For a school project, I have to implement a simple atomic_sub() function in
c. The implementation must use the asm() function.
Right now, my code looks like this
void atomic_sub( int * value, int dec_val) {
asm ("LOCK SUB (%0), %1;\n"
:
: "r" (value), "r" (dec_val)
: "memory");
}
The intention is for "value" to decrement by "dec_val" atomically, but when
I try to compile I get the following error.
"locking.c:28: Error: expecting lockable instruction after 'lock'"
This asm() call is on line 28, so this is the instruction the error is
referring to. Does anyone know why this isn't a lockable instruction?
According to the documentation from Intel I've read, a sub with a
destination of a memory address is lockable. Any ideas?
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