generic	= __strcmp_generic;
> +__efistub___strncmp_generic	= __strncmp_generic;
>  __efistub_strrchr		= strrchr;
>
>  __efistub__start		= _start;
> diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
> index 25d5c9664e57..6c74b0bedd60 100644
> --- a/arch/riscv/lib/Makefile
> +++ b/arch/riscv/lib/Makefile
> @@ -3,6 +3,9 @@ lib-y			+= delay.o
>  lib-y			+= memcpy.o
>  lib-y			+= memset.o
>  lib-y			+= memmove.o
> +lib-y			+= strcmp.o
> +lib-y			+= strlen.o
> +lib-y			+= strncmp.o
>  lib-$(CONFIG_MMU)	+= uaccess.o
>  lib-$(CONFIG_64BIT)	+= tishift.o
>
> diff --git a/arch/riscv/lib/strcmp.S b/arch/riscv/lib/strcmp.S
> new file mode 100644
> index 000000000000..f4b7f4e806f0
> --- /dev/null
> +++ b/arch/riscv/lib/strcmp.S
> @@ -0,0 +1,38 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#include <linux/linkage.h>
> +#include <asm/asm.h>
> +#include <asm-generic/export.h>
> +
> +/* int __strcmp_generic(const char *cs, const char *ct) */
> +ENTRY(__strcmp_generic)
> +	/*
> +	 * Returns
> +	 *   a0 - comparison result, value like strcmp
> +	 *
> +	 * Parameters
> +	 *   a0 - string1
> +	 *   a1 - string2
> +	 *
> +	 * Clobbers
> +	 *   t0, t1, t2
> +	 */
> +	mv	t2, a1
> +1:
> +	lbu	t1, 0(a0)
> +	lbu	t0, 0(a1)
> +	addi	a0, a0, 1
> +	addi	a1, a1, 1
> +	beq	t1, t0, 3f
> +	li	a0, 1
> +	bgeu	t1, t0, 2f
> +	li	a0, -1
> +2:
> +	mv	a1, t2
> +	ret
> +3:
> +	bnez	t1, 1b
> +	li	a0, 0
> +	j	2b
> +END(__strcmp_generic)
> +EXPORT_SYMBOL(__strcmp_generic)
> diff --git a/arch/riscv/lib/strlen.S b/arch/riscv/lib/strlen.S
> new file mode 100644
> index 000000000000..e0e7440ac724
> --- /dev/null
> +++ b/arch/riscv/lib/strlen.S
> @@ -0,0 +1,29 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#include <linux/linkage.h>
> +#include <asm/asm.h>
> +#include <asm-generic/export.h>
> +
> +/* int __strlen_generic(const char *s) */
> +ENTRY(__strlen_generic)
> +	/*
> +	 * Returns
> +	 *   a0 - string length
> +	 *
> +	 * Parameters
> +	 *   a0 - String to measure
> +	 *
> +	 * Clobbers:
> +	 *   t0, t1
> +	 */
> +	mv	t1, a0
> +1:
> +	lbu	t0, 0(t1)
> +	bnez	t0, 2f
> +	sub	a0, t1, a0
> +	ret
> +2:
> +	addi	t1, t1, 1
> +	j	1b
> +END(__strlen_generic)
> +EXPORT_SYMBOL(__strlen_generic)
> diff --git a/arch/riscv/lib/strncmp.S b/arch/riscv/lib/strncmp.S
> new file mode 100644
> index 000000000000..7e116d942265
> --- /dev/null
> +++ b/arch/riscv/lib/strncmp.S
> @@ -0,0 +1,41 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#include <linux/linkage.h>
> +#include <asm/asm.h>
> +#include <asm-generic/export.h>
> +
> +/* int __strncmp_generic(const char *cs, const char *ct, size_t count) */
> +ENTRY(__strncmp_generic)
> +	/*
> +	 * Returns
> +	 *   a0 - comparison result, value like strncmp
> +	 *
> +	 * Parameters
> +	 *   a0 - string1
> +	 *   a1 - string2
> +	 *   a2 - number of characters to compare
> +	 *
> +	 * Clobbers
> +	 *   t0, t1, t2
> +	 */
> +	li	t0, 0
> +1:
> +	beq	a2, t0, 4f
> +	add	t1, a0, t0
> +	add	t2, a1, t0
> +	lbu	t1, 0(t1)
> +	lbu	t2, 0(t2)
> +	beq	t1, t2, 3f
> +	li	a0, 1
> +	bgeu	t1, t2, 2f
> +	li	a0, -1
> +2:
> +	ret
> +3:
> +	addi	t0, t0, 1
> +	bnez	t1, 1b
> +4:
> +	li	a0, 0
> +	j	2b
> +END(__strncmp_generic)
> +EXPORT_SYMBOL(__strncmp_generic)

