AAPCS requires stack pointers to be aligned on a double word boundary.
In addition, Clang-3.6 assumes the stack pointer is always aligned to
a 8 byte boundary upon function entry, at least in armv7-m, causing
hard-to-find errors in the compiled code.
- Move generic implementation of atomic_set_return to core/atomic.c
- Generic implementation of atomic compare and swap in core/atomic.c
- atomic_cas is used to implement atomic counters in core/include/atomic.h
- atomic_int_t is an atomic integer type
- ATOMIC_INIT can be used as an initializer for atomic_int_t
- ATOMIC_VALUE gets a reference to the value of an atomic integer
Clang 3.6 is stricter than GCC and previous releases of Clang regarding
naked functions and now only allows inline asm inside naked functions.
This is a refactoring of the functions isr_pendsv, isr_svc,
context_save, context_restore to still be naked functions but allow
building with Clang 3.6
- removed the __attribute__((naked)) from ISRs
- removed ISR_ENTER() and ISR_EXIT() macros
Rationale: Cortex-Mx MCUs save registers R0-R4 automatically
on calling ISRs. The naked attribute tells the compiler not
to save any other registers. This is fine, as long as the
code in the ISR is not nested. If nested, it will use also
R4 and R5, which will then lead to currupted registers on
exit of the ISR. Removing the naked will fix this.
