On Thu, Oct 22, 2020 at 11:36:40AM +0200, David Hildenbrand wrote: > On 22.10.20 11:32, David Laight wrote: > > From: David Hildenbrand > >> Sent: 22 October 2020 10:25 > > ... > >> ... especially because I recall that clang and gcc behave slightly > >> differently: > >> > >> https://github.com/hjl-tools/x86-psABI/issues/2 > >> > >> "Function args are different: narrow types are sign or zero extended to > >> 32 bits, depending on their type. clang depends on this for incoming > >> args, but gcc doesn't make that assumption. But both compilers do it > >> when calling, so gcc code can call clang code. > > > > It really is best to use 'int' (or even 'long') for all numeric > > arguments (and results) regardless of the domain of the value. > > > > Related, I've always worried about 'bool'.... > > > >> The upper 32 bits of registers are always undefined garbage for types > >> smaller than 64 bits." > > > > On x86-64 the high bits are zeroed by all 32bit loads. > > Yeah, but does not help here. > > > My thinking: if the compiler that calls import_iovec() has garbage in > the upper 32 bit > > a) gcc will zero it out and not rely on it being zero. > b) clang will not zero it out, assuming it is zero. > > But > > a) will zero it out when calling the !inlined variant > b) clang will zero it out when calling the !inlined variant > > When inlining, b) strikes. We access garbage. That would mean that we > have calling code that's not generated by clang/gcc IIUC. > > We can test easily by changing the parameters instead of adding an "inline". Let me try that as well, as I seem to have a good reproducer, but it takes a while to run... greg k-h
