llvm dev - Jun 2012 - [LLVMdev] Is cross-compiling for ARM on x86 with llvm/Clang possible?

Hello list,

I wonder if llvm/Clang can compile C or C++ for ARM from on x86.

http://comments.gmane.org/gmane.comp.compilers.clang.devel/8896

The talk above answered 'NO' to my question, which means Clang is not
yet
able to cross compile for ARM on X86.

Is the answer still correct for my question?

I saw somewhere that Clang supports ARM on Darwin only. Then is the cross
compiling possible only on Darwin not on linux or FreeBSD?

If the cross compiling is supported, is there any documentation on how to
do it?

Thank you very much in advance.

Best regards
Journeyer
-- 
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Journeyer J. Joh
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On Sat, Jun 16, 2012 at 20:20:23 +0900, Journeyer J. Joh
wrote:
> I wonder if llvm/Clang can compile C or C++ for ARM from on x86.
Yes. I use
  clang -emit-llvm -ccc-host-triple arm-unknown-linux-gnu -I /..arm../include/
to generate LLVM bitcode files for ARM. llc then automagically knows to
generate ARM assembly, and ARM binutils take it from there.
> If the cross compiling is supported, is there any documentation on how to
> do it?
Dunno. Last time I looked, the documentation of clang's command line flags
disagreed with reality, and the -ccc-host-triple flag wasn't documented
anywhere. This might have changed in the meantime.

-- 
Gergö Barany, research assistant                 gergo at complang.tuwien.ac.at
Institute of Computer Languages      http://www.complang.tuwien.ac.at/gergo/
Vienna University of Technology                       Tel: +43-1-58801-58522
Argentinierstrasse 8/E185, 1040 Wien, Austria         Fax: +43-1-58801-18598

Hi,  Gergö

Cross compiling with Clang/llvm is much easier than with llvm-gcc or gcc!

Thank you very much!!
Though I am so much new to llvm that I can't prove your answer right way,
my friend verified your answer.

Thank you very much.

Sincerely
Journeyer

(PS. Sorry I am resending same email because I sent only to you. I want to
say thank you on the mail list.)


2012/6/18 Gergö Barany <gergo at complang.tuwien.ac.at>
> On Sat, Jun 16, 2012 at 20:20:23 +0900, Journeyer J. Joh wrote:
> > I wonder if llvm/Clang can compile C or C++ for ARM from on x86.
>
> Yes. I use
>  clang -emit-llvm -ccc-host-triple arm-unknown-linux-gnu -I
> /..arm../include/
> to generate LLVM bitcode files for ARM. llc then automagically knows to
> generate ARM assembly, and ARM binutils take it from there.
>
> > If the cross compiling is supported, is there any documentation on how
to
> > do it?
>
> Dunno. Last time I looked, the documentation of clang's command line
flags
> disagreed with reality, and the -ccc-host-triple flag wasn't documented
> anywhere. This might have changed in the meantime.
>
> --
> Gergö Barany, research assistant
> gergo at complang.tuwien.ac.at
> Institute of Computer Languages
> http://www.complang.tuwien.ac.at/gergo/
> Vienna University of Technology                       Tel:
> +43-1-58801-58522
> Argentinierstrasse 8/E185, 1040 Wien, Austria         Fax:
> +43-1-58801-18598
>


-- 
----------------------------------------
Journeyer J. Joh
o o s a p r o g r a m m e r
a t
g m a i l  d o t  c o m
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On Sat, Jun 16, 2012 at 08:20:23PM +0900, Journeyer J. Joh
wrote:
> If the cross compiling is supported, is there any documentation on how to
> do it?
The short version is: assuming you have a cross-binutils installation
using e.g. x86_64--netbsd-as and x86_64--netbsd-ld, you add a symlink
called x86_64--netbsd-clang to clang and just call that with an
appropiate --sysroot to make it find your target include headers and
libraries. Substitute x86_64--netbsd with the triple of your choice.
Alternative, call clang -target x86_64--netbsd ...

Joerg

Hello Gergö, Joerg and people on our list

With your kind answer, I tried to build a hello world program for
ARM(arm-none-linux-gnueabi) on my x86-64 PC.

Thank you we verified the generated bitcode. The only thing remained is
linking.

Let me brief what I did so far.

1. Built Clang/llvm in a way explained in
http://clang.llvm.org/get_started.html on Ubuntu 11.10 x86-64 PC
2. Downloaded gcc-4.0 toolchain binaries for x86-64 from
http://www.gnuarm.com/
3. Wrote a hello.c as shown below.

