Building gem5

Platforms

• Linux, BSD, MacOS X, Solaris, etc
• 64 bit machines help quite a bit

Tools

• GCC/G++ 4.4+ (or clang 2.9+)
• Python 2.4+
• SCons 0.98.1+
  • http://www.scons.org
• SWIG 1.3.40+
  • http://www.swig.org

If using Ubuntu install

• apt-get install python-dev scons m4 build-essential g++ swig zlib-dev

Compile Targets

build:

• build/<isa>/<binary>

ISAs:

• ARM, ALPHA, MIPS, SPARC, POWER, X86, RISCV

Binaries

• gem5.debug
  • debug build, symbols, tracing, assert
• gem5.opt
  • optimized build, symbols, tracing, assert
• gem5.fast
  • optimized build, no debugging, no symbols, no tracing, no assertions
• gem5.prof
  • gem5.fast + profiling support

Sample Compile

[/work/gem5] scons build/ARM/gem5.opt –j4

Running Simulation

[/work/gem5] ./build/ARM/gem5.opt -h

Usage 
===== 
 gem5.opt [gem5 options] script.py [script options] 
 
 gem5 is copyrighted software; use the --copyright option for details. 
 
Options 
======= 
--version                show program's version number and exit 
--help, -h               show this help message and exit 
--build-info, -B         Show build information 
--copyright, -C          Show full copyright information 
--readme, -R             Show the readme 
--outdir=DIR, -d DIR     Set the output directory to DIR [Default: m5out] 
--redirect-stdout, -r    Redirect stdout (& stderr, without -e) to file 
--redirect-stderr, -e    Redirect stderr to file 
--stdout-file=FILE       Filename for -r redirection [Default: simout] 
--stderr-file=FILE       Filename for -e redirection [Default: simerr] 
--interactive, -i        Invoke the interactive interpreter after running the 
                         script 
--pdb                    Invoke the python debugger before running the script 
--path=PATH[:PATH], -p PATH[:PATH] 
                         Prepend PATH to the system path when invoking the 
                         script 

Running Simulation

Statistics Options 
------------------ 
--stats-file=FILE  Sets the output file for statistics [Default: stats.txt] 
 
Configuration Options 
--------------------- 
--dump-config=FILE  Dump configuration output file [Default: config.ini] 
--json-config=FILE  Create JSON output of the configuration [Default: config.json] 
 
Debugging Options 
----------------- 
--debug-break=TIME[,TIME] 
                         Cycle to create a breakpoint 
--debug-help             Print help on trace flags 
--debug-flags=FLAG[,FLAG] 
                         Sets the flags for tracing (-FLAG disables a flag) 
--remote-gdb-port=REMOTE_GDB_PORT 
                         Remote gdb base port (set to 0 to disable listening) 
 
Trace Options 
------------- 
--trace-start=TIME      Start tracing at TIME (must be in ticks) 
--trace-file=FILE       Sets the output file for tracing [Default: cout] 
--trace-ignore=EXPR     Ignore EXPR sim objects

gem5 has two fundamental modes

Full system (FS)

• For booting operating systems
• Models bare hardware, including devices
• Interrupts, exceptions, privileged instructions, fault handlers
• Simulated UART output
• Simulated frame buffer output

Syscall emulation (SE)

• For running individual applications, or set of applications on MP
• Models user-visible ISA plus common system calls
• System calls emulated, typically by calling host OS
• Simplified address translation model, no scheduling

Now dependent on how you run the binary

• No longer need to compile different binaries

Sample Run – Syscall Emulation

 [/work/gem5] ./build/ARM/gem5.opt configs/example/se.py  \
              -c tests/test-progs/hello/bin/arm/linux/hello 

Sample Run – Full System

Command Line: 
22:13:19 [/work/gem5] ./build/ARM/gem5.opt configs/example/fs.py  
… 
info: kernel located at: /dist/binaries/vmlinux.arm.smp.fb.2.6.38.8 
Listening for system connection on port 5900 
Listening for system connection on port 3456 
0: system.remote_gdb.listener: listening for remote gdb #0 on port 7000 
info: Using bootloader at address 0x80000000 
**** REAL SIMULATION **** 
info: Entering event queue @ 0.  Starting simulation... 
warn: The clidr register always reports 0 caches. 
warn: clidr LoUIS field of 0b001 to match current ARM implementations. 


Terminal: 
22:13:19 [/work/gem5] ./util/term/m5term 127.0.0.1 3456 
==== m5 slave terminal: Terminal 0 ==== 
[0.000000] Linux version 2.6.38.8-gem5 (saidi@zeep) (gcc version 4.5.2 (Sourcery G++ Lite 2011.03-41) ) 
#1 SMP Mon Aug 15 21:18:38 EDT 2011 
[0.000000] CPU: ARMv7 Processor [350fc000] revision 0 (ARMv7), cr=10c53c7f 
[0.000000] CPU: VIPT nonaliasing data cache, VIPT nonaliasing instruction cache 
[0.000000] Machine: ARM-RealView PBX
...
starting pid 354, tty '': '/sbin/getty -L ttySA0 38400 vt100' 
AEL login:

Sample Run – Behind the scenes

gem5 architecture