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

Tue Jun 19 00:47:06 PDT 2012

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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