Cross-compiling for ARMv6

[schwarzwalder93]

I am trying to cross-build Julia for ARMv6 with arm-buildroot-linux-uclibcgnueabi toolchain on a Intel-PC(x86) as a build machine.

What are the Makefile config parameters to be changed for such a cross-compilation ?

[nalimilan]

GitHub issues are not for questions, but for bug reports. I see you have also sent a message to the julia-dev mailing list, thus I'm closing this issue in favor of the latter. If you find actionable items that deserve a bug report, feel free to reopen it.

[ViralBShah]

I guess this is kind of an issue in the sense that we may need to figure out if this works, and if so, document it. In general, we do not have cross-compilation instructions.

[ihnorton]

There are cross-compile instructions in the windows readme. However,
bootstrapping the cross-compile binary requires Wine on linux. Maybe that
step could be run under QEMU user mode..

I guess this is kind of an issue in the sense that we may need to figure
out if this works, and if so, document it. Do we have cross-compilation
instructions?

—
Reply to this email directly or view it on GitHub
#10488 (comment).

[tkelman]

set XC_HOST to the prefix, and see what breaks first

[schwarzwalder93]

Here are some of the flags that I modified in Make.inc for the cross-compile:
OPENBLAS_TARGET_ARCH=ARMV6
OPENBLAS_DYNAMIC_ARCH = 1
ARCH=arm
XC_HOST = arm-buildroot-linux-uclibcgnueabi
HOSTCC = gcc
MARCH = armv6

And in deps/Makefile:
CONFIGURE_COMMON += --host=arm-buildroot-linux-uclibcgnueabi --target=arm-buildroot-linux-uclibcgnueabi

Now,its picking up the arm-buildroot-linux-uclibcgnueabi toolchain successfully.

1. I got errors in Tests/Checks target recipe for a few dependencies(Obvious,its testing the libs and exes on x86 platform),so I disabled them in makefiles.
2. LLVM build is not picking arm-buildroot-linux-uclibcgnueabi-strip instead it picks build machines stip and so llvm-install fails.How to resolve that ?
3. After skipping llvm-install,build breaks at FFTW, below is the log details

Making all in support
Making all in kernel
Making all in simd-support
Making all in dft
Making all in scalar
Making all in codelets
Making all in simd
Making all in common
Making all in sse2
Making all in avx
Making all in altivec
Making all in neon
libtool: compile: arm-buildroot-linux-uclibcgnueabi-gcc -march=armv6 -std=gnu99 -DHAVE_CONFIG_H -I. -I../../.. -I../../../kernel -I../../../dft -I../../../dft/simd -I../../../simd-support -mfpu=neon -O3 -fomit-frame-pointer -fstrict-aliasing -fno-schedule-insns -ffast-math -MT n1fv_2.lo -MD -MP -MF .deps/n1fv_2.Tpo -c n1fv_2.c -fPIC -DPIC -o .libs/n1fv_2.o
In file included from ../../../dft/simd/n1f.h:21:0,
from ../common/n1fv_2.c:71,
from n1fv_2.c:3:
../../../simd-support/simd-neon.h:33:2: error: #error "compiling simd-neon.h requires -mfpu=neon or equivalent"
#error "compiling simd-neon.h requires -mfpu=neon or equivalent"
^
In file included from ../../../simd-support/simd-neon.h:36:0,
from ../../../dft/simd/n1f.h:21,
from ../common/n1fv_2.c:71,
from n1fv_2.c:3:
/home/vish/work/ssdk/host/usr/lib/gcc/arm-buildroot-linux-uclibcgnueabi/4.8.3/include/arm_neon.h:32:2: error: #error You must enable NEON instructions (e.g. -mfloat-abi=softfp -mfpu=neon) to use arm_neon.h
#error You must enable NEON instructions (e.g. -mfloat-abi=softfp -mfpu=neon) to use arm_neon.h
^
In file included from ../../../dft/simd/n1f.h:21:0,
from ../common/n1fv_2.c:71,
from n1fv_2.c:3:
../../../simd-support/simd-neon.h:40:1: error: unknown type name 'float32x4_t'
typedef float32x4_t V;
^
../../../simd-support/simd-neon.h: In function 'LDA':
../../../simd-support/simd-neon.h:78:6: warning: implicit declaration of function 'vld1q_f32' [-Wimplicit-function-declaration]
return vld1q_f32((const float32_t *)x);
^
../../../simd-support/simd-neon.h:78:6: error: unknown type name 'float32_t'
../../../simd-support/simd-neon.h: In function 'LD':
../../../simd-support/simd-neon.h:84:6: warning: implicit declaration of function 'vcombine_f32' [-Wimplicit-function-declaration]
return vcombine_f32(vld1_f32((float32_t *)x), vld1_f32((float32_t *)(x + ivs)));
^
../../../simd-support/simd-neon.h:84:6: warning: implicit declaration of function 'vld1_f32' [-Wimplicit-function-declaration]
../../../simd-support/simd-neon.h:84:36: error: 'float32_t' undeclared (first use in this function)
return vcombine_f32(vld1_f32((float32_t *)x), vld1_f32((float32_t *)(x + ivs)));
^
../../../simd-support/simd-neon.h:84:36: note: each undeclared identifier is reported only once for each function it appears in
../../../simd-support/simd-neon.h:84:47: error: expected expression before ')' token
return vcombine_f32(vld1_f32((float32_t *)x), vld1_f32((float32_t *)(x + ivs)));
^
../../../simd-support/simd-neon.h:84:73: error: expected expression before ')' token
return vcombine_f32(vld1_f32((float32_t *)x), vld1_f32((float32_t *)(x + ivs)));
^
../../../simd-support/simd-neon.h: In function 'STA':
../../../simd-support/simd-neon.h:90:6: warning: implicit declaration of function 'vst1q_f32' [-Wimplicit-function-declaration]

Looks like some flags are missing in fftw configure,I tried adding but couldn't resolve..

[ViralBShah]

I would just do USE_SYSTEM_FFTW=1, since we have some known trouble with FFTW on ARM.

[ViralBShah]

@staticfloat Do you think we can have nightly dev PPAs for arm? They don't yet pass all tests, but people want to experiment - and this would be generally useful. Also, I am wondering if we should cross build for arm on travis and run a simple test suite just to get things started.

[staticfloat]

I enabled armhf a while back, but it appears the builds have been hanging because I was requiring patchelf for the build process. This is not available on ARM, so I've disabled it and we'll see how things go.

[ViralBShah]

@staticfloat Should we continue the PPA nightlies discussion in #8359 ?

@vishnusuganth Can you submit a PR? Many of these things can go into the existing ARM.inc, and can be enabled with a flag like make CROSS_COMPILE=1. This will generally be useful.

[schwarzwalder93]

@ViralBShah If I enable "USE_SYSTEM_XXX=1" flag ,should I build those libraries separately and add the path of the libXXX.so to LDFLAGS ?

[ViralBShah]

Usually, you would have them provided by the system - through apt-get or something similar. If they are on the system path, the julia build will pick them up.

[ViralBShah]

The other way to get around this is probably to remove the mention of --enable-neon in deps/Make.inc. There are other issues with FFTW and neon even if this builds:

FFTW/fftw3#30