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When a gem5 op is triggered using a KVM MMIO exit event, the PC has already been advanced beyond the offending instruction. Normally when a system call or gem5 op is triggered, the PC has not advanced because the instruction hasn't actually finished executing. This means that if a gem5 op, and by extension a system call in SE mode, want to advance the PC to the instruction after the gem5 op, they have to check whether they were triggered from KVM. To avoid having to special case these sorts of situations (currently only in the clone system call), we can have the code which dispatches to gem5 ops from KVM adjust the next PC so that it points to what the current PC is. That way the PC can be advanced unconditionally, and will point to the instruction after the one that triggered the call. To be fully consistent, we would also need to adjust the current PC. That would be non-trivial since we'd have to figure out where the current instruction started, and that may not even be possible to unambiguously determine given x86's instruction structure. Then we would also need to restore the original PC to avoid confusing KVM. Change-Id: I9ef90b2df8e27334dedc25c59eb45757f7220eea Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/38486 Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Maintainer: Andreas Sandberg <andreas.sandberg@arm.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/about, and for more information about building the simulator and getting started please see http://www.gem5.org/documentation and http://www.gem5.org/documentation/learning_gem5/introduction. 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/documentation/general_docs/building 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 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/documentation/general_docs/building for more details and options. 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. If you have questions, please send mail to gem5-users@gem5.org Enjoy using gem5 and please share your modifications and extensions.