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Build with -mpclmul when avx is available #1038

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Build with -mpclmul when avx is available #1038

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wqfish
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@wqfish wqfish commented Sep 18, 2025 •
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The code fails to build with RUSTFLAGS='-C target-cpu=x86-64-v3' on Linux. The error message indicates that -mpclmul is missing:

  cargo:warning=In file included from rocksdb/util/crc32c.cc:52:                                      
  cargo:warning=rocksdb/util/crc32c.cc: In function 'uint64_t rocksdb::crc32c::CombineCRC(size_t, uint64_t, uint64_t, uint64_t, const uint64_t*)':                                                           
  cargo:warning=rocksdb/util/crc32c.cc:553:21: error: '__builtin_ia32_pclmulqdq128' needs isa option -mpclmul -msse2                                                                                         
  cargo:warning=  553 |   const auto res0 = _mm_clmulepi64_si128(crc0_xmm, multiplier, 0x00);         
  cargo:warning=      |                     ^~~~~~~~~~~~~~~~~~~~                                      
  cargo:warning=rocksdb/util/crc32c.cc:555:21: error: '__builtin_ia32_pclmulqdq128' needs isa option -mpclmul -msse2                                                                                         
  cargo:warning=  555 |   const auto res1 = _mm_clmulepi64_si128(crc1_xmm, multiplier, 0x10);         
  cargo:warning=      |                     ^~~~~~~~~~~~~~~~~~~~

It looks like RocksDB defines __PCLMUL__ as long as __AVX__ is detected:

https://github.com/facebook/rocksdb/blob/631fb8670b077aa80c3953ceb3ed5c82649db515/port/lang.h#L78-L83

So we have to do the same: add -mpclmul if avx is detected.

@wqfish
Build with -mpclmul when avx is available
ea5557d 
The code fails to build with `RUSTFLAGS='-C target-cpu=x86-64-v3'`. The error
message indicates that `-mpclmul` is missing.

It looks like RocksDB defines `__PCLMUL__` as long as `__AVX__` is detected:

https://github.com/facebook/rocksdb/blob/631fb8670b077aa80c3953ceb3ed5c82649db515/port/lang.h#L78-L83

So we have to do the same: add `-mpclmul` if `avx` is detected.
aleksuss
aleksuss reviewed Sep 18, 2025
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librocksdb-sys/build.rs
config.flag_if_supported("-mlzcnt");
}
if !target.contains("android") && target_features.contains(&"pclmulqdq") {
if !target.contains("android")
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Should it be:

Suggested change
if !target.contains("android")
if target.contains("windows")

?
As I can see it's related to MSVC?

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First, I'm not familiar with android and why it's here in the first place, so I didn't touch it.

Second, while the comments in port/lang.h mentions MSVC, that section of code is not guarded by any #if/#ifdef, so it applies to everything. I actually ran into this failure when building on Linux.

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@aleksuss aleksuss aleksuss left review comments

@zaidoon1 zaidoon1 zaidoon1 approved these changes

@stanislav-tkach stanislav-tkach Awaiting requested review from stanislav-tkach

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@wqfish @aleksuss @zaidoon1