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

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).

1 files changed, 0 insertions, 64 deletions

diff --git a/src/liblzma/check/crc_common.h b/src/liblzma/check/crc_common.h
index c949f793..552219fe 100644
--- a/src/liblzma/check/crc_common.h
+++ b/src/liblzma/check/crc_common.h
@@ -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