[llvm-dev] Cross-compiling for ARM on x86 with llvm/Clang

[via llvm-dev]

Hello list

I have some problems when using x86 cross-compile the arm progress.

 

First I know a way to get aarch64 binary in x86 with llvm/clang.

There need two things prepared for cross-compile.

1.  GUN ARM toolchain à  apt-get install gcc-arm-linux-gnueabi

2.  Clang/llvm compile à http://clang.llvm.org/get_started.html

clang -emit-llvm -target aarch64 helloworld.c -I /usr/aarch64-linux-gnu/include -c  

(can get helloworld.bc)

llc helloworld.bc -o helloworld.s

aarch64-linux-gnu-gcc helloworld.s -o helloworld

From the cmd above, I can get the aarch64 binary which is function well in aarch64 machine.

But, Is there other way that I can get aarch64 without gcc.

When I try to use below:

clang -v -target arm-linux-gnueabi --sysroot=/usr/arm-linux-gnueabi/ helloworld.c -o hello 

I get:

Obfuscator-LLVM clang version 3.6.1 (tags/RELEASE_361/final) (based on Obfuscator-LLVM 3.6.1)

Target: arm--linux-gnueabi

Thread model: posix

 "/usr/local/bin/clang-3.6" -cc1 -triple armv4t--linux-gnueabi -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -main-file-name arm.c -mrelocation-model static -mthread-model posix -mdisable-fp-elim -fmath-errno -masm-verbose -mconstructor-aliases -target-cpu arm7tdmi -target-feature +soft-float-abi -target-abi aapcs-linux -mfloat-abi soft -v -dwarf-column-info -resource-dir /usr/local/bin/../lib/clang/3.6.1 -isysroot /usr/arm-linux-gnueabi/ -internal-isystem /usr/arm-linux-gnueabi//usr/local/include -internal-isystem /usr/local/bin/../lib/clang/3.6.1/include -internal-externc-isystem /usr/arm-linux-gnueabi//include -internal-externc-isystem /usr/arm-linux-gnueabi//usr/include -fdebug-compilation-dir /home/zyj/Desktop -ferror-limit 19 -fmessage-length 80 -mstackrealign -fno-signed-char -fobjc-runtime=gcc -fdiagnostics-show-option -fcolor-diagnostics -o /tmp/helloworld-6b36a6.o -x c helloworld.c

clang -cc1 version 3.6.1 based upon Obfuscator-LLVM 3.6.1 default target i386-pc-linux-gnu

ignoring nonexistent directory "/usr/arm-linux-gnueabi//usr/local/include"

ignoring nonexistent directory "/usr/arm-linux-gnueabi//usr/include"

#include "..." search starts here:

#include <...> search starts here:

 /usr/local/bin/../lib/clang/3.6.1/include

 /usr/arm-linux-gnueabi//include

End of search list.

 "/usr/local/bin/ld" --sysroot=/usr/arm-linux-gnueabi/ -z relro -X --hash-style=gnu --build-id --eh-frame-hdr -m armelf_linux_eabi -dynamic-linker /lib/ld-linux.so.3 -o hello /usr/arm-linux-gnueabi//lib/../lib/crt1.o /usr/arm-linux-gnueabi//lib/../lib/crti.o crtbegin.o -L/usr/arm-linux-gnueabi//lib/../lib -L/usr/arm-linux-gnueabi//lib /tmp/helloworld-6b36a6.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed crtend.o /usr/arm-linux-gnueabi//lib/../lib/crtn.o

/usr/local/bin/ld: unrecognised emulation mode: armelf_linux_eabi

Supported emulations: elf_i386 i386linux elf32_x86_64 elf_x86_64 elf_l1om elf_k1om i386pep i386pe

clang-3.6: error: linker command failed with exit code 1 (use -v to see invocation)

This seems that linker is wrong, so I change the ld point to /usr/arm-linux-gnueabi/bin/ld

(using: ln -s /usr/arm-linux-gnueabi/bin/ld ld)

But I get anther question

Obfuscator-LLVM clang version 3.6.1 (tags/RELEASE_361/final) (based on Obfuscator-LLVM 3.6.1)

