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liblzma: Avoid extern lzma_crc32_clmul() and lzma_crc64_clmul().

Browse source 
A CLMUL-only build will have the crcxx_clmul() inlined into
lzma_crcxx(). Previously a jump to the extern lzma_crcxx_clmul()
was needed. Notes about shared liblzma on ELF platforms:

  - On platforms that support ifunc and -fvisibility=hidden, this
    was silly because CLMUL-only build would have that single extra
    jump instruction of extra overhead.

  - On platforms that support neither -fvisibility=hidden nor linker
    version script (liblzma*.map), jumping to lzma_crcxx_clmul()
    would go via PLT so a few more instructions of overhead (still
    not a big issue but silly nevertheless).

There was a downside with static liblzma too: if an application only
needs lzma_crc64(), static linking would make the linker include the
CLMUL code for both CRC32 and CRC64 from crc_x86_clmul.o even though
the CRC32 code wouldn't be needed, thus increasing code size of the
executable (assuming that -ffunction-sections isn't used).

Also, now compilers are likely to inline crc_simd_body()
even if they don't support the always_inline attribute
(or MSVC's __forceinline). Quite possibly all compilers
that build the code do support such an attribute. But now
it likely isn't a problem even if the attribute wasn't supported.

Now all x86-specific stuff is in crc_x86_clmul.h. If other archs
The other archs can then have their own headers with their own
is_clmul_supported() and crcxx_clmul().

Another bonus is that the build system doesn't need to care if
crc_clmul.c is needed.

is_clmul_supported() stays as inline function as it's not needed
when doing a CLMUL-only build (avoids a warning about unused function).
This commit is contained in:
Lasse Collin 2023-10-20 23:35:10 +03:00
parent e3833e297d
commit 419f55f9df
7 changed files with 91 additions and 91 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

7
CMakeLists.txt
View file

@ -229,6 +229,7 @@ add_library(liblzma
src/liblzma/check/check.c
src/liblzma/check/check.h
src/liblzma/check/crc_common.h
src/liblzma/check/crc_x86_clmul.h
src/liblzma/common/block_util.c
src/liblzma/common/common.c
src/liblzma/common/common.h
@ -1000,11 +1001,7 @@ calculation if supported by the system" ON)
int main(void) { return 0; }
"
HAVE_USABLE_CLMUL)
if(HAVE_USABLE_CLMUL)
target_sources(liblzma PRIVATE src/liblzma/check/crc_clmul.c)
target_compile_definitions(liblzma PRIVATE HAVE_USABLE_CLMUL)
endif()
tuklib_add_definition_if(liblzma HAVE_USABLE_CLMUL)
endif()
endif()

1
configure.ac
View file

@ -1086,7 +1086,6 @@ __m128i my_clmul(__m128i a)
])
AC_MSG_RESULT([$enable_clmul_crc])
])
AM_CONDITIONAL([COND_CRC_CLMUL], [test "x$enable_clmul_crc" = xyes])
# Check for sandbox support. If one is found, set enable_sandbox=found.
#

6
src/liblzma/check/Makefile.inc
View file

@ -14,7 +14,8 @@ EXTRA_DIST += \
liblzma_la_SOURCES += \
check/check.c \
check/check.h \
check/crc_common.h
check/crc_common.h \
check/crc_x86_clmul.h
if COND_SMALL
liblzma_la_SOURCES += check/crc32_small.c
@ -27,9 +28,6 @@ if COND_ASM_X86
liblzma_la_SOURCES += check/crc32_x86.S
else
liblzma_la_SOURCES += check/crc32_fast.c
if COND_CRC_CLMUL
liblzma_la_SOURCES += check/crc_clmul.c
endif
endif
endif

9
src/liblzma/check/crc32_fast.c
View file

@ -15,6 +15,11 @@
#include "check.h"
#include "crc_common.h"
#ifdef CRC_CLMUL
# define BUILDING_CRC32_CLMUL
# include "crc_x86_clmul.h"
#endif
#ifdef CRC_GENERIC
@ -132,7 +137,7 @@ typedef uint32_t (*crc32_func_type)(
static crc32_func_type
crc32_resolve(void)
{
return is_clmul_supported() ? &lzma_crc32_clmul : &crc32_generic;
return is_clmul_supported() ? &crc32_clmul : &crc32_generic;
}
#if defined(HAVE_FUNC_ATTRIBUTE_IFUNC) && defined(__clang__)
@ -221,7 +226,7 @@ lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc)
return crc32_func(buf, size, crc);
#elif defined(CRC_CLMUL)
return lzma_crc32_clmul(buf, size, crc);
return crc32_clmul(buf, size, crc);
#else
return crc32_generic(buf, size, crc);

