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>

1 files changed, 28 insertions, 7 deletions

diff --git a/include/linux/crc32.h b/include/linux/crc32.h
index 5b07fc9081c4..58c632533b08 100644
--- a/include/linux/crc32.h
+++ b/include/linux/crc32.h
@@ -8,10 +8,34 @@
 #include <linux/types.h>
 #include <linux/bitrev.h>
 
-u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len);
-u32 __pure crc32_le_base(u32 crc, unsigned char const *p, size_t len);
-u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len);
-u32 __pure crc32_be_base(u32 crc, unsigned char const *p, size_t len);
+u32 __pure crc32_le_arch(u32 crc, const u8 *p, size_t len);
+u32 __pure crc32_le_base(u32 crc, const u8 *p, size_t len);
+u32 __pure crc32_be_arch(u32 crc, const u8 *p, size_t len);
+u32 __pure crc32_be_base(u32 crc, const u8 *p, size_t len);
+u32 __pure crc32c_le_arch(u32 crc, const u8 *p, size_t len);
+u32 __pure crc32c_le_base(u32 crc, const u8 *p, size_t len);
+
+static inline u32 __pure crc32_le(u32 crc, const u8 *p, size_t len)
+{
+	if (IS_ENABLED(CONFIG_CRC32_ARCH))
+		return crc32_le_arch(crc, p, len);
+	return crc32_le_base(crc, p, len);
+}
+
+static inline u32 __pure crc32_be(u32 crc, const u8 *p, size_t len)
+{
+	if (IS_ENABLED(CONFIG_CRC32_ARCH))
+		return crc32_be_arch(crc, p, len);
+	return crc32_be_base(crc, p, len);
+}
+
+/* TODO: leading underscores should be dropped once callers have been updated */
+static inline u32 __pure __crc32c_le(u32 crc, const u8 *p, size_t len)
+{
+	if (IS_ENABLED(CONFIG_CRC32_ARCH))
+		return crc32c_le_arch(crc, p, len);
+	return crc32c_le_base(crc, p, len);
+}
 
 /**
  * crc32_le_combine - Combine two crc32 check values into one. For two
@@ -38,9 +62,6 @@ static inline u32 crc32_le_combine(u32 crc1, u32 crc2, size_t len2)
 	return crc32_le_shift(crc1, len2) ^ crc2;
 }
 
-u32 __pure __crc32c_le(u32 crc, unsigned char const *p, size_t len);
-u32 __pure crc32c_le_base(u32 crc, unsigned char const *p, size_t len);
-
 /**
  * __crc32c_le_combine - Combine two crc32c check values into one. For two
  * 			 sequences of bytes, seq1 and seq2 with lengths len1