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Fix atomic.h

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`=m` output operand means that value is write only, gcc may discard previous value because it assumes that it will be overwritten. This bug was not triggered in gcc v4 because `asm volatile` triggered full memory barrier.

With old version, this code will increase `markme` only by 2, not 3:
```
static int markme = 0;
markme++;
ATOMIC_BLOCK_NB(0xff) {
  ATOMIC_BARRIER(markme);  // markme is marked as overwritten, previous increment can be discarded
  markme++;
}
markme++;
```
This commit is contained in:
Petr Ledvina 2016-12-29 19:31:02 +01:00 • committed by borisbstyle
parent 46fa01a4b8
commit 108d9d6b61
1 changed files with 1 additions and 1 deletions
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2
src/main/build/atomic.h
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@ -104,7 +104,7 @@ static inline uint8_t __basepriSetRetVal(uint8_t prio)
__asm__ volatile ("\t# barier(" #data ") end\n" : : "m" (**__d)); \
} \
typeof(data) __attribute__((__cleanup__(__UNIQL(__barrierEnd)))) *__UNIQL(__barrier) = &data; \
__asm__ volatile ("\t# barier (" #data ") start\n" : "=m" (*__UNIQL(__barrier)))
__asm__ volatile ("\t# barier (" #data ") start\n" : "+m" (*__UNIQL(__barrier)))
// define these wrappers for atomic operations, use gcc buildins