On Tue, Sep 10, 2013 at 07:29:51AM -0700, Matthew Fleming wrote: > I don't know exactly what the stock malloc(9) will return, but memguard(9), > under its default mode with vm.memguard.options having MG_GUARD_AROUND set > will align the returned pointer to only 16 bytes. When I added that > feature I almost made it 8 bytes, but I think I saw that uma(9) had a > 16-byte alignment so I preserved that. I.e., this code does still work > with malloc(9) and memguard(9). > > But why does this need 16 byte alignment? Especially when one of the > comments says 4-byte alignment?
The comment about 4-byte alignment is for VIA. For Intel, citing the IA-32 SDM rev. 47, Vol.3, 9.11.6 Microcode Update Loader: "The microcode update data requires a 16-byte boundary alignment". I.e. CPU takes the linear address of the buffer, which must be aligned on 16 bytes.
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