lib/crc32: improve support for arch-specific overrides

Currently the CRC32 library functions are defined as weak symbols, and
the arm64 and riscv architectures override them.

This method of arch-specific overrides has the limitation that it only
works when both the base and arch code is built-in.  Also, it makes the
arch-specific code be silently not used if it is accidentally built with
lib-y instead of obj-y; unfortunately the RISC-V code does this.

This commit reorganizes the code to have explicit *_arch() functions
that are called when they are enabled, similar to how some of the crypto
library code works (e.g. chacha_crypt() calls chacha_crypt_arch()).

Make the existing kconfig choice for the CRC32 implementation also
control whether the arch-optimized implementation (if one is available)
is enabled or not.  Make it enabled by default if CRC32 is also enabled.

The result is that arch-optimized CRC32 library functions will be
included automatically when appropriate, but it is now possible to
disable them.  They can also now be built as a loadable module if the
CRC32 library functions happen to be used only by loadable modules, in
which case the arch and base CRC32 modules will be automatically loaded
via direct symbol dependency when appropriate.

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20241202010844.144356-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>

3 files changed, 13 insertions, 4 deletions

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 100570a048c5..71f6310c8240 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -21,6 +21,7 @@ config ARM64
 	select ARCH_ENABLE_THP_MIGRATION if TRANSPARENT_HUGEPAGE
 	select ARCH_HAS_CACHE_LINE_SIZE
 	select ARCH_HAS_CC_PLATFORM
+	select ARCH_HAS_CRC32
 	select ARCH_HAS_CURRENT_STACK_POINTER
 	select ARCH_HAS_DEBUG_VIRTUAL
 	select ARCH_HAS_DEBUG_VM_PGTABLE
diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile
index 8e882f479d98..5fbcf0d56665 100644
--- a/arch/arm64/lib/Makefile
+++ b/arch/arm64/lib/Makefile
@@ -13,7 +13,8 @@ endif
 
 lib-$(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) += uaccess_flushcache.o
 
-obj-$(CONFIG_CRC32) += crc32.o crc32-glue.o
+obj-$(CONFIG_CRC32_ARCH) += crc32-arm64.o
+crc32-arm64-y := crc32.o crc32-glue.o
 
 obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
 
diff --git a/arch/arm64/lib/crc32-glue.c b/arch/arm64/lib/crc32-glue.c
index ad015223d15d..d7f6e1cbf0d2 100644
--- a/arch/arm64/lib/crc32-glue.c
+++ b/arch/arm64/lib/crc32-glue.c
@@ -2,6 +2,7 @@
 
 #include <linux/crc32.h>
 #include <linux/linkage.h>
+#include <linux/module.h>
 
 #include <asm/alternative.h>
 #include <asm/cpufeature.h>
@@ -21,7 +22,7 @@ asmlinkage u32 crc32_le_arm64_4way(u32 crc, unsigned char const *p, size_t len);
 asmlinkage u32 crc32c_le_arm64_4way(u32 crc, unsigned char const *p, size_t len);
 asmlinkage u32 crc32_be_arm64_4way(u32 crc, unsigned char const *p, size_t len);
 
-u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
+u32 __pure crc32_le_arch(u32 crc, const u8 *p, size_t len)
 {
 	if (!alternative_has_cap_likely(ARM64_HAS_CRC32))
 		return crc32_le_base(crc, p, len);
@@ -40,8 +41,9 @@ u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
 
 	return crc32_le_arm64(crc, p, len);
 }
+EXPORT_SYMBOL(crc32_le_arch);
 
-u32 __pure __crc32c_le(u32 crc, unsigned char const *p, size_t len)
+u32 __pure crc32c_le_arch(u32 crc, const u8 *p, size_t len)
 {
 	if (!alternative_has_cap_likely(ARM64_HAS_CRC32))
 		return crc32c_le_base(crc, p, len);
@@ -60,8 +62,9 @@ u32 __pure __crc32c_le(u32 crc, unsigned char const *p, size_t len)
 
 	return crc32c_le_arm64(crc, p, len);
 }
+EXPORT_SYMBOL(crc32c_le_arch);
 
-u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
+u32 __pure crc32_be_arch(u32 crc, const u8 *p, size_t len)
 {
 	if (!alternative_has_cap_likely(ARM64_HAS_CRC32))
 		return crc32_be_base(crc, p, len);
@@ -80,3 +83,7 @@ u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
 
 	return crc32_be_arm64(crc, p, len);
 }
+EXPORT_SYMBOL(crc32_be_arch);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("arm64-optimized CRC32 functions");