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lib: Prepare zstd for preboot environment, improve performance

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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
This commit is contained in:
Nick Terrell 2020-07-30 12:08:34 -07:00 committed by Ingo Molnar
parent 92ed301919
commit 6d25a633ea
2 changed files with 13 additions and 10 deletions
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9
lib/zstd/fse_decompress.c
View File

@ -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
****************************************************************/

14
lib/zstd/zstd_internal.h
View File

@ -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;