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

[Heiko Stuebner <heiko@sntech.de>]

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
+	 *
+	 * Parameters
+	 *   a0 - string1
+	 *   a1 - string2
+	 *   a2 - number of characters to compare
+	 *
+	 * Clobbers
+	 *   t0, t1, t2, t3, t4, t5
+	 */
+	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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