Process for reducing the size of an executable

Question

I\'m producing a hex file to run on an ARM processor which I want to keep below 32K. It\'s currently a lot larger than that and I wondered if someone might have some advice

Answer 1

To answer this specific need:

•I want to omit those functions (if possible) but I can't find what's calling them!! Could be called from any number of library functions I guess.

If you want to analyze your code base to see who calls what, by whom a given function is being called and things like that, there is a great tool out there called "Understand C" provided by SciTools.

https://scitools.com/

I have used it very often in the past to perform static code analysis. It can really help to determine library dependency tree. It allows to easily browse up and down the calling tree among other things.

They provide a limited time evaluation, then you must purchase a license.

Answer 2

Andrew EdgeCombe has a great list, but if you really want to scrape every last byte, sstrip is a good tool that is missing from the list and and can shave off a few more kB.

For example, when run on strip itself, it can shave off ~2kB.

From an old README (see the comments at the top of this indirect source file):

sstrip is a small utility that removes the contents at the end of an ELF file that are not part of the program's memory image.

Most ELF executables are built with both a program header table and a section header table. However, only the former is required in order for the OS to load, link and execute a program. sstrip attempts to extract the ELF header, the program header table, and its contents, leaving everything else in the bit bucket. It can only remove parts of the file that occur at the end, after the parts to be saved. However, this almost always includes the section header table, and occasionally a few random sections that are not used when running a program.

Note that due to some of the information that it removes, a sstrip'd executable is rumoured to have issues with some tools. This is discussed more in the comments of the source.

Also... for an entertaining/crazy read on how to make the smallest possible executable, this article is worth a read.