[Bug 1711337] Re: Firefox crashes at start on armv7L after 55.0.1 update

[James Donald]

Here is a working Firefox 59 deb package cross-compiled for 18.04 armhf:
https://www.dropbox.com/s/17ypog6btdq4wj7/firefox_59.0.1%2Bbuild1-0ubuntu1_armhf.deb?dl=0

I have installed and tested on RaspEX (Bionic armhf). I can also confirm
it works sandboxed on Ubuntu MATE Xenial and Raspbian Stretch. One way
to run on older systems is to unpack locally using ar + tar, download
libc6 and libstdc++6 bionic armhf debfiles and untar them as well, then
do:

  cd path/to/usr/lib/firefox
  LD_PRELOAD=path/to/usr/lib/arm-linux-gnueabihf/libstdc++.so.6:path/to/lib/arm-linux-gnueabihf/libm.so.6 \
    ./firefox

Cross-compiling via dpkg-buildpackage is fraught of issues, and similar
to what Chituc experienced the most difficult part was getting rustc to
properly cross-compile in all cases. I posted my main workaround for a
host/target header bug here: https://github.com/rust-lang-nursery/rust-
bindgen/issues/1229

To prevent the Skia misaligned instruction crash, I ended up editing
gfx/skia/generate_mozbuild.py to force SK_JUMPER_USE_ASSEMBLY to False.
However, there's stubborn code at the top of SkJumper.cpp that ends up
turning it on again so I had to override that too. Telling Skia to use
its non-asm fallback mode should be better than disabling Skia
altogether as we had for Firefox 57.

I tested some of our earlier theories too, and so far building Skia with
clang, everything with -thumb, -fstack-protector-strong, --enable-rust-
simd or other suggestions above do not seem to help at all with the Skia
SIGILL nor the strd r2, r3, [r1] SIGSEGV.

As for that strd r2, r3, [r1] crash, not much progress there aside from
our theory that it's in the XPCOM armhf-specific code. I'm merely
avoiding it by building in a 18.04 Docker container, but still no idea
why that works.

** Bug watch added: github.com/rust-lang-nursery/rust-bindgen/issues #1229
   https://github.com/rust-lang-nursery/rust-bindgen/issues/1229

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Title:
  Firefox crashes at start on armv7L after 55.0.1 update

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