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

Andrew Jones
2022-12-01T20:11:05Z

On Wed, Nov 30, 2022 at 11:56:13PM +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.

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 <conor.dooley@microchip.com>
> Signed-off-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
> ---
> 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 <ajones@ventanamicro.com>

Thanks,
drew