#include <stdio.h>

int main(void)
{
printf("\nHello World!\n\n");

return 0;
}

4. Tested as shown below.

./clang -v -emit-llvm -ccc-host-triple arm-none-linux-gnueabi
-I/home/hum/Documents/Projects/llvm_clang/gnuarm-4.0.2/arm-elf/include
-L/home/hum/Documents/Projects/llvm_clang/gnuarm-4.0.2/arm-elf/bin hello.c

5. Received an output and an error message shown below.

clang version 3.2 (trunk 158657)
Target: arm-none-linux-gnueabi
Thread model: posix
 "/home/hum/Documents/Projects/llvm_clang/build/Debug+Asserts/bin/clang"
-cc1 -triple armv4t-none-linux-gnueabi -emit-llvm-bc -disable-free
-main-file-name hello.c -mrelocation-model static -mdisable-fp-elim
-fmath-errno -mconstructor-aliases -target-abi aapcs-linux -target-cpu
arm7tdmi -mfloat-abi soft -target-feature +soft-float-abi
-target-linker-version 2.21.53.20110810 -momit-leaf-frame-pointer -v
-resource-dir
/home/hum/Documents/Projects/llvm_clang/build/Debug+Asserts/bin/../lib/clang/3.2
-I /home/hum/Documents/Projects/llvm_clang/gnuarm-4.0.2/arm-elf/include
-fmodule-cache-path /var/tmp/clang-module-cache -internal-isystem
/usr/local/include -internal-isystem
/home/hum/Documents/Projects/llvm_clang/build/Debug+Asserts/bin/../lib/clang/3.2/include
-internal-externc-isystem /include -internal-externc-isystem /usr/include
-fno-dwarf-directory-asm -fdebug-compilation-dir
/home/hum/Documents/Projects/llvm_clang/build/Debug+Asserts/bin
-ferror-limit 19 -fmessage-length 212 -mstackrealign -fno-signed-char
-fgnu-runtime -fobjc-runtime-has-arc -fobjc-runtime-has-weak
-fobjc-fragile-abi -fdiagnostics-show-option -fcolor-diagnostics -o
/tmp/hello-T8xLAt.o -x c hello.c
clang -cc1 version 3.2 based upon LLVM 3.2svn default target
x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
 /home/hum/Documents/Projects/llvm_clang/gnuarm-4.0.2/arm-elf/include
 /usr/local/include
 /home/hum/Documents/Projects/llvm_clang/build/Debug+Asserts/bin/../lib/clang/3.2/include
 /usr/include
End of search list.
 "/usr/bin/ld" -z relro -X --hash-style=gnu --build-id --eh-frame-hdr
-m
armelf_linux_eabi -dynamic-linker /lib/ld-linux.so.3 -o a.out crt1.o crti.o
crtbegin.o
-L/home/hum/Documents/Projects/llvm_clang/gnuarm-4.0.2/arm-elf/bin
-L/usr/lib/../lib32 -L/lib -L/usr/lib -plugin
/home/hum/Documents/Projects/llvm_clang/build/Debug+Asserts/bin/../lib/LLVMgold.so
/tmp/hello-T8xLAt.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc
--as-needed -lgcc_s --no-as-needed crtend.o crtn.o
/usr/bin/ld: unrecognised emulation mode: armelf_linux_eabi
Supported emulations: elf_x86_64 elf32_x86_64 elf_i386 i386linux elf_l1om
elf_k1om
clang: error: linker command failed with exit code 1 (use -v to see
invocation)

6. The problem occurred when clang starts to link with ld. Clang tried to
use the ld in a wrong place - "/usr/bin/ld". So I tried it  myself
like
below.

/home/hum/Documents/Projects/llvm_clang/gnuarm-4.0.2/arm-elf/bin/ld -z
relro -X --hash-style=gnu --build-id --eh-frame-hdr -m armelf_linux_eabi -o
a.out crt1.o crti.o crtbegin.o
-L/home/hum/Documents/Projects/llvm_clang/gnuarm-4.0.2/arm-elf/bin -plugin
/home/hum/Documents/Projects/llvm_clang/build/Debug+Asserts/bin/../lib/LLVMgold.so
/tmp/hello-Fe7D3Y.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc
--as-needed -lgcc_s --no-as-needed crtend.o crtn.o

7. And received an error message below.

/home/hum/Documents/Projects/llvm_clang/gnuarm-4.0.2/arm-elf/bin/ld:
unrecognised emulation mode: armelf_linux_eabi
Supported emulations: armelf

8. I found a talk about this problem below.

http://sourceware.org/bugzilla/show_bug.cgi?id=12643

9. But I don't know where ld/configure.tgt exists.


Let me list up things I want to know.

A. For the #6 above, how can I make clang use ld in the toolchain not int
the system?
B. For the #7 above, how can I trouble-shoot this, I couldn't find .tgt
file introduced in the #9 above.
C. For all the steps above, am I doing all right, I doubt if
www.gnuarm.comis trustful.

For Joerg, I tried using -isysroot as a clang option, but I couldn't find
any difference it brings.

Thank you very much.

Sincerely

Journeyer J. Joh


2012/6/18 Joerg Sonnenberger <joerg at britannica.bec.de>
> On Sat, Jun 16, 2012 at 08:20:23PM +0900, Journeyer J. Joh wrote:
> > If the cross compiling is supported, is there any documentation on how
to
> > do it?
>
> The short version is: assuming you have a cross-binutils installation
> using e.g. x86_64--netbsd-as and x86_64--netbsd-ld, you add a symlink
> called x86_64--netbsd-clang to clang and just call that with an
> appropiate --sysroot to make it find your target include headers and
> libraries. Substitute x86_64--netbsd with the triple of your choice.
> Alternative, call clang -target x86_64--netbsd ...
>
> Joerg
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>


-- 
----------------------------------------
Journeyer J. Joh
o o s a p r o g r a m m e r
a t
g m a i l  d o t  c o m
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