[U-Boot] [PATCH v3 0/8] add clang support for some ARM boards

Jeroen Hofstee
2014-09-11T11:17:20Z

Hello Albert,

On do, 2014-09-11 at 10:32 +0200, Albert ARIBAUD wrote:

>
> On Wed, 10 Sep 2014 20:08:50 +0200, Jeroen Hofstee
> <jeroen@myspectrum.nl> wrote:
>
> > Changes since v2:
> > - As Albert pointed out the clang instructions don't work with
> > Debian based binary packages. While I was aware of that it is
> > for a different reason then I thought, it is not that ARM is not
> > enabled as a backend but older versions are a bit more picky on
> > the target argument and don't tolerate a trailing dash to it as
> > used for CROSS_COMPILE etc. The README is updated accordingly.
> >
> > As a side note clang3.5-svn as shipped in Ubuntu is not the 3.5
> > release but an snapshot of some svn commit and hence explain why
> > the recompiled 3.5 can behave different then the ubuntu clang-3.5.
> > Since it misses some patches, the clang3.5-svn can build less
> > boards then 3.4 or an actual 3.5 release.
> >
> > - While add it, include Masahiro suggestion to also use c++ instead
> > of g++.
> > - Drop dependencies from the cover-letter as they are merged.
> > - only patch 7/8 and 8/8 are reposted. 1..6 are the same as v2.
>
> Thanks, tested building rpi_b, it works now.
>
> The, tested on versatileqemu out of curiosity and got the following
> results:
>
> 1.
>
> clang warns about Unused static functions in common/console.c, namely
> console_printdevs and console_doenv (1). Why gcc does not flag this?
> We have -Wall set which is supposed to imply -Wunused-functions.

It is a gcc feature, see [1]: "Warn whenever a static function is
declared but not defined or a _non-inline static function_ is unused.
This warning is enabled by -Wall."

>
> There is also an unused variable warning in disk/part.c28
> (block_drvr). I haven't looked at why clang warns about it and not gcc,
> but it could raise the same question as the functions above.
>

Also a gcc feature, see [2]. The constant is indeed not used.

> 2.
>
> clang errors on arch/arm/lib/cache.c:28 for this:
> asm("0: mrc p15, 0, r15, c7, c10, 3\n\t" "bne 0b\n" : : : "memory");
> and that is a clang mistake, as for ARM926EJS r15 is a valid (albeit
> quite special semantically) Rd for Test and Clean DCache, see page 2-24.
>

This is the integrated-as complaining (the README tells you to disable
it for the moment). The clang folks push UAL hard, up to a point we need
to think about minimum gcc version etc. To avoid that, I just left out
such changes and just use gas instead, at least for the time being.
Below are some changes to compile versatileqemu with llvm integrated-as
and gcc/gas. No idea if it actually boots though.

> Jeroen, do you feel like raising point 2 to the clang/LLVM folks?

It is removed on purpose as far as I understood. I don't think they
regards it as a bug, see obfuscated patch below.

> Other than that, the patch series seems to be good. I'll apply it
> soonish.
>

Thanks,
Jeroen

[1] https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
[2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=13029

s/~/-/g

~~~