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The minor CPU was using a PCState object both to track redirects when taking a branch, etc, and to track where to fetch a line of memory from. It would need to create a new PCState object, or at least update the existing one, whenever it needed to advance to the next line. This is problematic since it means the minor CPU needs to know how to create or set a PCState object, and since it by necessity only understands the most basic aspect of a PCState, what the address is, it can only set that, with all the other potential attributes staying at their old values or getting set to some default. Instead, this change separates the two. There is now a PC which is used for redirects which the later stages will only pick up if there is a change in "sequence", the same behavior as before. This PC will only ever be set when changing sequence, and will otherwise not be meaningful/useful. There is also now a separate fetch address which is what the fetch stage uses to get new lines. This was all the PC value that was artificially updated was used for anyway. Change-Id: Ia64bbe21e980566ae77786999689c9c8a94e9378 Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/52048 Tested-by: kokoro <noreply+kokoro@google.com> Reviewed-by: ZHENGRONG WANG <seanyukigeek@gmail.com> Maintainer: ZHENGRONG WANG <seanyukigeek@gmail.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, 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 these tools. Once you have all dependencies resolved, type 'scons build/<CONFIG>/gem5.opt' where CONFIG is one of the options in build_opts like ARM, NULL, MIPS, POWER, SPARC, X86, Garnet_standalone, etc. This will build an optimized version of the gem5 binary (gem5.opt) with the the specified configuration. See http://www.gem5.org/documentation/general_docs/building for more details and options. The main source tree includes these subdirectories: - build_opts: pre-made default configurations for gem5 - build_tools: tools used internally by gem5's build process. - configs: example simulation configuration scripts - ext: less-common external packages needed to build gem5 - include: include files for use in other programs - site_scons: modular components of the build system - 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 may need compiled system firmware, kernel binaries and one or more disk images, depending on gem5's configuration and what type of workload you're trying to run. Many of those resources can be downloaded from http://resources.gem5.org, and/or from the git repository here: https://gem5.googlesource.com/public/gem5-resources/ If you have questions, please send mail to gem5-users@gem5.org Enjoy using gem5 and please share your modifications and extensions.