Difference between revisions of "Frequently Asked Questions"

Revision as of 16:57, 28 June 2006

Device Related

How can I see the packets on the ethernet link?

• By creating a Etherdump object, setting it's file parameter, and setting the dump parameter on the EtherLink to it. This is most easily accomplished by setting the enivornment variable -EDUMPFILE=<file>. The resulting file will be named <file> and be in a standard pcap format.

OS/Linux Related

How do I create a disk image?

• You can use the mkblankimage.sh script that is provided in our distribution of linux-dist to create a blank image of arbitrary size.

How do I add files to a disk image?

• Using either sudo or the root account run /bin/mount -o loop,offset=32256 /z/foo.img /mount/point. You can then copy the desired files to the image. Remember to unmount it before running the simulator with /bin/umount /mount/point or you may get unexpected results.

How do I compile a kernel to run on M5 in full-system mode?

• You need either a cross-compiler to compile Alpha binaries, or you can compile directly on an Alpha you may have. Since most people don't have Alphas, using a cross-compiler is the most common option. Then, in the top level of the Linux tree you want to build, just type 'make ARCH=alpha CROSS_COMPILE=/path/to/your/xcompiler/bin/alpha-unknown-linux-gnu-'. This tells the Makefile that you want to build an alpha binary, and where to find the cross compiler to do so.

How do I build a cross compiler?

• Download cross-tool here. It is a script to simplify the creation of cross-compilers. There is a good howto on the website to get you started. You'll want to build cross-compiler for Alphas.

I can't compile the patched 2.6.13 kernel, what do I do?

• Try using crosstool-0.38 with the following params. You can set them by changing your demo-alpha.sh file to point to the appropriate gcc-glibc file combination, and this particular setup has been known to build the patched 2.6.13 kernel:
  • TARGET=alpha-unknown-linux-gnu
  • PREFIX=/usr/local/cross
  • BUILD_DIR=$CROSS_DIR/$TARGET-$HOSTNAME
  • SRC_DIR=$CROSS_DIR/src
  • BINUTILS_DIR=binutils-2.16.1
  • GCC_DIR=gcc-4.0.2
  • GCC_LANGUAGES="c,c++"
  • GLIBC_DIR=glibc-2.3.5
  • GLIBCTHREADS_FILENAME=glibc-linuxthreads-2.3.5
  • LINUX_DIR=linux-2.6.13
  • GCC_DIR=gdb-6.3
  • TARGET_CFLAGS=-O

Running Related

How do I get my Alpha executable to work in syscall emulation mode?

• M5 does not support dynamically linking libraries in syscall emulation mode. You must recompile the executable and have it statically linked. See the gcc man page for more information on statically linking your binary.

How many CPUs can M5 run?

• There is no strict limit however the Alpha platform we support (Tsunami) only has support for 4 processors. We made some additions to the platform both in the simulator and in Linux to support up to 64 processors. However simulating 64 processors will be quite slow, and the Linux scheduler doesn't seem particularly good at scheduling large amounts of processors.

How do I see what options I can set?

• Using the '-h' flag will show what options M5 can take in general. Running m5.debug foo.py -h (or any m5 binary variant) will list all options that are available based on M5's internal options and the options defined in the .py file.

How do I run multiprogram workloads on M5?

How do I use the sampler?

Debugging and Error Related

When running my program I get an error "Error: syscall <syscall name here> unimplemented."

• That means that one of the libraries that you are linking with uses a syscall that is not emulated. You can do a man on the syscall name to see what the syscall is supposed to do and then try to implement at least whatever functionality your application needs. Or you can try the quick & dirty approach, which is to change the function pointer for syscall in arch/<arch>/<os>/<os>.cc from unimplementedFunc to ignoreFunc, which will make it print a warning and keep going rather than terminate with an error. No guarantees that your program won't crash because of this though.

How do I access reference counted pointers in GDB?

• Objects such as DynInsts are reference counted, making it slightly harder to obtain the data inside. In gdb you must access them through the pointer that is stored in the ref counted pointer, which is called data. Thus given a ref counted pointer ptr, in gdb you would say (gdb) ptr->data to get the pointer to the actual object.

