llvm dev - Nov 2013 - [LLVMdev] Targeting ARM Cortex-a9 from x86_64 with clang

On 26 November 2013 16:44, Renato Golin <renato.golin at linaro.org>
wrote:
> On 26 November 2013 15:36, Rob Stewart <robstewart57 at gmail.com>
wrote:
>>
>> $ clang -v -target armv7a-linux-eabi -mcpu=cortex-a9 -mfloat-abi=soft
>> -mfpu=neon helloworld.c
>
> Hi Rod,
I'm honoured. (But Rob is also OK) :-)
> You need cross-binutils installed on your box. If you use Debian, there are
> packages (gcc-4.7-arm-linux-gnueabi and friends). Other distros may have
> similar packages, but you can always download the Linaro toolchain
> (http://releases.linaro.org/latest/components/toolchain).
>
> Supposing you already have it, and it's in the PATH, Clang only
recognizes
> it automatically if your triple is identical to the name of your cross
> compiler (See "Toolchain Options" in the referred doc). That
means, you
> either need to have an "armv7a-linux-eabi-gcc" on the path, or
you have to
> change your triple to something like "arm-linux-gnueabi", because
that's
> what your cross-GCC will probably be called. The -mcpu will take care of
> choosing v7A.
So on my Fedora box, I've installed packages gcc-arm-linux-gnu.x86_64
and cross-binutils-common.noarch . Moreover, the first of these two
packages provide `/usr/bin/arm-linux-gnu-gcc`
$ repoquery -lq gcc-arm-linux-gnu.x86_64
Repository google-chrome is listed more than once in the configuration
/usr/bin/arm-linux-gnu-cpp
/usr/bin/arm-linux-gnu-gcc
/usr/bin/arm-linux-gnu-gcov
/usr/lib/gcc/arm-linux-gnueabi
/usr/lib/gcc/arm-linux-gnueabi/4.8.1
/usr/lib/gcc/arm-linux-gnueabi/4.8.1/crtbegin.o
...

The -target that appears to be recognised by clang is `arm-none-eabi`.
However, I'm now falling in to another trap.
$ clang -v -target arm-none-eabi -mcpu=cortex-a9 -mfloat-abi=soft helloworld.c
...
arm-none-eabi-gcc: fatal error: selected multilib '.' not installed

I've put the -v output to gist: https://gist.github.com/robstewart57/7676030

On 27 November 2013 13:57, Rob Stewart <robstewart57 at gmail.com>
wrote:
>> Hi Rod,
>
> I'm honoured. (But Rob is also OK) :-)
Haha! That was my best typo ever! ;)

> So on my Fedora box, I've installed packages gcc-arm-linux-gnu.x86_64
> and cross-binutils-common.noarch.
I'm not sure Clang understands "arm-linux-gnu" as a triple. The
driver
is not the most sane code in Clang, so it might have holes in it that
won't make sense.

It is worth opening a new thread on cfe-dev@ discussing the possible
outcome of using arm-linux-gnu or arm-linux-androideabi as your triple
and get your toolchain to be detected correctly on Fedora.

> The -target that appears to be recognised by clang is `arm-none-eabi`.
That triple is normally used when targeting bare-metal ARM targets,
which I don't think is your case.

I can see from your output, all seem fine until...

> arm-none-eabi-gcc: fatal error: selected multilib '.' not installed
Normally, the problem with this is that you have libraries compiled
with hard-float and is trying to compile code with soft-float. But you
should focus on getting Clang to recognize your original triple first,
I think.

cheers,
--renato

On 11/27/2013 07:57 AM, Rob Stewart wrote:
> On 26 November 2013 16:44, Renato Golin <renato.golin at linaro.org>
wrote:
>> On 26 November 2013 15:36, Rob Stewart <robstewart57 at
gmail.com> wrote:
>>> $ clang -v -target armv7a-linux-eabi -mcpu=cortex-a9
-mfloat-abi=soft
>>> -mfpu=neon helloworld.c
>> Hi Rod,
> I'm honoured. (But Rob is also OK) :-)
>
>> You need cross-binutils installed on your box. If you use Debian, there
are
>> packages (gcc-4.7-arm-linux-gnueabi and friends). Other distros may
have
>> similar packages, but you can always download the Linaro toolchain
>> (http://releases.linaro.org/latest/components/toolchain).
>>
>> Supposing you already have it, and it's in the PATH, Clang only
recognizes
>> it automatically if your triple is identical to the name of your cross
>> compiler (See "Toolchain Options" in the referred doc). That
means, you
>> either need to have an "armv7a-linux-eabi-gcc" on the path,
or you have to
>> change your triple to something like "arm-linux-gnueabi",
because that's
>> what your cross-GCC will probably be called. The -mcpu will take care
of
>> choosing v7A.
> So on my Fedora box, I've installed packages gcc-arm-linux-gnu.x86_64
> and cross-binutils-common.noarch . Moreover, the first of these two
> packages provide `/usr/bin/arm-linux-gnu-gcc`
> $ repoquery -lq gcc-arm-linux-gnu.x86_64
> Repository google-chrome is listed more than once in the configuration
> /usr/bin/arm-linux-gnu-cpp
> /usr/bin/arm-linux-gnu-gcc
> /usr/bin/arm-linux-gnu-gcov
> /usr/lib/gcc/arm-linux-gnueabi
> /usr/lib/gcc/arm-linux-gnueabi/4.8.1
> /usr/lib/gcc/arm-linux-gnueabi/4.8.1/crtbegin.o
> ...
>
> The -target that appears to be recognised by clang is `arm-none-eabi`.
> However, I'm now falling in to another trap.
> $ clang -v -target arm-none-eabi -mcpu=cortex-a9 -mfloat-abi=soft
helloworld.c
> ...
> arm-none-eabi-gcc: fatal error: selected multilib '.' not installed
>
> I've put the -v output to gist:
https://gist.github.com/robstewart57/7676030
>
Your link says that clang is using gcc to compile rather than compiling 
directly. You might want to look at the ELLCC project, which is designed 
for just the sort of cross compilation you are trying to do. 
http://ellcc.org

-Rich

On 27 November 2013 14:55, Richard Pennington <rich at pennware.com>
wrote:
> Your link says that clang is using gcc to compile rather than compiling
> directly. You might want to look at the ELLCC project, which is designed
for
> just the sort of cross compilation you are trying to do. http://ellcc.org
Hi Rich,

No, his output only has gcc to assemble and link:

"/usr/bin/arm-none-eabi-gcc" -v -mcpu=cortex-a9 -mfloat-abi=soft -c -o
/tmp/helloworld-2n4ZGp.o -x assembler /tmp/helloworld-Iarp5R.s
"/usr/bin/arm-none-eabi-gcc" -v -mcpu=cortex-a9 -mfloat-abi=soft -o
a.out /tmp/helloworld-2n4ZGp.o

Clang normally calls GAS in case "-integrated-as" is not specified for
ARM.

Btw, Rod, you might try the integrated assembler, too.

cheers,
--renato