Ard Biesheuvel Dec. 2, 2022, 8:19 a.m. UTC | #4

On Fri, 2 Dec 2022 at 05:08, Palmer Dabbelt <[e-mail]> wrote:
>
> On Wed, 30 Nov 2022 14:56:13 PST (-0800), [e-mail] wrote:
> > From: Heiko Stuebner <[e-mail]>
> >
> > Depending on supported extensions on specific RISC-V cores,
> > optimized str* functions might make sense.
> >
> > This adds basic infrastructure to allow patching the function calls
> > via alternatives later on.
> >
> > The main idea is to have the core str* functions be inline functions
> > which then call the most optimized variant and this call then be
> > replaced via alternatives.
> >
> > The big advantage is that we don't need additional calls.
> > Though we need to duplicate the generic functions as the main code
> > expects either itself or the architecture to provide the str* functions.
> >
> > The added *_generic functions are done in assembler (taken from
> > disassembling the main-kernel functions for now) to allow us to control
> > the used registers.
> >
> > Reviewed-by: Conor Dooley <[e-mail]>
> > Signed-off-by: Heiko Stuebner <[e-mail]>
> > ---
> >  arch/riscv/Makefile             |  3 ++
> >  arch/riscv/include/asm/string.h | 66 +++++++++++++++++++++++++++++++++
> >  arch/riscv/kernel/image-vars.h  |  6 +--
> >  arch/riscv/lib/Makefile         |  3 ++
> >  arch/riscv/lib/strcmp.S         | 38 +++++++++++++++++++
> >  arch/riscv/lib/strlen.S         | 29 +++++++++++++++
> >  arch/riscv/lib/strncmp.S        | 41 ++++++++++++++++++++
> >  7 files changed, 183 insertions(+), 3 deletions(-)
> >  create mode 100644 arch/riscv/lib/strcmp.S
> >  create mode 100644 arch/riscv/lib/strlen.S
> >  create mode 100644 arch/riscv/lib/strncmp.S
> >
> > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> > index 0d13b597cb55..581e4370c2a6 100644
> > --- a/arch/riscv/Makefile
> > +++ b/arch/riscv/Makefile
> > @@ -80,6 +80,9 @@ ifeq ($(CONFIG_PERF_EVENTS),y)
> >          KBUILD_CFLAGS += -fno-omit-frame-pointer
> >  endif
> >
> > +# strchr is special case, as gcc might want to call its own strlen from there
> > +KBUILD_CFLAGS += -fno-builtin-strlen -fno-builtin-strcmp -fno-builtin-strncmp -fno-builtin-strchr
>
> I was poking around Ard's comment on that -DRISCV_EFI to try and figure
> out what it was doing, but I think this is the bigger issue.  I haven't
> benchmarked anything, but my guess is that turning off support for these
> builtin routines will outweigh the faster outline implementations of
> these routines.  I don't have any benchmarks to prove that, but in
> general compilers are pretty smart about handling these builtin routines
> in the common cases and deferring that to runtime is probably the wrong
> option.
>

Indeed. Case in point:

riscv64-linux-gnugcc -O -S -o - -xc - <<<"int foo() { return strlen(\"bar\"); }"

gives me

li a0,3
ret

whereas this

riscv64-linux-gnu-gcc -fno-builtin-strlen -O -S -o - -xc - <<<"int
foo() { return strlen(\"bar\"); }"

gives me

.LC0:
  .string "bar"
  .text
  .align 1
  .globl foo
  .type foo, @function
foo:
  addi sp,sp,-16
  sd ra,8(sp)
  lla a0,.LC0
  call strlen@plt
  ld ra,8(sp)
  addi sp,sp,16
  jr ra

Other str* and mem* routines are optimized in similar ways when
dealing with small sizes or compile time constants.

Also, I'd recommend avoiding redefining these prototypes to static
inline as it deviates from the official prototypes in the C library.

