diff options
Diffstat (limited to 'src/liblzma/check/crc_common.h')
| -rw-r--r-- | src/liblzma/check/crc_common.h | 52 |
1 files changed, 49 insertions, 3 deletions
diff --git a/src/liblzma/check/crc_common.h b/src/liblzma/check/crc_common.h index 51ddd9d5..1783b5e7 100644 --- a/src/liblzma/check/crc_common.h +++ b/src/liblzma/check/crc_common.h @@ -99,11 +99,57 @@ # 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 -/// Detect at runtime if the CPU supports the x86 CLMUL instruction when -/// both the generic and CLMUL implementations are built. -extern bool lzma_is_clmul_supported(void); + // 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, |