Re: [PATCH v4 4/5] RISC-V: add infrastructure to allow different str* implementations

[Conor Dooley <conor@kernel.org>]

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On Mon, Jan 09, 2023 at 07:17:54PM +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 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.
> 
> Signed-off-by: Heiko Stuebner <heiko.stuebner@vrull.eu>

asm looks the same as what I previously provided a review for, but I
assume you dropped cos of the EFI stub stuff? You can have it back I
suppose..
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

> ---
>  arch/riscv/include/asm/string.h | 10 +++++++++
>  arch/riscv/kernel/riscv_ksyms.c |  3 +++
>  arch/riscv/lib/Makefile         |  3 +++
>  arch/riscv/lib/strcmp.S         | 37 ++++++++++++++++++++++++++++++
>  arch/riscv/lib/strlen.S         | 28 +++++++++++++++++++++++
>  arch/riscv/lib/strncmp.S        | 40 +++++++++++++++++++++++++++++++++
>  arch/riscv/purgatory/Makefile   | 13 +++++++++++
>  7 files changed, 134 insertions(+)
>  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..a96b1fea24fe 100644
> --- a/arch/riscv/include/asm/string.h
> +++ b/arch/riscv/include/asm/string.h
> @@ -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)
> diff --git a/arch/riscv/kernel/riscv_ksyms.c b/arch/riscv/kernel/riscv_ksyms.c
> index 5ab1c7e1a6ed..a72879b4249a 100644
> --- a/arch/riscv/kernel/riscv_ksyms.c
> +++ b/arch/riscv/kernel/riscv_ksyms.c
> @@ -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);
> 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..94440fb8390c
> --- /dev/null
> +++ b/arch/riscv/lib/strcmp.S
> @@ -0,0 +1,37 @@
> +/* 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, 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
> +SYM_FUNC_END(strcmp)
> diff --git a/arch/riscv/lib/strlen.S b/arch/riscv/lib/strlen.S
> new file mode 100644
> index 000000000000..09a7aaff26c8
> --- /dev/null
> +++ b/arch/riscv/lib/strlen.S
> @@ -0,0 +1,28 @@
> +/* 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)
> +	bnez	t0, 2f
> +	sub	a0, t1, a0
> +	ret
> +2:
> +	addi	t1, t1, 1
> +	j	1b
> +SYM_FUNC_END(strlen)
> diff --git a/arch/riscv/lib/strncmp.S b/arch/riscv/lib/strncmp.S
> new file mode 100644
> index 000000000000..493ab6febcb2
> --- /dev/null
> +++ b/arch/riscv/lib/strncmp.S
> @@ -0,0 +1,40 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#include <linux/linkage.h>
> +#include <asm/asm.h>
> +#include <asm-generic/export.h>
> +
> +/* int strncmp(const char *cs, const char *ct, size_t count) */
> +SYM_FUNC_START(strncmp)
> +	/*
> +	 * 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
> +SYM_FUNC_END(strncmp)
> diff --git a/arch/riscv/purgatory/Makefile b/arch/riscv/purgatory/Makefile
> index dd58e1d99397..d16bf715a586 100644
> --- a/arch/riscv/purgatory/Makefile
> +++ b/arch/riscv/purgatory/Makefile
> @@ -2,6 +2,7 @@
>  OBJECT_FILES_NON_STANDARD := y
>  
>  purgatory-y := purgatory.o sha256.o entry.o string.o ctype.o memcpy.o memset.o
> +purgatory-y += strcmp.o strlen.o strncmp.o
>  
>  targets += $(purgatory-y)
>  PURGATORY_OBJS = $(addprefix $(obj)/,$(purgatory-y))
> @@ -18,6 +19,15 @@ $(obj)/memcpy.o: $(srctree)/arch/riscv/lib/memcpy.S FORCE
>  $(obj)/memset.o: $(srctree)/arch/riscv/lib/memset.S FORCE
>  	$(call if_changed_rule,as_o_S)
>  
> +$(obj)/strcmp.o: $(srctree)/arch/riscv/lib/strcmp.S FORCE
> +	$(call if_changed_rule,as_o_S)
> +
> +$(obj)/strlen.o: $(srctree)/arch/riscv/lib/strlen.S FORCE
> +	$(call if_changed_rule,as_o_S)
> +
> +$(obj)/strncmp.o: $(srctree)/arch/riscv/lib/strncmp.S FORCE
> +	$(call if_changed_rule,as_o_S)
> +
>  $(obj)/sha256.o: $(srctree)/lib/crypto/sha256.c FORCE
>  	$(call if_changed_rule,cc_o_c)
>  
> @@ -77,6 +87,9 @@ CFLAGS_ctype.o			+= $(PURGATORY_CFLAGS)
>  AFLAGS_REMOVE_entry.o		+= -Wa,-gdwarf-2
>  AFLAGS_REMOVE_memcpy.o		+= -Wa,-gdwarf-2
>  AFLAGS_REMOVE_memset.o		+= -Wa,-gdwarf-2
> +AFLAGS_REMOVE_strcmp.o		+= -Wa,-gdwarf-2
> +AFLAGS_REMOVE_strlen.o		+= -Wa,-gdwarf-2
> +AFLAGS_REMOVE_strncmp.o		+= -Wa,-gdwarf-2
>  
>  $(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE
>  		$(call if_changed,ld)
> -- 
> 2.35.1
> 

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