Re: about size optimizations (Re: Not as much ccache win as I expected)

[Jamie Lokier <jamie@shareable.org>]

David Woodhouse wrote:
> On Sat, 2008-06-14 at 10:56 +0100, Oleg Verych wrote:
> > I saw that. My point is pure text processing. But as it seems doing
> > `make` is a lot more fun than to do `sh` && `sed`.
> 
> The problem is that it _isn't_ pure text processing. There's more to
> building with --combine than that, and we really do want the compiler to
> do it.
> 
> _Sometimes_ you can just append C files together and they happen to
> work. But not always. A simple case where it fails would be when you
> have a static variable with the same name in two different files.

I suspect the simplest way to adapt an existing makefile is:

    1. Replace each compile command "gcc args... file.c -o file.o"
       with "gcc -E args... file.c -o file.o.i".

    2. Replace each incremental link "ld -r -o foo.o files..." with
       "cat `echo files... | sed 's/$/.i/'` > foo.o.i".

    3. Similar replacement for each "ar" command making .a files.

    4. Replace the main link "ld -o vmlinux files..." with
       "gcc -o vmlinux --combine -fwhole-program `echo files... | sed 's/$/.i/'`".

You can do this without changin the Makefile, if you provide suitable
scripts on $PATH for the make.

-- Jamie