[PATCH] x86/boot/compressed: Use builtin mem functions for decompressor

From: Arvind Sankar
Date: Mon Aug 03 2020 - 17:07:37 EST

Since commits

c041b5ad8640 ("x86, boot: Create a separate string.h file to provide standard string functions")
fb4cac573ef6 ("x86, boot: Move memcmp() into string.h and string.c")

the decompressor stub has been using the compiler's builtin memcpy,
memset and memcmp functions, _except_ where it would likely have the
largest impact, in the decompression code itself.

Remove the #undef's of memcpy and memset in misc.c so that the
decompressor code also uses the compiler builtins.

The rationale given in the comment doesn't really apply: just because
some functions use the out-of-line version is no reason to not use the
builtin version in the rest.

Replace the comment with an explanation of why memzero and memmove are
being #define'd.

Drop the suggestion to #undef in boot/string.h as well: the out-of-line
versions are not really optimized versions, they're generic code that's
good enough for the preboot environment. The compiler will likely
generate better code for constant-size memcpy/memset/memcmp if it is
allowed to.

Signed-off-by: Arvind Sankar <nivedita@xxxxxxxxxxxx>
arch/x86/boot/compressed/misc.c | 7 ++-----
arch/x86/boot/string.h | 5 +----
2 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index 9652d5c2afda..0c74a6e526b6 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -30,12 +30,9 @@
#define STATIC static

- * Use normal definitions of mem*() from string.c. There are already
- * included header files which expect a definition of memset() and by
- * the time we define memset macro, it is too late.
+ * Provide definitions of memzero and memmove as some of the decompressors will
+ * try to define their own functions if these are not defined as macros.
-#undef memcpy
-#undef memset
#define memzero(s, n) memset((s), 0, (n))
#define memmove memmove

diff --git a/arch/x86/boot/string.h b/arch/x86/boot/string.h
index 995f7b7ad512..a232da487cd2 100644
--- a/arch/x86/boot/string.h
+++ b/arch/x86/boot/string.h
@@ -11,10 +11,7 @@ void *memcpy(void *dst, const void *src, size_t len);
void *memset(void *dst, int c, size_t len);
int memcmp(const void *s1, const void *s2, size_t len);

- * Access builtin version by default. If one needs to use optimized version,
- * do "undef memcpy" in .c file and link against right string.c
- */
+/* Access builtin version by default. */
#define memcpy(d,s,l) __builtin_memcpy(d,s,l)
#define memset(d,c,l) __builtin_memset(d,c,l)
#define memcmp __builtin_memcmp