[PATCH RFC 7/9] RISC-V: add infrastructure to allow different str* implementations
Heiko Stuebner
heiko at sntech.de
Fri Nov 4 15:51:51 PDT 2022
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 at sntech.de>
---
arch/riscv/include/asm/string.h | 77 +++++++++++++++++++++++++++++++++
arch/riscv/kernel/image-vars.h | 6 +--
arch/riscv/lib/Makefile | 4 ++
arch/riscv/lib/strcmp.S | 25 +++++++++++
arch/riscv/lib/string.c | 20 +++++++++
arch/riscv/lib/strlen.S | 17 ++++++++
arch/riscv/lib/strncmp.S | 27 ++++++++++++
7 files changed, 173 insertions(+), 3 deletions(-)
create mode 100644 arch/riscv/lib/strcmp.S
create mode 100644 arch/riscv/lib/string.c
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..41eef000d18f 100644
--- a/arch/riscv/include/asm/string.h
+++ b/arch/riscv/include/asm/string.h
@@ -18,6 +18,83 @@ 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 __always_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);
+extern asmlinkage int __strncmp_zbb(const char *cs,
+ const char *ct, size_t count);
+
+static __always_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 __always_inline __kernel_size_t strlen(const char *s)
+{
+ 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;
+}
+
+#define __HAVE_ARCH_STRSTARTS
+static inline bool strstarts(const char *str, const char *prefix)
+{
+#ifdef RISCV_EFISTUB
+ return __strncmp_generic(str, prefix, __strlen_generic(prefix)) == 0;
+#else
+ return strncmp(str, prefix, strlen(prefix)) == 0;
+#endif
+}
+
+#define __HAVE_ARCH_STRCHR
+char *strchr(const char *s, int c);
+
/* 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..38a18ce9acef 100644
--- a/arch/riscv/lib/Makefile
+++ b/arch/riscv/lib/Makefile
@@ -3,6 +3,10 @@ lib-y += delay.o
lib-y += memcpy.o
lib-y += memset.o
lib-y += memmove.o
+lib-y += string.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..c74742699cd5
--- /dev/null
+++ b/arch/riscv/lib/strcmp.S
@@ -0,0 +1,25 @@
+#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)
+ 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/string.c b/arch/riscv/lib/string.c
new file mode 100644
index 000000000000..b595c95d0f23
--- /dev/null
+++ b/arch/riscv/lib/string.c
@@ -0,0 +1,20 @@
+#include <linux/export.h>
+#include <linux/types.h>
+#include <linux/printk.h>
+
+/**
+ * strchr - Find the first occurrence of a character in a string
+ * @s: The string to be searched
+ * @c: The character to search for
+ *
+ * Note that the %NUL-terminator is considered part of the string, and can
+ * be searched for.
+ */
+char *strchr(const char *s, int c)
+{
+ for (; *s != (char)c; ++s)
+ if (*s == '\0')
+ return NULL;
+ return (char *)s;
+}
+EXPORT_SYMBOL(strchr);
diff --git a/arch/riscv/lib/strlen.S b/arch/riscv/lib/strlen.S
new file mode 100644
index 000000000000..ed27b933ddcb
--- /dev/null
+++ b/arch/riscv/lib/strlen.S
@@ -0,0 +1,17 @@
+#include <linux/linkage.h>
+#include <asm/asm.h>
+#include <asm-generic/export.h>
+
+/* int __strlen_generic(const char *s) */
+ENTRY(__strlen_generic)
+ 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..9dbb85490127
--- /dev/null
+++ b/arch/riscv/lib/strncmp.S
@@ -0,0 +1,27 @@
+#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)
+ 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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