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

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On Mon, Sep 7, 2015 at 11:20 PM, Sedat Dilek <sedat.dilek@gmail.com> wrote:
> On Mon, Sep 7, 2015 at 10:59 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>> On Mon, Sep 7, 2015 at 1:53 PM, Sedat Dilek <sedat.dilek@gmail.com> 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 "$@".
>>
>>  - or even just use a symlink (the script has the advantage that you
>> can play with the options etc too)
>>
>>  - change the shell script (or symlink) itself, and make sure to use
>> the same CC for "make" at all times, so that the build script never
>> sees that the underlying command is now different.
>>
>> It should work fine, I've done it a couple of times (although
>> admittedly not recently)
>>
>
> OK, I have created a mycompiler shell-script and use that for CC and
> HOSTCC in my own build-script.
>
> Using CLANG...
>
> [ /usr/bin/mycompiler ]
>
> #!/bin/bash
>
> clang "$@"
> - 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 ]
>
> #!/bin/bash
>
> 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
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
>
> Thanks, that helped me a lot.
>

Sadly, this trick does not work here with Linux v4.2.

- Sedat -
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Thread

Use (two) different compilers at build-time? Sedat Dilek <sedat.dilek@gmail.com> - 2015-09-07 21:20 +0200
  Re: Use (two) different compilers at build-time? Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-07 22:20 +0200
    Re: Use (two) different compilers at build-time? Sedat Dilek <sedat.dilek@gmail.com> - 2015-09-07 22:40 +0200
      Re: Use (two) different compilers at build-time? Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-07 22:50 +0200
        Re: Use (two) different compilers at build-time? Linus Torvalds <torvalds@linux-foundation.org> - 2015-09-07 23:00 +0200
          Re: Use (two) different compilers at build-time? Sedat Dilek <sedat.dilek@gmail.com> - 2015-09-07 23:30 +0200
            Re: Use (two) different compilers at build-time? Sedat Dilek <sedat.dilek@gmail.com> - 2015-09-08 00:40 +0200
              Re: Use (two) different compilers at build-time? Sedat Dilek <sedat.dilek@gmail.com> - 2015-09-08 07:50 +0200
                Re: Use (two) different compilers at build-time? Sedat Dilek <sedat.dilek@gmail.com> - 2015-09-08 08:00 +0200
        Re: Use (two) different compilers at build-time? Sedat Dilek <sedat.dilek@gmail.com> - 2015-09-07 23:00 +0200
  Re: Use (two) different compilers at build-time? Fengguang Wu <fengguang.wu@intel.com> - 2015-09-10 02:30 +0200
    Re: Use (two) different compilers at build-time? Sedat Dilek <sedat.dilek@gmail.com> - 2015-09-13 17:30 +0200
      Re: Use (two) different compilers at build-time? Fengguang Wu <fengguang.wu@intel.com> - 2015-09-14 04:20 +0200

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