[Also looping in bug-gnulib] On Tue, Feb 03, 2015 at 11:30:17AM -0500, Carlos O'Donell wrote: > Is this a valgrind bug, false positive in valgrind, or bug in glibc? > > It clearly says we have a move that depends on an uninitizlied value, > so something read the value and tried to do something with it.
It is a combination of multiple things actually. The uninitialized value here is the padding in the structure and we have fixed such warnings in the past; see the nscd stats warning[1] for example. This warning doesn't trigger on x86 though due to the code that gcc generates for it - it explicitly ANDs the bit field in the struct before testing it. On s390, the optimizer does away with the AND operation and tests the entire thing for some reason - I haven't figured out why but the instruction combiner RTL pass does away with the AND operation. This is also why I started out filing a gcc bug, but then changed my mind and fixed it in glibc instead, since I presumed that the compiler can assume that the padding is also appropriately initialized. But then, I am not completely sure if the compiler is allowed to make that assumption. Siddhesh
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