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impossible constraint in asm
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impossible constraint in asm


  • Subject: impossible constraint in asm
  • From: "Steve Jenson" <email@hidden>
  • Date: Mon, 6 Oct 2008 18:36:22 -0700

Hi,

I've inherited a chunk of code and am trying to get it to compile on
Leopard but am running into a problem and I'm hoping somebody on this
list has seen it before.

typedef uint32_t lockStructure;
static inline int __compareAndSwap(lockStructure *ptr, lockStructure
old, lockStructure new) {
  lockStructure prev = old;
  asm volatile("lock cmpxchgl %1,%2" : "=a" (old) : "q" (new), "m"
(*ptr),"0" (old) : "memory");
  return old != prev;
}

When I try to compile this, I get the following error for the line
starting with asm:

error: impossible constraint in 'asm'

This isn't with Xcode but instead with a standard Makefile. I'm using
the stock gcc 4.0.1 that comes with the latest Xcode.

Thanks,
Steve
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