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Daniel Verkamp d9a67ea922
Manually preserve rbx across cpuid instruction (#851) 
* Manually preserve rbx across cpuid instruction

This fixes an issue observed when using __cpuid and __cpuid_count with
Address Sanitizer enabled: the generated code uses the rbx register to
access ASAN tracking information without reloading it after cpuid,
resulting in a segfault since the rbx register is overwritten by cpuid
(https://crbug.com/1072045).

This seems like a compiler backend bug, and indeed there is a
long-standing LLVM bug report about a very similar issue:
https://bugs.llvm.org/show_bug.cgi?id=17907

To work around this issue, we can manually preserve the rbx register
contents in the inline assembly.  This is the approach taken by LLVM's
own host cpuid detection code (lib/Host/Support.cpp).  The original rbx
value is stashed in rsi, which is then swapped with rbx to restore the
original value as well as keep the output ebx value from the CPUID
instruction to be used as an output of the inline assembly.

The rbx clobber is also removed; this seems ineffective, and it
conflicts with the ebx output of the inline assembly (ebx is a
subregister of rbx): "Note that clobbering named registers that are also
present in output constraints is not legal."
(https://llvm.org/docs/LangRef.html#clobber-constraints)

* Add link to LLVM bug in cpuid workaround comment
2020-04-29 01:50:13 +01:00
..
src
Manually preserve rbx across cpuid instruction (#851)
2020-04-29 01:50:13 +01:00
tests
Add Icelake avx512 features (#838)
2020-01-26 13:10:29 -06:00
build.rs
Fix libcore build
2019-02-12 01:02:07 +01:00
Cargo.toml
Remove azure pipelines badges
2019-10-10 12:42:41 +02:00
LICENSE-APACHE
Add README and licenses to core_arch
2019-01-22 18:49:24 +01:00
LICENSE-MIT
Add README and licenses to core_arch
2019-01-22 18:49:24 +01:00
README.md
Remove azure pipelines badges
2019-10-10 12:42:41 +02:00
rustfmt.toml
Replace rustfmt::skip custom inner attribute with rustfmt.toml
2019-10-26 18:46:22 +02:00

README.md

core::arch - Rust's core library architecture-specific intrinsics

core_arch_crate_badge core_arch_docs_badge

The core::arch module implements architecture-dependent intrinsics (e.g. SIMD).

Usage

core::arch is available as part of libcore and it is re-exported by libstd. Prefer using it via core::arch or std::arch than via this crate. Unstable features are often available in nightly Rust via the feature(stdsimd).

Using core::arch via this crate requires nightly Rust, and it can (and does) break often. The only cases in which you should consider using it via this crate are:

  • if you need to re-compile core::arch yourself, e.g., with particular target-features enabled that are not enabled for libcore/libstd. Note: if you need to re-compile it for a non-standard target, please prefer using xargo and re-compiling libcore/libstd as appropriate instead of using this crate.

  • using some features that might not be available even behind unstable Rust features. We try to keep these to a minimum. If you need to use some of these features, please open an issue so that we can expose them in nightly Rust and you can use them from there.

Documentation

License

core_arch is primarily distributed under the terms of both the MIT license and the Apache License (Version 2.0), with portions covered by various BSD-like licenses.

See LICENSE-APACHE, and LICENSE-MIT for details.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in core_arch by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.