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

Wed Nov 2 02:52:12 PDT 2016

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

On 2 November 2016 at 07:49, via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 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
>
>
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