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For most system calls, it doesn't matter if the PC is advanced to the instruction after the system call instruction before or after the system call itself is invoked, because the system call itself doesn't interact with it. For some system calls however, specifically "clone" and "execve", advancing the PC *after* the system call complicates things, because it means the system call needs to set the PC to something that will equal the desired value only *after* it's advanced. By setting the PC *before* the system call, the system call can set the PC to whatever it needs to. This means the new cloned context doesn't need to advance the PC because it's already advanced, and execve doesn't need to set NPC, it can leave the PC set to the correct value from the entry point set during Process initialization. Change-Id: I830607c2e9adcc22e738178fd3663417512e2e56 Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/53983 Reviewed-by: Jason Lowe-Power <power.jg@gmail.com> Maintainer: Jason Lowe-Power <power.jg@gmail.com> Tested-by: kokoro <noreply+kokoro@google.com> Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com> Maintainer: Matt Sinclair <mattdsinclair@gmail.com> Reviewed-by: Kyle Roarty <kyleroarty1716@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.