lib: Prepare zstd for preboot environment, improve performance

These changes are necessary to get the build to work in the preboot
environment, and to get reasonable performance:

- Remove a double definition of the CHECK_F macro when the zstd
  library is amalgamated.

- Switch ZSTD_copy8() to __builtin_memcpy(), because in the preboot
  environment on x86 gcc can't inline `memcpy()` otherwise.

- Limit the gcc hack in ZSTD_wildcopy() to the broken gcc version. See
  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81388.

ZSTD_copy8() and ZSTD_wildcopy() are in the core of the zstd hot loop.
So outlining these calls to memcpy(), and having an extra branch are very
detrimental to performance.

Signed-off-by: Nick Terrell <terrelln@fb.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20200730190841.2071656-2-nickrterrell@gmail.com

diff --git a/lib/zstd/fse_decompress.c b/lib/zstd/fse_decompress.c
index a84300e5a0132247d7ce18caeab0bb093b2305a3..0b353530fb3f300396a71c285b28f68c7b96eb89 100644 (file)
--- a/lib/zstd/fse_decompress.c
+++ b/lib/zstd/fse_decompress.c
@@ -47,6 +47,7 @@
 ****************************************************************/
 #include "bitstream.h"
 #include "fse.h"
+#include "zstd_internal.h"
 #include <linux/compiler.h>
 #include <linux/kernel.h>
 #include <linux/string.h> /* memcpy, memset */
@@ -60,14 +61,6 @@
                enum { FSE_static_assert = 1 / (int)(!!(c)) }; \
        } /* use only *after* variable declarations */
 
-/* check and forward error code */
-#define CHECK_F(f)                  \
-       {                           \
-               size_t const e = f; \
-               if (FSE_isError(e)) \
-                       return e;   \
-       }
-
 /* **************************************************************
 *  Templates
 ****************************************************************/

diff --git a/lib/zstd/zstd_internal.h b/lib/zstd/zstd_internal.h
index 1a79fab9e13add613828fa9f285c705e08a23066..dac753397f868d736005da8857f9961f5d2080e4 100644 (file)
--- a/lib/zstd/zstd_internal.h
+++ b/lib/zstd/zstd_internal.h
@@ -127,7 +127,14 @@ static const U32 OF_defaultNormLog = OF_DEFAULTNORMLOG;
 *  Shared functions to include for inlining
 *********************************************/
 ZSTD_STATIC void ZSTD_copy8(void *dst, const void *src) {
-       memcpy(dst, src, 8);
+       /*
+        * zstd relies heavily on gcc being able to analyze and inline this
+        * memcpy() call, since it is called in a tight loop. Preboot mode
+        * is compiled in freestanding mode, which stops gcc from analyzing
+        * memcpy(). Use __builtin_memcpy() to tell gcc to analyze this as a
+        * regular memcpy().
+        */
+       __builtin_memcpy(dst, src, 8);
 }
 /*! ZSTD_wildcopy() :
 *   custom version of memcpy(), can copy up to 7 bytes too many (8 bytes if length==0) */
@@ -137,13 +144,16 @@ ZSTD_STATIC void ZSTD_wildcopy(void *dst, const void *src, ptrdiff_t length)
        const BYTE* ip = (const BYTE*)src;
        BYTE* op = (BYTE*)dst;
        BYTE* const oend = op + length;
-       /* Work around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81388.
+#if defined(GCC_VERSION) && GCC_VERSION >= 70000 && GCC_VERSION < 70200
+       /*
+        * Work around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81388.
         * Avoid the bad case where the loop only runs once by handling the
         * special case separately. This doesn't trigger the bug because it
         * doesn't involve pointer/integer overflow.
         */
        if (length <= 8)
                return ZSTD_copy8(dst, src);
+#endif
        do {
                ZSTD_copy8(op, ip);
                op += 8;