llvm dev - Sep 2010 - [LLVMdev] Cross-compiling the ARM toolchain

> There isn't one at the moment, ideally it should figure it out, but I
haven't looked much into it - it may be that this isn't working yet.
I should say that I'm still a bit confused: Is it possible to build
for ARM CPUs now?
  1/ from which hosts (x86-*-* ?)
  2/ for which targets (arm-*-* ?)
  3/ what are the supported tools for ARM targets:
      a/ llvm-gcc (gcc 4.2)?
      b/ dragonegg (gcc 4.5)?
      c/ clang?

Thanks,
Manu

Maybe I'm misunderstanding your question, but clang/llvm is different from
gcc in that all targets are built in.  There's no building a specific target
version, like you have to do for binutils/gcc.

On Sep 11, 2010, at 8:44 AM, Emmanuel Blot wrote:
>> There isn't one at the moment, ideally it should figure it out, but
I haven't looked much into it - it may be that this isn't working yet.
> 
> I should say that I'm still a bit confused: Is it possible to build
> for ARM CPUs now?
>  1/ from which hosts (x86-*-* ?)
>  2/ for which targets (arm-*-* ?)
>  3/ what are the supported tools for ARM targets:
>      a/ llvm-gcc (gcc 4.2)?
>      b/ dragonegg (gcc 4.5)?
>      c/ clang?
> 
> Thanks,
> Manu
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Cameron Esfahani
dirty at apple.com

"The cake is a lie."

Common wisdom

>> I should say that I'm still a bit confused: Is it possible to build
>> for ARM CPUs now?
Yes!
>>  1/ from which hosts (x86-*-* ?)
AFAIK, all all supported platforms (x86, x86_64, etc)

>>  2/ for which targets (arm-*-* ?)
Virtually all. As far as I could test, all major architectures
(v4/v5/v6 + v7-A-R-M), although I'm still fighting with some Thumb
code generation. Could be my old gcc/binutils version (that still
doesn't even recognizes cortex-R4). You should check that yours is
really new (at least 2010) if you want v7R support.
>>  3/ what are the supported tools for ARM targets:
>>      a/ llvm-gcc (gcc 4.2)?
>>      b/ dragonegg (gcc 4.5)?
>>      c/ clang?
I haven't tested dragonegg, but clang and llvm-gcc do the job.
llvm-gcc seems to be more in sync with the ARM backend (for obvious
reasons), but it's a nightmare to compile it to the ARM backend. Clang
supports it out of the box.

Please, do have in mind that the code generated is by no means
super-optimized for each specific platform. There are some selected
features (mostly cortex-A*), but most of the code is generic to the
architecture or falls back to v4. So, if you're looking for great
optimizations GCC does for your specific SoC, you might not find it in
LLVM yet.

-- 
cheers,
--renato

> Virtually all. As far as I could test, all major architectures
> (v4/v5/v6 + v7-A-R-M), although I'm still fighting with some Thumb
> code generation.
Not a big issue for me: targets are ARMv4 (ARM7) and ARMv5 (ARM9)
"classic" CPUs - in ARM terminology. No cortex.
> I haven't tested dragonegg, but clang and llvm-gcc do the job.
> llvm-gcc seems to be more in sync with the ARM backend (for obvious
> reasons), but it's a nightmare to compile it to the ARM backend. Clang
> supports it out of the box.
I've been able to build clang + llvm from the SVN repository.

However my targets (arm-eabi) are relying on the "newlib" standard
library. I'm not sure how to build the llvm-gcc backend so that it
uses this library.
I'm used to build GCC (4.x) toolchains with newlib, but how can I do
the same with llvm-gcc ?
It seems that clang attemps to find the header files from the host
system dir, not from the target system dir, so I guess that I missed
an important option ... somewhere.

I've replaced the "arm-eabi-gcc" calls from my Makefiles with
"clang
-ccc-host-triple arm-eabi -ccc-gcc-name arm-eabi-gcc" but clang
probably needs some other options (?)

Thanks,
Emmanuel.