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FutexMap::wakeup is called when the futex(TGT_FUTEX_WAKE syscall is done. FutexMap maintains a list of sleeping threads for each futex address added on FutexMap::suspend, and entries are removed from the list at FutexMap::wakeup. The problem is that this system was not taking into account that threads can be woken up by memory accesses to locked addresses via the path: SimpleThread::activate BaseSimpleCPU::wakeup AbstractMemory::checkLockedAddrList AbstractMemory::access DRAMCtrl::recvAtomic CoherentXBar::recvAtomicBackdoor SimpleExecContext::writeMem which happens on trivial pthread examples on ARM at least. The instruction that locked memory in those test cases was LDAXR. This could lead futex(TGT_FUTEX_WAKE to awake a thread that is already awake but is first on the sleeping thread list, instead of a sleeping one, which can lead all threads to incorrectly sleep and in turn to "simulate() limit reached". To implement this, ThreadContext::activate return now returns a boolean that indicates if the state changed. suspend and halt are also modified to also return a boolean in the same case for symmetry, although this is not strictly necessary for the current patch. Change-Id: Ia6b4d3e6148c64721d810b8f1fffaa208a394b06 Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21606 Reviewed-by: Brandon Potter <Brandon.Potter@amd.com> Maintainer: Brandon Potter <Brandon.Potter@amd.com> Tested-by: kokoro <noreply+kokoro@google.com>
This is the gem5 simulator. The main website can be found at http://www.gem5.org A good starting point is http://www.gem5.org/Introduction, and for more information about building the simulator and getting started please see http://www.gem5.org/Documentation and http://www.gem5.org/Tutorials. To build gem5, you will need the following software: g++ or clang, Python (gem5 links in the Python interpreter), SCons, SWIG, zlib, m4, and lastly protobuf if you want trace capture and playback support. Please see http://www.gem5.org/Dependencies for more details concerning the minimum versions of the aforementioned tools. Once you have all dependencies resolved, type 'scons build/<ARCH>/gem5.opt' where ARCH is one of ALPHA, ARM, NULL, MIPS, POWER, SPARC, or X86. This will build an optimized version of the gem5 binary (gem5.opt) for the the specified architecture. See http://www.gem5.org/Build_System for more details and options. With the simulator built, have a look at http://www.gem5.org/Running_gem5 for more information on how to use gem5. The basic source release includes these subdirectories: - configs: example simulation configuration scripts - ext: less-common external packages needed to build gem5 - src: source code of the gem5 simulator - system: source for some optional system software for simulated systems - tests: regression tests - util: useful utility programs and files To run full-system simulations, you will need compiled system firmware (console and PALcode for Alpha), kernel binaries and one or more disk images. Please see the gem5 download page for these items at http://www.gem5.org/Download If you have questions, please send mail to gem5-users@gem5.org Enjoy using gem5 and please share your modifications and extensions.