> I haven't looked all that closely at this patch set.  Is there some
> reason it's necessary to disable the builtin handling?  If not then my
> guess is it's better to leave that enabled unless some benchmarks show
> otherwise (and I don't know of any Zb* hardware to test against).
>

Why not have a single generic version of each in the binary with a
patchable NOP at the start, and patch that to an optimized version
when available? That way. all of the early code can remain as is.

Patch

diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 0d13b597cb55..581e4370c2a6 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -80,6 +80,9 @@  ifeq ($(CONFIG_PERF_EVENTS),y)
         KBUILD_CFLAGS += -fno-omit-frame-pointer
 endif
 
+# strchr is special case, as gcc might want to call its own strlen from there
+KBUILD_CFLAGS += -fno-builtin-strlen -fno-builtin-strcmp -fno-builtin-strncmp -fno-builtin-strchr
+
 KBUILD_CFLAGS_MODULE += $(call cc-option,-mno-relax)
 KBUILD_AFLAGS_MODULE += $(call as-option,-Wa$(comma)-mno-relax)
 
diff --git a/arch/riscv/include/asm/string.h b/arch/riscv/include/asm/string.h
index 909049366555..b98481d2d154 100644
--- a/arch/riscv/include/asm/string.h
+++ b/arch/riscv/include/asm/string.h
@@ -18,6 +18,72 @@  extern asmlinkage void *__memcpy(void *, const void *, size_t);
 #define __HAVE_ARCH_MEMMOVE
 extern asmlinkage void *memmove(void *, const void *, size_t);
 extern asmlinkage void *__memmove(void *, const void *, size_t);
+
+#define __HAVE_ARCH_STRCMP
+extern asmlinkage int __strcmp_generic(const char *cs, const char *ct);
+
+static inline int strcmp(const char *cs, const char *ct)
+{
+#ifdef RISCV_EFISTUB
+	return __strcmp_generic(cs, ct);
+#else
+	register const char *a0 asm("a0") = cs;
+	register const char *a1 asm("a1") = ct;
+	register int a0_out asm("a0");
+
+	asm volatile("call __strcmp_generic\n\t"
+		: "=r"(a0_out)
+		: "r"(a0), "r"(a1)
+		: "ra", "t0", "t1", "t2");
+
+	return a0_out;
+#endif
+}
+
+#define __HAVE_ARCH_STRNCMP
+extern asmlinkage int __strncmp_generic(const char *cs,
+					const char *ct, size_t count);
+
+static inline int strncmp(const char *cs, const char *ct, size_t count)
+{
+#ifdef RISCV_EFISTUB
+	return __strncmp_generic(cs, ct, count);
+#else
+	register const char *a0 asm("a0") = cs;
+	register const char *a1 asm("a1") = ct;
+	register size_t a2 asm("a2") = count;
+	register int a0_out asm("a0");
+
+	asm volatile("call __strncmp_generic\n\t"
+		: "=r"(a0_out)
+		: "r"(a0), "r"(a1), "r"(a2)
+		: "ra", "t0", "t1", "t2");
+
+	return a0_out;
+#endif
+}
+
+#define __HAVE_ARCH_STRLEN
+extern asmlinkage __kernel_size_t __strlen_generic(const char *);
+
+static inline __kernel_size_t strlen(const char *s)
+{
+#ifdef RISCV_EFISTUB
+	return __strlen_generic(s);
+#else
+	register const char *a0 asm("a0") = s;
+	register int a0_out asm("a0");
+
+	asm volatile(
+		"call __strlen_generic\n\t"
+		: "=r"(a0_out)
+		: "r"(a0)
+		: "ra", "t0", "t1");
+
+	return a0_out;
+#endif
+}
+
 /* For those files which don't want to check by kasan. */
 #if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
 #define memcpy(dst, src, len) __memcpy(dst, src, len)
diff --git a/arch/riscv/kernel/image-vars.h b/arch/riscv/kernel/image-vars.h
index d6e5f739905e..2f270b9fde63 100644
--- a/arch/riscv/kernel/image-vars.h
+++ b/arch/riscv/kernel/image-vars.h
@@ -25,10 +25,10 @@ 
  */
 __efistub_memcmp		= memcmp;
 __efistub_memchr		= memchr;
-__efistub_strlen		= strlen;
+__efistub___strlen_generic	= __strlen_generic;
 __efistub_strnlen		= strnlen;
-__efistub_strcmp		= strcmp;
-__efistub_strncmp		= strncmp;
+__efistub___strcmp_generic	= __strcmp_generic;
+__efistub___strncmp_generic	= __strncmp_generic;
 __efistub_strrchr		= strrchr;
 
