Work around a kernel bug on Android.

Work around a kernel bug on Android.

Kernel does not clear If-Then execution state bits when entering ARM signal handler which violates requirements imposed by ARM architecture reference. Some CPUs look at these bits even while in ARM mode which causes them
to skip some instructions in the prologue of the signal handler.

To work around the issue we insert enough NOPs in the prologue to ensure that no actual instructions are skipped and then branch to the actual signal handler.

For the kernel patch that fixes the issue see: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=6ecf830e5029598732e04067e325d946097519cb

This causes sporadic crashes with SIGILL on some testing devices (e.g. Nexus 7).

R=fschneider@google.com
BUG=

Committed: https://github.com/dart-lang/sdk/commit/b089d4f0040cb02596c33ffecbee2c7dc95bc108

[Florian Schneider, 2016-05-02 13:44:45]

https://codereview.chromium.org/1940883002/diff/1/runtime/vm/thread_interrupt...
File runtime/vm/thread_interrupter_android.cc (right):

https://codereview.chromium.org/1940883002/diff/1/runtime/vm/thread_interrupt...
runtime/vm/thread_interrupter_android.cc:71: asm volatile("bx %3"
Need this only on ARM, not on Android ia32 for example.

[Vyacheslav Egorov (Google), 2016-05-02 14:05:41]

PTAL

[Florian Schneider, 2016-05-02 14:43:43]

Lgtm.

https://codereview.chromium.org/1940883002/diff/20001/runtime/vm/signal_handl...
File runtime/vm/signal_handler.h (right):

https://codereview.chromium.org/1940883002/diff/20001/runtime/vm/signal_handl...
runtime/vm/signal_handler.h:43: #if defined(HOST_ARCH_ARM) && \
s/HOST_ARCH_ARM/TARGET_ARCH_ARM/

[zra, 2016-05-02 15:53:53]

zra@google.com changed reviewers:
+ zra@google.com

[zra, 2016-05-02 15:53:54]

DBC

As an alternative to this fix, would it also work to compile the VM with
-mthumb? That is how Flutter/Mojo are building the VM anyway. Maybe we should do
the same with the standalone VM.

https://codereview.chromium.org/1940883002/diff/20001/runtime/vm/signal_handl...
File runtime/vm/signal_handler.h (right):

https://codereview.chromium.org/1940883002/diff/20001/runtime/vm/signal_handl...
runtime/vm/signal_handler.h:43: #if defined(HOST_ARCH_ARM) && \
On 2016/05/02 14:43:43, Florian Schneider wrote:
> s/HOST_ARCH_ARM/TARGET_ARCH_ARM/

I think HOST might be right since we don't want this code in simarm.

[Vyacheslav Egorov (Google), 2016-05-02 17:12:51]

Description was changed from

==========
Work around a kernel bug on Android.

Kernel does not clear If-Then execution state bits when entering ARM signal
handler which violates requirements imposed by ARM architecture reference. Some
CPUs look at these bits even while in ARM mode which causes them
to skip some instructions in the prologue of the signal handler.

To work around the issue we insert enough NOPs in the prologue to ensure that no
actual instructions are skipped and then branch to the actual signal handler.

For the kernel patch that fixes the issue see:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=6ec...

This causes sporadic crashes with SIGILL on some testing devices (e.g. Nexus 7).

R=fschneider@google.com
BUG=
==========

to

==========
Work around a kernel bug on Android.

Kernel does not clear If-Then execution state bits when entering ARM signal
handler which violates requirements imposed by ARM architecture reference. Some
CPUs look at these bits even while in ARM mode which causes them
to skip some instructions in the prologue of the signal handler.

To work around the issue we insert enough NOPs in the prologue to ensure that no
actual instructions are skipped and then branch to the actual signal handler.

For the kernel patch that fixes the issue see:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=6ec...

This causes sporadic crashes with SIGILL on some testing devices (e.g. Nexus 7).

R=fschneider@google.com
BUG=

Committed:
https://github.com/dart-lang/sdk/commit/b089d4f0040cb02596c33ffecbee2c7dc95bc108
==========

[Vyacheslav Egorov (Google), 2016-05-02 17:12:52]

Committed patchset #2 (id:20001) manually as
b089d4f0040cb02596c33ffecbee2c7dc95bc108 (presubmit successful).