arm64/lib: Handle CRC-32 alternative in C code

In preparation for adding another code path for performing CRC-32, move
the alternative patching for ARM64_HAS_CRC32 into C code. The logic for
deciding whether to use this new code path will be implemented in C too.

Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20241018075347.2821102-6-ardb+git@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: ardbiesheuvel

arch/arm64/lib/Makefile

@@ -13,7 +13,7 @@ endif
 
 lib-$(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) += uaccess_flushcache.o
 
-obj-$(CONFIG_CRC32) += crc32.o
+obj-$(CONFIG_CRC32) += crc32.o crc32-glue.o
 
 obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
 

arch/arm64/lib/crc32-glue.c

@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/crc32.h>
+#include <linux/linkage.h>
+
+#include <asm/alternative.h>
+
+asmlinkage u32 crc32_le_arm64(u32 crc, unsigned char const *p, size_t len);
+asmlinkage u32 crc32c_le_arm64(u32 crc, unsigned char const *p, size_t len);
+asmlinkage u32 crc32_be_arm64(u32 crc, unsigned char const *p, size_t len);
+
+u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
+{
+	if (!alternative_has_cap_likely(ARM64_HAS_CRC32))
+		return crc32_le_base(crc, p, len);
+
+	return crc32_le_arm64(crc, p, len);
+}
+
+u32 __pure __crc32c_le(u32 crc, unsigned char const *p, size_t len)
+{
+	if (!alternative_has_cap_likely(ARM64_HAS_CRC32))
+		return __crc32c_le_base(crc, p, len);
+
+	return crc32c_le_arm64(crc, p, len);
+}
+
+u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
+{
+	if (!alternative_has_cap_likely(ARM64_HAS_CRC32))
+		return crc32_be_base(crc, p, len);
+
+	return crc32_be_arm64(crc, p, len);
+}

arch/arm64/lib/crc32.S

@@ -6,7 +6,6 @@
  */
 
 #include <linux/linkage.h>
-#include <asm/alternative.h>
 #include <asm/assembler.h>
 
 	.arch		armv8-a+crc
@@ -136,25 +135,16 @@ CPU_BE( rev16		\reg, \reg	)
 	.endm
 
 	.align		5
-SYM_FUNC_START(crc32_le)
-alternative_if_not ARM64_HAS_CRC32
-	b		crc32_le_base
-alternative_else_nop_endif
+SYM_FUNC_START(crc32_le_arm64)
 	__crc32
-SYM_FUNC_END(crc32_le)
+SYM_FUNC_END(crc32_le_arm64)
 
 	.align		5
-SYM_FUNC_START(__crc32c_le)
-alternative_if_not ARM64_HAS_CRC32
-	b		__crc32c_le_base
-alternative_else_nop_endif
+SYM_FUNC_START(crc32c_le_arm64)
 	__crc32		c
-SYM_FUNC_END(__crc32c_le)
+SYM_FUNC_END(crc32c_le_arm64)
 
 	.align		5
-SYM_FUNC_START(crc32_be)
-alternative_if_not ARM64_HAS_CRC32
-	b		crc32_be_base
-alternative_else_nop_endif
+SYM_FUNC_START(crc32_be_arm64)
 	__crc32		be=1
-SYM_FUNC_END(crc32_be)
+SYM_FUNC_END(crc32_be_arm64)