Large projects like the Linux kernel, which are mostly C, use the preprocessor in .S files quite heavily. Linux has hardly any .s files. ~/linux$ find . -na

Large projects like the Linux kernel, which are mostly C, use the preprocessor in .S files quite heavily. Linux has hardly any .s files. ~/linux$ find . -name '*.s' ./arch/x86/kernel/asm-offsets.s ./kernel/bounds.s ./scripts/mod/devicetable-offsets.s But there are plenty of .S files with #includes ~/linux$ $ find . -name '*.S' | xargs grep -l '#include' | wc -l 1217 Edit: simplify command as suggested