Re: [PATCH 6/7] RISC-V: add infrastructure to allow different str* implementations

[Conor Dooley <conor@kernel.org>]

On Thu, Nov 10, 2022 at 05:49:23PM +0100, Heiko Stuebner wrote:
> From: Heiko Stuebner <heiko.stuebner@vrull.eu>
> 
> 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.
> 
> Signed-off-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
> ---
>  arch/riscv/include/asm/string.h | 66 +++++++++++++++++++++++++++++++++
>  arch/riscv/kernel/image-vars.h  |  6 +--
>  arch/riscv/lib/Makefile         |  3 ++
>  arch/riscv/lib/strcmp.S         | 39 +++++++++++++++++++
>  arch/riscv/lib/strlen.S         | 29 +++++++++++++++
>  arch/riscv/lib/strncmp.S        | 41 ++++++++++++++++++++
>  6 files changed, 181 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/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..f23a5c5e39d8
> --- /dev/null
> +++ b/arch/riscv/lib/strcmp.S
> @@ -0,0 +1,39 @@
> +/* 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, like strncmp

The strncmp_generic one below says "like strncmp" too. Given the below
copy paste stuff, is this one copy paste or intentional?

> +	 *
> +	 * Parameters
> +	 *   a0 - string1
> +	 *   a1 - string2
> +	 *   a2 - number of characters to compare

Above line is a copy paste error?

> +	 *
> +	 * Clobbers
> +	 *   t0, t1, t2, t3, t4, t5

As is this one?

Other than those, seems to make sense?

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

> +	 */
> +	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..8d271cd0df72
> --- /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, 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
> 
> 
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