ARM cross-compile does not use v8 snapshots

[orangemocha]

nodejs/node#3962 enabled snapshots in Node however this doesn't seem to work with the ARM cross-compiler, as seen in https://ci.nodejs.org/job/node-cross-compile/588/nodes=cross-compiler-pi1p/console

/home/iojs/build/workspace/node-cross-compile/nodes/cross-compiler-pi1p/out/Release/mksnapshot: 1: /home/iojs/build/workspace/node-cross-compile/nodes/cross-compiler-pi1p/out/Release/mksnapshot: Syntax error: word unexpected (expecting ")")

I changed the node-cross-compile to pass --without-snapshot to configure, so that we can continue running CI while we figure the best long-term approach.

A few questions:

1. Is it absolutely impossible to produce a snapshot on the build platform, if it's different from the target platform? Or is it just a limitation in the compiler?
2. Are ARM release builds coming out of the cross-compile job?
3. Can we live without snapshots for ARM?

/cc @nodejs/build

[bnoordhuis]

Is it absolutely impossible to produce a snapshot on the build platform, if it's different from the target platform?

Only if you have an emulator. What the snapshot does is compile and execute JS to native machine code, then save the generated machine code to an image.

[indutny]

qemu?

[indutny]

Also a question how does V8 handle this? I'm sure that Google cross-compiles it for arm. cc @ofrobots

[targos]

There is some documentation about this here: https://github.com/v8/v8/wiki/Cross-compiling%20for%20ARM

[indutny]

@targos I'm afraid that this page is very likely to be outdated. V8 does not use scons for a very long time now.

[indutny]

@orangemocha is there any way to check that want_separate_host_toolset was 1 during our builds?

[indutny]

It looks like it was 0. This is very likely a cause of the problem.

[indutny]

Wait, are we cross-compiling there? Or is it an actual raspberry pi?

[ofrobots]

Looking output:

Building remotely on node-msft-cross-compiler-1 (cross-compiler-pi1p) in workspace /home/iojs/build/workspace/node-cross-compile/nodes/cross-compiler-pi1p

The job ran on https://ci.nodejs.org/computer/node-msft-cross-compiler-1/ which is described as "Ubuntu 14.04 LTS with Raspberry Pi cross compiler installed", so I would say this is a cross-compilation.

[indutny]

This is a config.gypi:

{ 'target_defaults': { 'cflags': [],
                       'default_configuration': 'Release',
                       'defines': [],
                       'include_dirs': [],
                       'libraries': []},
  'variables': { 'arm_float_abi': 'hard',
                 'arm_fpu': 'vfpv2',
                 'arm_thumb': 0,
                 'arm_version': '6',
                 'asan': 0,
                 'gas_version': '2.24',
                 'host_arch': 'arm',
                 'icu_small': 'false',
                 'node_byteorder': 'little',
                 'node_install_npm': 'true',
                 'node_prefix': '/usr/local',
                 'node_release_urlbase': '',
                 'node_shared_http_parser': 'false',
                 'node_shared_libuv': 'false',
                 'node_shared_openssl': 'false',
                 'node_shared_zlib': 'false',
                 'node_tag': '',
                 'node_use_dtrace': 'false',
                 'node_use_etw': 'false',
                 'node_use_lttng': 'false',
                 'node_use_openssl': 'true',
                 'node_use_perfctr': 'false',
                 'openssl_fips': '',
                 'openssl_no_asm': 0,
                 'python': '/usr/bin/python',
                 'target_arch': 'arm',
                 'uv_parent_path': '/deps/uv/',
                 'uv_use_dtrace': 'false',
                 'v8_enable_gdbjit': 0,
                 'v8_enable_i18n_support': 0,
                 'v8_no_strict_aliasing': 1,
                 'v8_optimized_debug': 0,
                 'v8_random_seed': 0,
                 'v8_use_snapshot': 'true',
                 'want_separate_host_toolset': 0}}

For some reason host_arch is arm there...

[ofrobots]

Indeed. Odd.

[orangemocha]

Definitely cross-compiling. Better get the nitty gritty details from @joaocgreis, who set this up and also did some experiments with qemu.

[ofrobots]

I think @indutny might be right. The job seem to be doing a configure instead of configure --dest-cpu=arm. On my x64 box, this is the config.gypi I get:

lemongrab :: ~/src/node ‹master› % ./configure --dest-cpu=arm
creating  ./icu_config.gypi
{ 'target_defaults': { 'cflags': [],
                       'default_configuration': 'Release',
                       'defines': [],
                       'include_dirs': [],
                       'libraries': []},
  'variables': { 'arm_float_abi': 'default',
                 'arm_fpu': 'vfpv2',
                 'arm_thumb': 0,
                 'arm_version': 'default',
                 'asan': 0,
                 'gas_version': '2.24',
                 'host_arch': 'x64',
                 'icu_small': 'false',
                 'node_byteorder': 'little',
                 'node_install_npm': 'true',
                 'node_prefix': '/usr/local',
                 'node_release_urlbase': '',
                 'node_shared_http_parser': 'false',
                 'node_shared_libuv': 'false',
                 'node_shared_openssl': 'false',
                 'node_shared_zlib': 'false',
                 'node_tag': '',
                 'node_use_dtrace': 'false',
                 'node_use_etw': 'false',
                 'node_use_lttng': 'false',
                 'node_use_openssl': 'true',
                 'node_use_perfctr': 'false',
                 'openssl_fips': '',
                 'openssl_no_asm': 0,
                 'python': '/usr/bin/python',
                 'target_arch': 'arm',
                 'uv_parent_path': '/deps/uv/',
                 'uv_use_dtrace': 'false',
                 'v8_enable_gdbjit': 0,
                 'v8_enable_i18n_support': 0,
                 'v8_no_strict_aliasing': 1,
                 'v8_optimized_debug': 0,
                 'v8_random_seed': 0,
                 'v8_use_snapshot': 'true',
                 'want_separate_host_toolset': 1}}

[joaocgreis]

I believe I have this working now and will be able to re-enable snapshots when nodejs/node#4117 lands. V8 can handle cross compiling of snapshots if the {CC,CXX}_host variables are defined, by compiling the mksnapshot executable with the host compiler.

[joaocgreis]

nodejs/node#4117 has landed and CI is building snapshots for arm now: https://ci.nodejs.org/job/node-test-commit-arm-fanned/768/ . I will close this for now, please reopen if there are issues.