TechFindings

Update 2015-10-11:See separate post for Node version 4 for different OpenWrt targets. Information about v4 added below.

I managed to build (and run) Node.js OpenWrt and my Archer C20i with a MIPS 24K Little Endian CPU, without FPU (target=ramips/mt7620).

Node.js v0.10.40
First edit (set to false):

deps/v8/build/common.gypi

    54      # Similar to vfp but on MIPS.
    55      'v8_can_use_fpu_instructions%': 'false',
   
    63      # Similar to the ARM hard float ABI but on MIPS.
    64      'v8_use_mips_abi_hardfloat%': 'false',

For 15.05 I use this script to run configure:

#!/bin/sh -e

#Tools
export CSTOOLS="$STAGING_DIR"
export CSTOOLS_INC=${CSTOOLS}/include
export CSTOOLS_LIB=${CSTOOLS}/lib

export CC="mipsel-openwrt-linux-uclibc-gcc"
export CXX="mipsel-openwrt-linux-uclibc-g++"
export LD="mipsel-openwrt-linux-uclibc-ld"

export CFLAGS="-isystem${CSTOOLS_INC}"
export CPPFLAGS="-isystem${CSTOOLS_INC}"

export PATH="${CSTOOLS}/bin:$PATH"

./configure --without-snapshot --dest-cpu=mipsel --dest-os=linux --without-npm

bash --norc

Then just “make”. I have uploaded the compiled binary node to DropBox.

Compilation for (DD) trunk (with musl rather than uclibc) fails for v0.10.40.

Node.js v4.1.2
Node.js v4 does not run without a FPU. Normally Linux emulates an FPU if it is not present, but this feature is disabled in OpenWRT. I built and published r47168 with FPU emulation and Node v4.1.2.

Node.js 4.1.2 is configured like:

#!/bin/sh -e

#Tools
export CSTOOLS="$STAGING_DIR"
export CSTOOLS_INC=${CSTOOLS}/include
export CSTOOLS_LIB=${CSTOOLS}/lib

export CC="mipsel-openwrt-linux-musl-gcc"
export CXX="mipsel-openwrt-linux-musl-g++"
export LD="mipsel-openwrt-linux-musl-ld"

export CFLAGS="-isystem${CSTOOLS_INC}"
export CPPFLAGS="-isystem${CSTOOLS_INC}"

export PATH="${CSTOOLS}/bin:$PATH"

./configure --without-snapshot --dest-cpu=mipsel --dest-os=linux --without-npm --with-mips-float-abi=soft

bash --norc

Dependencies
In order to run the node binary on OpenWrt you need to install:

# opkg update
# opkg install librt
# opkg install libstdcpp

Performance
The 64MB or RAM of my Archer C20i is not sufficient to run octane-benchmark (even if the node binary and the benchmark are stored on a USB drive). However, I have a Mandelbrot benchmark that I can run. For Archer C20i, timings are:

C/Soft Float                     48s
Lua                              82s
Node.js v0.10.40 (soft float)    65s
Node.js v4.1.2 (FPU emulation)  444s (63s user, 381s kernel)

Clearly, the OpenWrt developers have a good reason to leave FPU emulation out. However, for Node.js in the future, FPU emulation seems to be the only way. My Mandelbrot benchmark is of course ridiculously dependent on FPU performance. For more normal usage, perhaps the penalty is less significant.

Other MIPS?
The only other MIPS I have had the opportunity to try was my WDR3600, a Big Endian 74K. It does not work:

• v0.10.38 does not build at all (big endian MIPS seems unsupported)
• v0.12.* builds, but it does not run (floating point exceptions), despite I managed to build for Soft Float.

I need to try rebuilding OpenWRT with FPU emulation for ar71xx, then perhaps Node.js v4 will work.