Target: arm--linux-gnueabi

Thread model: posix

 "/usr/local/bin/clang-3.6" -cc1 -triple armv4t--linux-gnueabi -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -main-file-name arm.c -mrelocation-model static -mthread-model posix -mdisable-fp-elim -fmath-errno -masm-verbose -mconstructor-aliases -target-cpu arm7tdmi -target-feature +soft-float-abi -target-abi aapcs-linux -mfloat-abi soft -v -dwarf-column-info -resource-dir /usr/local/bin/../lib/clang/3.6.1 -isysroot /usr/arm-linux-gnueabi/ -internal-isystem /usr/arm-linux-gnueabi//usr/local/include -internal-isystem /usr/local/bin/../lib/clang/3.6.1/include -internal-externc-isystem /usr/arm-linux-gnueabi//include -internal-externc-isystem /usr/arm-linux-gnueabi//usr/include -fdebug-compilation-dir /home/zyj/Desktop -ferror-limit 19 -fmessage-length 80 -mstackrealign -fno-signed-char -fobjc-runtime=gcc -fdiagnostics-show-option -fcolor-diagnostics -o /tmp/helloworld-fa5b7f.o -x c helloworld.c

clang -cc1 version 3.6.1 based upon Obfuscator-LLVM 3.6.1 default target i386-pc-linux-gnu

ignoring nonexistent directory "/usr/arm-linux-gnueabi//usr/local/include"

ignoring nonexistent directory "/usr/arm-linux-gnueabi//usr/include"

#include "..." search starts here:

#include <...> search starts here:

 /usr/local/bin/../lib/clang/3.6.1/include

 /usr/arm-linux-gnueabi//include

End of search list.

 "/usr/local/bin/ld" --sysroot=/usr/arm-linux-gnueabi/ -z relro -X --hash-style=gnu --build-id --eh-frame-hdr -m armelf_linux_eabi -dynamic-linker /lib/ld-linux.so.3 -o hello /usr/arm-linux-gnueabi//lib/../lib/crt1.o /usr/arm-linux-gnueabi//lib/../lib/crti.o crtbegin.o -L/usr/arm-linux-gnueabi//lib/../lib -L/usr/arm-linux-gnueabi//lib /tmp/helloworld-fa5b7f.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed crtend.o /usr/arm-linux-gnueabi//lib/../lib/crtn.o

/usr/local/bin/ld: cannot find crtbegin.o: No such file or directory

/usr/local/bin/ld: cannot find -lgcc

/usr/local/bin/ld: cannot find -lgcc_s

/usr/local/bin/ld: cannot find /usr/arm-linux-gnueabi/lib/libc.so.6 inside /usr/arm-linux-gnueabi/

/usr/local/bin/ld: cannot find /usr/arm-linux-gnueabi/lib/libc_nonshared.a inside /usr/arm-linux-gnueabi/

/usr/local/bin/ld: cannot find /usr/arm-linux-gnueabi/lib/ld-linux.so.3 inside /usr/arm-linux-gnueabi/

clang-3.6: error: linker command failed with exit code 1 (use -v to see invocation)

From above message I am confused about the:

/usr/local/bin/ld: cannot find crtbegin.o: No such file or directory

/usr/local/bin/ld: cannot find -lgcc

/usr/local/bin/ld: cannot find -lgcc_s

/usr/local/bin/ld: cannot find /usr/arm-linux-gnueabi/lib/libc.so.6 inside /usr/arm-linux-gnueabi/

/usr/local/bin/ld: cannot find /usr/arm-linux-gnueabi/lib/libc_nonshared.a inside /usr/arm-linux-gnueabi/

/usr/local/bin/ld: cannot find /usr/arm-linux-gnueabi/lib/ld-linux.so.3 inside /usr/arm-linux-gnueabi/

While all these lib is at the right location, why error says ld cannot find them.

If you need more imformation from me, please let me know.

Thanks

[Peter Smith via llvm-dev]

Hello,

Without going into too much detail I think the basic problem is that
when you use gcc as the linker driver you are using the linker from
aarch64-linux-gnu which will include the GNU linker supporting aarch64
and the aarch64 libraries. When you set the sysroot to
arm-linux-gnueabi you are using the aarch32 sysroot which won't
include the libraries and linker needed for aarch64. It will be worth
finding out the sysroot that aarch64-linux-gnu-gcc is using and use
that instead.

Peter

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[Richard Pennington via llvm-dev]

A simpler way might be to get ELLCC (http://ellcc.org):

rich@dev:~$ ~/ellcc/bin/ecc -target arm64v8-linux hello.c
rich@dev:~$ file a.out
a.out: ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), statically linked, not stripped
rich@dev:~$ ~/ellcc/bin/qemu-aarch64 a.out
hello world
rich@dev:~$

ELLCC includes all the stuff you need: libraries, linker, etc.

That was on an x86_64 system.

-Rich