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The output constraint specifies an x86 register (EAX), which is impossible on an arm cpu. Also, the lock prefix is platform-specific to x86, and the decl and setnz instructions are not supported on arm as well.
This is the output constraint:
: "=a" (nz)
It is telling gcc to use the register eax to hold the result and then copy it to the variable nz.
于 2012-07-25T16:10:45.927 回答