9
src/liblzma/check/crc64_fast.c
View file

@ -14,6 +14,11 @@
#include "check.h"
#include "crc_common.h"
#ifdef CRC_CLMUL
# define BUILDING_CRC64_CLMUL
# include "crc_x86_clmul.h"
#endif
#ifdef CRC_GENERIC
@ -97,7 +102,7 @@ typedef uint64_t (*crc64_func_type)(
static crc64_func_type
crc64_resolve(void)
{
return is_clmul_supported() ? &lzma_crc64_clmul : &crc64_generic;
return is_clmul_supported() ? &crc64_clmul : &crc64_generic;
}
#if defined(HAVE_FUNC_ATTRIBUTE_IFUNC) && defined(__clang__)
@ -160,7 +165,7 @@ lzma_crc64(const uint8_t *buf, size_t size, uint64_t crc)
//
// FIXME: Lookup table isn't currently omitted on 32-bit x86,
// see crc64_table.c.
return lzma_crc64_clmul(buf, size, crc);
return crc64_clmul(buf, size, crc);
#else
return crc64_generic(buf, size, crc);

64
src/liblzma/check/crc_common.h
View file

@ -108,70 +108,6 @@
# define CRC_USE_GENERIC_FOR_SMALL_INPUTS 1
# endif
*/
# if defined(_MSC_VER)
# include <intrin.h>
# elif defined(HAVE_CPUID_H)
# include <cpuid.h>
# endif
// is_clmul_supported() must be inlined in this header file because the
// ifunc resolver function may not support calling a function in another
// translation unit. Depending on compiler-toolchain and flags, a call to
// a function defined in another translation unit could result in a
// reference to the PLT, which is unsafe to do in an ifunc resolver. The
// ifunc resolver runs very early when loading a shared library, so the PLT
// entries may not be setup at that time. Inlining this function duplicates
// the function body in crc32_resolve() and crc64_resolve(), but this is
// acceptable because the function results in very few instructions.
static inline bool
is_clmul_supported(void)
{
int success = 1;
uint32_t r[4]; // eax, ebx, ecx, edx
#if defined(_MSC_VER)
// This needs <intrin.h> with MSVC. ICC has it as a built-in
// on all platforms.
__cpuid(r, 1);
#elif defined(HAVE_CPUID_H)
// Compared to just using __asm__ to run CPUID, this also checks
// that CPUID is supported and saves and restores ebx as that is
// needed with GCC < 5 with position-independent code (PIC).
success = __get_cpuid(1, &r[0], &r[1], &r[2], &r[3]);
#else
// Just a fallback that shouldn't be needed.
__asm__("cpuid\n\t"
: "=a"(r[0]), "=b"(r[1]), "=c"(r[2]), "=d"(r[3])
: "a"(1), "c"(0));
#endif
// Returns true if these are supported:
// CLMUL (bit 1 in ecx)
// SSSE3 (bit 9 in ecx)
// SSE4.1 (bit 19 in ecx)
const uint32_t ecx_mask = (1 << 1) | (1 << 9) | (1 << 19);
return success && (r[2] & ecx_mask) == ecx_mask;
// Alternative methods that weren't used:
// - ICC's _may_i_use_cpu_feature: the other methods should work too.
// - GCC >= 6 / Clang / ICX __builtin_cpu_supports("pclmul")
//
// CPUID decding is needed with MSVC anyway and older GCC. This keeps
// the feature checks in the build system simpler too. The nice thing
// about __builtin_cpu_supports would be that it generates very short
// code as is it only reads a variable set at startup but a few bytes
// doesn't matter here.
}
#endif
/// CRC32 implemented with the x86 CLMUL instruction.
extern uint32_t lzma_crc32_clmul(const uint8_t *buf, size_t size,
uint32_t crc);
/// CRC64 implemented with the x86 CLMUL instruction.
extern uint64_t lzma_crc64_clmul(const uint8_t *buf, size_t size,
uint64_t crc);
#endif

