I notice that _q_value is referenced twice in the constraints.
Can we get rid of the reference causing the problem, i.e.:
asm volatile("0:\n"
"ldrex %[newValue], [%[_q_value]]\n"
"sub %[newValue], %[newValue], #1\n"
"strex %[result], %[newValue], [%[_q_value]]\n"
"teq %[result], #0\n"
"bne 0b\n"
: [newValue] "=&r" (newValue),
[result] "=&r" (result),
: [_q_value] "r" (&_q_value)
: "cc", "memory");
My understanding is that the "memory" clobber is enough to warn the
compiler that that _q_value might be modified ... though I'm not a tool
expert so I could be wrong there.
Alternatively, remove both constraints and just use "Q" instead. If
we're actually using the constraint in instructions, "m" is wrong
because we can't handle pre/post increment/decrement addressing, and no
offset is allowed in ARM so "o" wouldn't be correct either:
asm volatile("0:\n"
"ldrex %[newValue], %[_q_value]\n"
"sub %[newValue], %[newValue], #1\n"
"strex %[result], %[newValue], %[_q_value]\n"
"teq %[result], #0\n"
"bne 0b\n"
: [newValue] "=&r" (newValue),
[_q_value] "+Q" (_q_value),
[result] "=&r" (result),
:: "cc", "memory");
I don't have a suitable toolchain to test this with right now, though...
can someone else see if it makes any difference?
--
volatile int causes inline assembly build failure
https://bugs.launchpad.net/bugs/675347
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