Re: Use (two) different compilers at build-time?

From: Sedat Dilek
Date: Mon Sep 07 2015 - 17:20:16 EST

On Mon, Sep 7, 2015 at 10:59 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, Sep 7, 2015 at 1:53 PM, Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote:
>> That does not work.
> .. because you didn't do what I told you to do.
>> I copied a gcc-compiled percpu.o OR deleted/renamed percpu.o and
>> re-invoked make - this starts a complete new build from scratch.
> Right. Because you changed the compiler name, so now the build system
> realizes that the old build instructions are stale.
> Which is why you have to:
>>> Use a wrapper around the compiler (and point to that wrapper with the
>>> "to switch compilers from under the make, without the build paths
>>> changing (because otherwise our makefile auto-machinery notices that
>>> flags and command changed).
>>> Use CC (or CROSS_COMPILE) to point at your wrapper.
>> No idea how to realize that, sorry.
> Literally just do something like this:
> - have a shell script call "mycompiler" and make it do gcc/llvm "$@".
> - or even just use a symlink (the script has the advantage that you
> can play with the options etc too)
> - change the shell script (or symlink) itself, and make sure to use
> the same CC for "make" at all times, so that the build script never
> sees that the underlying command is now different.
> It should work fine, I've done it a couple of times (although
> admittedly not recently)

OK, I have created a mycompiler shell-script and use that for CC and
HOSTCC in my own build-script.

Using CLANG...

[ /usr/bin/mycompiler ]


clang "$@"
- EOF -

$ mycompiler --version
clang version 3.7.0 (tags/RELEASE_370/final)
Target: x86_64-unknown-linux-gnu
Thread model: posix

Switching to GCC...

[ /usr/bin/mycompiler ]


gcc-4.9 "$@"
- EOF -

$ mycompiler --version
gcc-4.9 (Ubuntu 4.9.2-0ubuntu1~12.04) 4.9.2
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO

Thanks, that helped me a lot.

- Sedat -
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at