[PATCH v5 1/2] RISC-V: add infrastructure to allow different str* implementations
Heiko Stuebner
heiko at sntech.de
Fri Jan 13 13:23:00 PST 2023
From: Heiko Stuebner <heiko.stuebner at 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.
This doesn't override the compiler's use of builtin replacements. So still
first of all the compiler will select if a builtin will be better suitable
i.e. for known strings. For all regular cases we will want to later
select possible optimized variants and in the worst case fall back to the
generic implemention added with this change.
Reviewed-by: Andrew Jones <ajones at ventanamicro.com>
Signed-off-by: Heiko Stuebner <heiko.stuebner at vrull.eu>
---
arch/riscv/include/asm/string.h | 10 ++++++++
arch/riscv/kernel/riscv_ksyms.c | 3 +++
arch/riscv/lib/Makefile | 3 +++
arch/riscv/lib/strcmp.S | 36 +++++++++++++++++++++++++++++
arch/riscv/lib/strlen.S | 28 ++++++++++++++++++++++
arch/riscv/lib/strncmp.S | 41 +++++++++++++++++++++++++++++++++
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..8babd712b958
--- /dev/null
+++ b/arch/riscv/lib/strcmp.S
@@ -0,0 +1,36 @@
+/* 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
+ */
+1:
+ lbu t0, 0(a0)
+ lbu t1, 0(a1)
+ addi a0, a0, 1
+ addi a1, a1, 1
+ bne t0, t1, 2f
+ bnez t0, 1b
+ li a0, 0
+ ret
+2:
+ /*
+ * strcmp only needs to return (< 0, 0, > 0) values
+ * not necessarily -1, 0, +1
+ */
+ sub a0, t0, t1
+ ret
+SYM_FUNC_END(strcmp)
diff --git a/arch/riscv/lib/strlen.S b/arch/riscv/lib/strlen.S
new file mode 100644
index 000000000000..0a3b11853efd
--- /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)
+ beqz t0, 2f
+ addi t1, t1, 1
+ j 1b
+2:
+ sub a0, t1, a0
+ ret
+SYM_FUNC_END(strlen)
diff --git a/arch/riscv/lib/strncmp.S b/arch/riscv/lib/strncmp.S
new file mode 100644
index 000000000000..1f644d0a93f6
--- /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(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 t2, 0
+1:
+ beq a2, t2, 2f
+ lbu t0, 0(a0)
+ lbu t1, 0(a1)
+ addi a0, a0, 1
+ addi a1, a1, 1
+ bne t0, t1, 3f
+ addi t2, t2, 1
+ bnez t0, 1b
+2:
+ li a0, 0
+ ret
+3:
+ /*
+ * strncmp only needs to return (< 0, 0, > 0) values
+ * not necessarily -1, 0, +1
+ */
+ sub a0, t0, t1
+ ret
+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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