lib/crc32: make core crc32() routines weak so they can be overridden

mainline inclusion
from mainline-4.20-rc1
commit: 9784d82db3eb3de7851e5a3f4a2481607de2452c
category: feature
feature: accelerated crc32 routines
bugzilla: 13702
CVE: NA

--------------------------------------------------

Allow architectures to drop in accelerated CRC32 routines by making
the crc32_le/__crc32c_le entry points weak, and exposing non-weak
aliases for them that may be used by the accelerated versions as
fallbacks in case the instructions they rely upon are not available.
Acked-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NHanjun Guo <guohanjun@huawei.com>
Signed-off-by: NXie XiuQi <xiexiuqi@huawei.com>
Reviewed-by: NHanjun Guo <guohanjun@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

lib/crc32.c

@@ -183,21 +183,21 @@ static inline u32 __pure crc32_le_generic(u32 crc, unsigned char const *p,
 }
 
 #if CRC_LE_BITS == 1
-u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
+u32 __pure __weak crc32_le(u32 crc, unsigned char const *p, size_t len)
 {
 	return crc32_le_generic(crc, p, len, NULL, CRC32_POLY_LE);
 }
-u32 __pure __crc32c_le(u32 crc, unsigned char const *p, size_t len)
+u32 __pure __weak __crc32c_le(u32 crc, unsigned char const *p, size_t len)
 {
 	return crc32_le_generic(crc, p, len, NULL, CRC32C_POLY_LE);
 }
 #else
-u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
+u32 __pure __weak crc32_le(u32 crc, unsigned char const *p, size_t len)
 {
 	return crc32_le_generic(crc, p, len,
 			(const u32 (*)[256])crc32table_le, CRC32_POLY_LE);
 }
-u32 __pure __crc32c_le(u32 crc, unsigned char const *p, size_t len)
+u32 __pure __weak __crc32c_le(u32 crc, unsigned char const *p, size_t len)
 {
 	return crc32_le_generic(crc, p, len,
 			(const u32 (*)[256])crc32ctable_le, CRC32C_POLY_LE);
@@ -206,6 +206,9 @@ u32 __pure __crc32c_le(u32 crc, unsigned char const *p, size_t len)
 EXPORT_SYMBOL(crc32_le);
 EXPORT_SYMBOL(__crc32c_le);
 
+u32 crc32_le_base(u32, unsigned char const *, size_t) __alias(crc32_le);
+u32 __crc32c_le_base(u32, unsigned char const *, size_t) __alias(__crc32c_le);
+
 /*
  * This multiplies the polynomials x and y modulo the given modulus.
  * This follows the "little-endian" CRC convention that the lsbit