 __efistub__start		= _start;
diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
index 25d5c9664e57..6c74b0bedd60 100644
--- a/arch/riscv/lib/Makefile
+++ b/arch/riscv/lib/Makefile
@@ -3,6 +3,9 @@  lib-y			+= delay.o
 lib-y			+= memcpy.o
 lib-y			+= memset.o
 lib-y			+= memmove.o
+lib-y			+= strcmp.o
+lib-y			+= strlen.o
+lib-y			+= strncmp.o
 lib-$(CONFIG_MMU)	+= uaccess.o
 lib-$(CONFIG_64BIT)	+= tishift.o
 
diff --git a/arch/riscv/lib/strcmp.S b/arch/riscv/lib/strcmp.S
new file mode 100644
index 000000000000..f4b7f4e806f0
--- /dev/null
+++ b/arch/riscv/lib/strcmp.S
@@ -0,0 +1,38 @@ 
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <linux/linkage.h>
+#include <asm/asm.h>
+#include <asm-generic/export.h>
+
+/* int __strcmp_generic(const char *cs, const char *ct) */
+ENTRY(__strcmp_generic)
+	/*
+	 * Returns
+	 *   a0 - comparison result, value like strcmp
+	 *
+	 * Parameters
+	 *   a0 - string1
+	 *   a1 - string2
+	 *
+	 * Clobbers
+	 *   t0, t1, t2
+	 */
+	mv	t2, a1
+1:
+	lbu	t1, 0(a0)
+	lbu	t0, 0(a1)
+	addi	a0, a0, 1
+	addi	a1, a1, 1
+	beq	t1, t0, 3f
+	li	a0, 1
+	bgeu	t1, t0, 2f
+	li	a0, -1
+2:
+	mv	a1, t2
+	ret
+3:
+	bnez	t1, 1b
+	li	a0, 0
+	j	2b
+END(__strcmp_generic)
+EXPORT_SYMBOL(__strcmp_generic)
diff --git a/arch/riscv/lib/strlen.S b/arch/riscv/lib/strlen.S
new file mode 100644
index 000000000000..e0e7440ac724
--- /dev/null
+++ b/arch/riscv/lib/strlen.S
@@ -0,0 +1,29 @@ 
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <linux/linkage.h>
+#include <asm/asm.h>
+#include <asm-generic/export.h>
+
+/* int __strlen_generic(const char *s) */
+ENTRY(__strlen_generic)
+	/*
+	 * Returns
+	 *   a0 - string length
+	 *
+	 * Parameters
+	 *   a0 - String to measure
+	 *
+	 * Clobbers:
+	 *   t0, t1
+	 */
+	mv	t1, a0
+1:
+	lbu	t0, 0(t1)
+	bnez	t0, 2f
+	sub	a0, t1, a0
+	ret
+2:
+	addi	t1, t1, 1
+	j	1b
+END(__strlen_generic)
+EXPORT_SYMBOL(__strlen_generic)
diff --git a/arch/riscv/lib/strncmp.S b/arch/riscv/lib/strncmp.S
new file mode 100644
index 000000000000..7e116d942265
--- /dev/null
+++ b/arch/riscv/lib/strncmp.S
@@ -0,0 +1,41 @@ 
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <linux/linkage.h>
+#include <asm/asm.h>
+#include <asm-generic/export.h>
+
+/* int __strncmp_generic(const char *cs, const char *ct, size_t count) */
+ENTRY(__strncmp_generic)
+	/*
+	 * Returns
+	 *   a0 - comparison result, value like strncmp
+	 *
+	 * Parameters
+	 *   a0 - string1
+	 *   a1 - string2
+	 *   a2 - number of characters to compare
+	 *
+	 * Clobbers
+	 *   t0, t1, t2
+	 */
+	li	t0, 0
+1:
+	beq	a2, t0, 4f
+	add	t1, a0, t0
+	add	t2, a1, t0
+	lbu	t1, 0(t1)
+	lbu	t2, 0(t2)
+	beq	t1, t2, 3f
+	li	a0, 1
+	bgeu	t1, t2, 2f
+	li	a0, -1
+2:
+	ret
+3:
+	addi	t0, t0, 1
+	bnez	t1, 1b
+4:
+	li	a0, 0
+	j	2b
+END(__strncmp_generic)
+EXPORT_SYMBOL(__strncmp_generic)