5a4b65ab50
GCC 4.6 explicitly represents the MDR register. It may be accessed via the "z" constraint. Perhaps more importantly, it tracks when the MDR register is clobbered and uses the RETF instruction if the incoming value is still valid. Thus it is important to (at least) clobber the MDR register in relevant inline assembly fragments, lest RETF be used incorrectly. The only instances I could find are here. There are reads of the MDR register in kernel/gdb-stub.c, but that's harmless. Although, frankly, __builtin_return_address(0) might be a better thing in those cases. Certainly MDR isn't going to contain anything else that might be useful... Signed-off-by: Richard Henderson <rth@redhat.com> Signed-off-by: David Howells <dhowells@redhat.com> |
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