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Andy Ross 668bb3cb22 lib/os/heap: Compiler bug workaround on ARC
This is a workaround for a compiler bug on (at least) GCC 12.1.0 in
Zephyr SDK 0.15.1.  The optimizer generates this function with a last
instruction that is an unconditional branch (a tail call into the
chunk_set() handling).  But that means that the NEXT instruction gets
decoded as part of the branch delay slot, but that instruction isn't
part of this function!  Some instructions aren't legal in branch delay
slots.  One of those is ENTER_S, which is a very common entry
instruction for whatever function the linker places after us.  It
seems like the compiler doesn't understand this problem.  Stuff a NOP
in to guarantee the code is legal.

Comment above is duplicated in the code.  The workaround is
straightforward once the issue is understood, but the path to get here
was hilariously weird.

Fixes #54720

Signed-off-by: Andy Ross <andyross@google.com>
2023-02-10 14:32:26 -05:00
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The Zephyr Project is a scalable real-time operating system (RTOS) supporting
multiple hardware architectures, optimized for resource constrained devices,
and built with security in mind.

The Zephyr OS is based on a small-footprint kernel designed for use on
resource-constrained systems: from simple embedded environmental sensors and
LED wearables to sophisticated smart watches and IoT wireless gateways.

The Zephyr kernel supports multiple architectures, including ARM (Cortex-A,
Cortex-R, Cortex-M), Intel x86, ARC, Nios II, Tensilica Xtensa, and RISC-V,
SPARC, MIPS, and a large number of `supported boards`_.

.. below included in doc/introduction/introduction.rst


Getting Started
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Welcome to Zephyr! See the `Introduction to Zephyr`_ for a high-level overview,
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.. _Discord Invite: https://chat.zephyrproject.org
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.. _Introduction to Zephyr: http://docs.zephyrproject.org/latest/introduction/index.html
.. _Getting Started Guide: http://docs.zephyrproject.org/latest/develop/getting_started/index.html
.. _Contribution Guide: http://docs.zephyrproject.org/latest/contribute/index.html
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.. _Security: http://docs.zephyrproject.org/latest/security/index.html
.. _Asking for Help Tips: https://docs.zephyrproject.org/latest/develop/getting_started/index.html#asking-for-help