SimpleScalar Notes

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[ 2006-April-08 10:29 ]

SimpleScalar is a CPU simulator that is very useful for computer architecture research. However, it has not been updated for a long time, and I've found a couple of small bugs. Additionally, it took me a bit of work to be able to figure out how to compile a binary without linking against the C library.

Minimal SimpleScalar Binary

Typically SimpleScalar binaries link against the C library. This is fine unless you are mucking around with the CPU internals and have broken backwards compatibility. I've created a minimal "library" that you can use to link C programs: libinit.s. Basically, the steps are:

Assemble this library (as -o libinit.o libinit.s)
Compile your C program (gcc -c program.c). You may wish to use the -ffast-math switch to get GCC to convert some math function calls into instructions. For example, it will convert calls to the C library's sqrt function into calls to the sqrt instruction.
Link the two together (ld -o program program.o libinit.o)

The result is a C program that does not use the C library. Of course, this also means you can't use any of the C library functions, such as printf or malloc. You may also need my loader patch to get SimpleScalar to execute your binary.

Loader Patch

The SimpleScalar loader has a bug: it will fail to run binaries if they are missing some sections. Here is a tiny patch to the loader to fix this problem. Without this patch, it will print: fatal: could not read text section from executable." Interestingly enough, the Alpha code already had part of this fix.

Mac OS X patch