I get an error "undefined reference to `void foo()'" when the compiler is doing the final linking.

• This is due to having a function that is declared but never defined. Either you forgot to define it, or are not compiling in the file that defines it. In the case of templated code, you may be including the wrong file or you may not have manually instantiated a templated class that needs to be manually instantiated.

I've created a new SimObject but it doesn't seem to be recognized when I run M5.

• You'll need to put the python object file in src/python/m5/objects/, and edit src/python/m5/objects/__init__.py to include your object.

What does this error mean warn: setsysinfo: ignoring ieee_set_fp_control() arg 0x11ff96f98?

• That and similar errors are warning you that the system call that sets IEEE FP control register is being ignored. This register primarily enables/disables different kinds of FP traps (underflow, overflow, inexact, etc.). Since M5 doesn't implement those traps anyway there's no point in implementing the syscall. It's pretty unlikely your application relies on them, so as long as everything else seems to work you can ignore the warning.

Extending M5 Related

How would I define a new CPU Model for M5?

The easiest way is to derive a new C++ class of your CPU Model from M5 CPU Models that are already defined. The easiest model to start with is probably the 'AtomicSimpleCPU' located in the 'm5/cpu/simple' directory.

After you create a separate directory for your code (e.g. 'm5/cpu/my_cpu'), there are a couple files that need to be updated:

• m5/SConstruct: Add the name of your CPU model to the 'ALL_CPU_MODELS' list
• m5/cpu/SConscript: Add your CPU model and the relevant files that need to be built in here
• m5/cpu/static_inst.hh: Put a forward class declaration of your model in here
• m5/cpu/cpu_models.py: Add in CPU Model-specific information for the ISA Parser (make sure to check out the documentation on how the ISA Description Language works)

Now build your model: scons build/ALPHA_SE/m5.debug CPU_MODELS=MY_CPU

How would I define a new ISA for M5?

Miscellaneous

Where are the classes for each ISA instruction? Where are the execute() methods for the StaticInst class?

• Both the classes and the execute() methods are generated through Python upon building any version of M5. For example, After building ALPHA_SE, they will be located in the build/ALPHA_SE/arch/alpha/ folder. The key files are decoder.hh, decoder.cc (which describe the ISA instructions), and *_exec.cc (which describe the execute() methods). The definitions for both exist in the .isa files found in src/arch/*/isa/, which are processed by src/arch/isa_parser.py to generate the previously mentioned .hh/.cc files.

Is fast-forwarding supported in SMT mode?

• It is not currently supported. The SimpleCPU doesn't support SMT, so it doesn't support fast-forwarding in SMT mode. However it should be feasible given some hacking on the SimpleCPU or the Sampler.

I've created a new file, how do I get SCons to compile it.

• Add the file to the SConscript in the current directory or if it doesn't exist the SConscript in closest parent directory.

How do I use a normal variable in a statistic formula?

• This is not supported. Just create a Scalar<> statistic that does the same thing as your normal variable and use that in the formula instead.

What are all these *_impl.hh files?

• There is a lot of templated code used within M5, and these *_impl.hh are used to make it a little easier to organize things. Normally template functions must be entirely included in the header file in order to not require the programmer to manually instantiate the copies of the template functions. However, when you have an entire class that's templated, the header files quickly become bloated and too big, except for small helper classes. Thus we put the declarations in the header file as normal, the definitions in the *_impl.hh file, and the manual instantiations in the *.cc file. This makes it easier to sort out the instantiations from the definitions. Also if there are only a few templated functions inside a non-templated class, it may be possible to include the functions in the *_impl.hh file and not have to manually instantiate the functions. You just need to include the *_impl.hh file in any .cc files that use the templated function. See mem/packet{.hh|_impl.hh|.cc} for an example.

What if SCons complains that it can't find a file I just deleted?

• Delete the scons.dblite file in the m5 directory.

Which config files are used for syscall emulation? Full system mode?