Unverified Commit 56e0790c authored by Heiko Stuebner's avatar Heiko Stuebner Committed by Palmer Dabbelt
Browse files

RISC-V: add infrastructure to allow different str* implementations 



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 Linux kernel provides standard implementations for string functions
but when architectures want to extend them, they need to provide their
own.

The added generic string functions are done in assembler (taken from
disassembling the main-kernel functions for now) to allow us to control
the used registers and extend them with optimized variants.

This doesn't override the compiler's use of builtin replacements. So still
first of all the compiler will select if a builtin will be better suitable
i.e. for known strings. For all regular cases we will want to later
select possible optimized variants and in the worst case fall back to the
generic implemention added with this change.

Reviewed-by: default avatarAndrew Jones <ajones@ventanamicro.com>
Signed-off-by: default avatarHeiko Stuebner <heiko.stuebner@vrull.eu>
Reviewed-by: default avatarConor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230113212301.3534711-2-heiko@sntech.de


Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent 61a9b712

arch/riscv/include/asm/string.h

+10 −0
Original line number Diff line number Diff line
@@ -18,6 +18,16 @@ 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(const char *cs, const char *ct);



#define __HAVE_ARCH_STRLEN

extern asmlinkage __kernel_size_t strlen(const char *);



#define __HAVE_ARCH_STRNCMP

extern asmlinkage int strncmp(const char *cs, const char *ct, size_t count);



/* 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)

arch/riscv/kernel/riscv_ksyms.c

+3 −0
Original line number Diff line number Diff line
@@ -12,6 +12,9 @@ 
EXPORT_SYMBOL(memset);

EXPORT_SYMBOL(memcpy);

EXPORT_SYMBOL(memmove);

EXPORT_SYMBOL(strcmp);

EXPORT_SYMBOL(strlen);

EXPORT_SYMBOL(strncmp);

EXPORT_SYMBOL(__memset);

EXPORT_SYMBOL(__memcpy);

EXPORT_SYMBOL(__memmove);

arch/riscv/lib/Makefile

+3 −0
Original line number Diff line number Diff line
@@ -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

arch/riscv/lib/strcmp.S

0 → 100644
+36 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0-only */



#include <linux/linkage.h>

#include <asm/asm.h>

#include <asm-generic/export.h>



/* int strcmp(const char *cs, const char *ct) */

SYM_FUNC_START(strcmp)

	/*

	 * Returns

	 *   a0 - comparison result, value like strcmp

	 *

	 * Parameters

	 *   a0 - string1

	 *   a1 - string2

	 *

	 * Clobbers

	 *   t0, t1

	 */

1:

	lbu	t0, 0(a0)

	lbu	t1, 0(a1)

	addi	a0, a0, 1

	addi	a1, a1, 1

	bne	t0, t1, 2f

	bnez	t0, 1b

	li	a0, 0

	ret

2:

	/*

	 * strcmp only needs to return (< 0, 0, > 0) values

	 * not necessarily -1, 0, +1

	 */

	sub	a0, t0, t1

	ret

SYM_FUNC_END(strcmp)

arch/riscv/lib/strlen.S

0 → 100644
+28 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0-only */



#include <linux/linkage.h>

#include <asm/asm.h>

#include <asm-generic/export.h>



/* int strlen(const char *s) */

SYM_FUNC_START(strlen)

	/*

	 * Returns

	 *   a0 - string length

	 *

	 * Parameters

	 *   a0 - String to measure

	 *

	 * Clobbers:

	 *   t0, t1

	 */

	mv	t1, a0

1:

	lbu	t0, 0(t1)

	beqz	t0, 2f

	addi	t1, t1, 1

	j	1b

2:

	sub	a0, t1, a0

	ret

SYM_FUNC_END(strlen)