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

Andrew Jones
2022-12-01T20:19:07Z

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 <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");

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 <ajones@ventanamicro.com>
>
> Thanks,
> drew