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Jan Beulich
09c856316d
The "A" constraint, while documented up to gcc 4.5 as "The a and d registers, as a pair (for instructions that return half the result in one and half in the other)," never really behaved that (natural) way, but always meant (and is now also documented so) %eax _or_ %edx (%rax _or_ %rdx on x86-64) unless the operand was wide enough to require both (i.e. more than 32 bits on ix86 and more than 64 bits on x86-64). Interestingly something internal to the compiler changed between 4.4 and 4.5 to actually expose the difference - up to gcc 4.4 I was unable to construct a case where, when only the low half of the result is actually looked at, the result would be considered to be in %edx/%rdx (and %eax/%rax would be treated as unmodified by the instruction). Signed-off-by: Jan Beulich <jbeulich@suse.com> Acked-by: Keir Fraser <keir@xen.org> Tested-by: Don Slutz <dslutz@verizon.com>