Ccache

According to the manpage, ccache is a fast C/C++ compiler cache. It works with the gcc and clang compilers (or alike).

Reference

• ccache on GitHub
• ccache manual.
• https://software.intel.com/en-us/articles/accelerating-compilation-part-1-ccache

Install

On Debian / Ubuntu, ccache is available as a standard package:

sudo apt install ccache

To use ccache for compiling, just create a few symlinks. For instance, to use ccache with gcc and clang-3.6:

sudo ln -sf /usr/bin/ccache /usr/local/bin/gcc
sudo ln -sf /usr/bin/ccache /usr/local/bin/clang-3.6

This will work as long as the directory with symlinks comes before the path to the compiler (which is usually in /usr/bin).

Usage

• Collect ccache usage statistics:

ccache -s

• Set cache size:

ccache -M 2G

Troubleshoot

Get ccache logging

Enabling ccache logging may help troubleshooting issues. Just add to ~/.ccache/ccache.conf:

log_file = ccache.log

From now on, ccache will produce a detailed log in the current directory.

ccache ignore .include directive in assembly file

ccache ignores .include directives in assembly file (*.s or *.S). As a result, if the included file changes, ccache does not detect it and still provides the old object.

Workaround:

• Use .incbin directive instead [1]. The problem is that clang ignores .incbin directive. The fix is to use a conditional compilation like:

# Pretend we use .incbin directive to prevent ccache to cache this file (clang ignores ;incbin, and ccache ignores .include)
.if 1
.include "file.s"
.else
.incbin "file.s"
.endif

• Better yet, use *.S file that enables preprocessor, and use a standard #include directive, which will be correctly catched by ccache:

#include "file.S"