86
src/liblzma/check/crc_clmul.c → src/liblzma/check/crc_x86_clmul.h
View file

@ -1,11 +1,10 @@
///////////////////////////////////////////////////////////////////////////////
//
/// \file crc_clmul.c
/// \file crc_x86_clmul.h
/// \brief CRC32 and CRC64 implementations using CLMUL instructions.
///
/// lzma_crc32_clmul() and lzma_crc64_clmul() use 32/64-bit x86
/// SSSE3, SSE4.1, and CLMUL instructions. This is compatible with
/// Elbrus 2000 (E2K) too.
/// crc32_clmul() and crc64_clmul() use 32/64-bit x86 SSSE3, SSE4.1, and
/// CLMUL instructions. This is compatible with Elbrus 2000 (E2K) too.
///
/// They were derived from
/// https://www.researchgate.net/publication/263424619_Fast_CRC_computation
@ -27,9 +26,20 @@
//
///////////////////////////////////////////////////////////////////////////////
#include "crc_common.h"
// This file must not be included more than once.
#ifdef LZMA_CRC_X86_CLMUL_H
# error crc_x86_clmul.h was included twice.
#endif
#define LZMA_CRC_X86_CLMUL_H
#include <immintrin.h>
#if defined(_MSC_VER)
# include <intrin.h>
#elif defined(HAVE_CPUID_H)
# include <cpuid.h>
#endif
// EDG-based compilers (Intel's classic compiler and compiler for E2K) can
// define __GNUC__ but the attribute must not be used with them.
@ -225,12 +235,12 @@ calc_hi(uint64_t p, uint64_t a, int n)
}
*/
#ifdef HAVE_CHECK_CRC32
#ifdef BUILDING_CRC32_CLMUL
crc_attr_target
crc_attr_no_sanitize_address
extern uint32_t
lzma_crc32_clmul(const uint8_t *buf, size_t size, uint32_t crc)
static uint32_t
crc32_clmul(const uint8_t *buf, size_t size, uint32_t crc)
{
#ifndef CRC_USE_GENERIC_FOR_SMALL_INPUTS
// The code assumes that there is at least one byte of input.
@ -265,7 +275,7 @@ lzma_crc32_clmul(const uint8_t *buf, size_t size, uint32_t crc)
v0 = _mm_xor_si128(v0, v2); // [2]
return ~(uint32_t)_mm_extract_epi32(v0, 2);
}
#endif // HAVE_CHECK_CRC32
#endif // BUILDING_CRC32_CLMUL
/////////////////////
@ -299,7 +309,7 @@ calc_hi(uint64_t poly, uint64_t a)
}
*/
#ifdef HAVE_CHECK_CRC64
#ifdef BUILDING_CRC64_CLMUL
// MSVC (VS2015 - VS2022) produces bad 32-bit x86 code from the CLMUL CRC
// code when optimizations are enabled (release build). According to the bug
@ -318,8 +328,8 @@ calc_hi(uint64_t poly, uint64_t a)
crc_attr_target
crc_attr_no_sanitize_address
extern uint64_t
lzma_crc64_clmul(const uint8_t *buf, size_t size, uint64_t crc)
static uint64_t
crc64_clmul(const uint8_t *buf, size_t size, uint64_t crc)
{
#ifndef CRC_USE_GENERIC_FOR_SMALL_INPUTS
// The code assumes that there is at least one byte of input.
@ -366,4 +376,54 @@ lzma_crc64_clmul(const uint8_t *buf, size_t size, uint64_t crc)
# pragma optimize("", on)
#endif
#endif // HAVE_CHECK_CRC64
#endif // BUILDING_CRC64_CLMUL
// is_clmul_supported() must be inlined in this header file because the
// ifunc resolver function may not support calling a function in another
// translation unit. Depending on compiler-toolchain and flags, a call to
// a function defined in another translation unit could result in a
// reference to the PLT, which is unsafe to do in an ifunc resolver. The
// ifunc resolver runs very early when loading a shared library, so the PLT
// entries may not be setup at that time. Inlining this function duplicates
// the function body in crc32_resolve() and crc64_resolve(), but this is
// acceptable because the function results in very few instructions.
static inline bool
is_clmul_supported(void)
{
int success = 1;
uint32_t r[4]; // eax, ebx, ecx, edx
#if defined(_MSC_VER)
// This needs <intrin.h> with MSVC. ICC has it as a built-in
// on all platforms.
__cpuid(r, 1);
#elif defined(HAVE_CPUID_H)
// Compared to just using __asm__ to run CPUID, this also checks
// that CPUID is supported and saves and restores ebx as that is
// needed with GCC < 5 with position-independent code (PIC).
success = __get_cpuid(1, &r[0], &r[1], &r[2], &r[3]);
#else
// Just a fallback that shouldn't be needed.
__asm__("cpuid\n\t"
: "=a"(r[0]), "=b"(r[1]), "=c"(r[2]), "=d"(r[3])
: "a"(1), "c"(0));
#endif
// Returns true if these are supported:
// CLMUL (bit 1 in ecx)
// SSSE3 (bit 9 in ecx)
// SSE4.1 (bit 19 in ecx)
const uint32_t ecx_mask = (1 << 1) | (1 << 9) | (1 << 19);
return success && (r[2] & ecx_mask) == ecx_mask;
// Alternative methods that weren't used:
// - ICC's _may_i_use_cpu_feature: the other methods should work too.
// - GCC >= 6 / Clang / ICX __builtin_cpu_supports("pclmul")
//
// CPUID decding is needed with MSVC anyway and older GCC. This keeps
// the feature checks in the build system simpler too. The nice thing
// about __builtin_cpu_supports would be that it generates very short
// code as is it only reads a variable set at startup but a few bytes
// doesn't matter here.
}