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ec14a00925
Emulating LL/SC with cmpxchg is not correct, since it can suffer from the ABA problem. Portable parallel code, however, is written assuming only cmpxchg--and not LL/SC--is available. This means that in practice emulating LL/SC with cmpxchg is a viable alternative. The appended emulates LL/SC pairs in ARM with cmpxchg helpers. This works in both user and system mode. In usermode, it avoids pausing all other CPUs to perform the LL/SC pair. The subsequent performance and scalability improvement is significant, as the plots below show. They plot the throughput of atomic_add-bench compiled for ARM and executed on a 64-core x86 machine. Hi-res plots: http://imgur.com/a/aNQpB atomic_add-bench: 1000000 ops/thread, [0,1] range 9 ++---------+----------+----------+----------+----------+----------+---++ +cmpxchg +-E--+ + + + + + | 8 +Emaster +-H--+ ++ | | | 7 ++E ++ | | | 6 ++++ ++ | | | 5 ++ | ++ 4 ++ | ++ | | | 3 ++ | ++ | | | 2 ++ | ++ |H++E+--- +++ ---+E+------+E+------+E| 1 +++ +E+-----+E+------+E+------+E+------+E+-- +++ +++ ++ ++H+ + +++ + +++ ++++ + + + | 0 ++--H----H-+-----H----+----------+----------+----------+----------+---++ 0 10 20 30 40 50 60 Number of threads atomic_add-bench: 1000000 ops/thread, [0,2] range 16 ++---------+----------+---------+----------+----------+----------+---++ +cmpxchg +-E--+ + + + + + | 14 ++master +-H--+ ++ | | | 12 ++| ++ | E | 10 ++| ++ | | | 8 ++++ ++ |E+| | | | | 6 ++ | ++ | | | 4 ++ | ++ | +E+--- +++ +++ +++ ---+E+------+E| 2 +H+ +E+------E-------+E+-----+E+------+E+------+E+-- +++ + | + +++ + ++++ + + + | 0 ++H-H----H-+-----H----+---------+----------+----------+----------+---++ 0 10 20 30 40 50 60 Number of threads atomic_add-bench: 1000000 ops/thread, [0,128] range 70 ++---------+----------+---------+----------+----------+----------+---++ +cmpxchg +-E--+ + + + ++++ + | 60 ++master +-H--+ ----E------+E+-------++ | -+E+--- +++ +++ +E| | +++ ---- +++ ++| 50 ++ +++ ---+E+- ++ | -E--- | 40 ++ ---+++ ++ | +++--- | | -+E+ | 30 ++ +++---- ++ | +E+ | 20 ++ +++-- ++ | +E+ | |+E+ | 10 +E+ ++ + + + + + + + | 0 +HH-H----H-+-----H----+---------+----------+----------+----------+---++ 0 10 20 30 40 50 60 Number of threads atomic_add-bench: 1000000 ops/thread, [0,1024] range 120 ++---------+---------+----------+---------+----------+----------+---++ +cmpxchg +-E--+ + + + + + | | master +-H--+ ++| 100 ++ ----E+ | +++ ---+E+--- ++| | --E--- +++ | 80 ++ ---- +++ ++ | ---+E+- | 60 ++ -+E+-- ++ | +++ ---- +++ | | -+E+- | 40 ++ +++---- ++ | +++ ---+E+ | | -+E+--- | 20 ++ +E+ ++ |+E+++ | +E+ + + + + + + | 0 +HH-H---H--+-----H---+----------+---------+----------+----------+---++ 0 10 20 30 40 50 60 Number of threads Backports commit 354161b37c6465a32073eac5f16fa35939af2bb4 from qemu |
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| msvc | ||
| qemu | ||
| samples | ||
| tests | ||
| .appveyor.yml | ||
| .gitignore | ||
| .travis.yml | ||
| AUTHORS.TXT | ||
| Brewfile | ||
| ChangeLog | ||
| config.mk | ||
| COPYING | ||
| COPYING.LGPL2 | ||
| COPYING_GLIB | ||
| CREDITS.TXT | ||
| install-cmocka-linux.sh | ||
| list.c | ||
| make.sh | ||
| Makefile | ||
| msvc.bat | ||
| pkgconfig.mk | ||
| README.md | ||
| uc.c | ||
| windows_export.bat | ||
Unicorn Engine
Unicorn is a lightweight, multi-platform, multi-architecture CPU emulator framework based on QEMU.
Unicorn offers some unparalleled features:
- Multi-architecture: ARM, ARM64 (ARMv8), M68K, MIPS, SPARC, and X86 (16, 32, 64-bit)
- Clean/simple/lightweight/intuitive architecture-neutral API
- Implemented in pure C language, with bindings for Crystal, Clojure, Visual Basic, Perl, Rust, Ruby, Python, Java, .NET, Go, Delphi/Free Pascal and Haskell.
- Native support for Windows & *nix (with Mac OSX, Linux, *BSD & Solaris confirmed)
- High performance via Just-In-Time compilation
- Support for fine-grained instrumentation at various levels
- Thread-safety by design
- Distributed under free software license GPLv2
Further information is available at http://www.unicorn-engine.org
License
This project is released under the GPL license.
Compilation & Docs
See docs/COMPILE.md file for how to compile and install Unicorn.
More documentation is available in docs/README.md.
Contact
Contact us via mailing list, email or twitter for any questions.
Contribute
If you want to contribute, please pick up something from our Github issues.
We also maintain a list of more challenged problems in a TODO list.
CREDITS.TXT records important contributors of our project.