On Wed, Apr 1, 2015 at 1:52 PM, Denys Vlasenko <dvlas...@redhat.com> wrote: > > BTW, AMD64 docs do explicitly say that MOVs from segment registers > to gpregs are zero-extending.
Yeah, I think anything even *remotely* recent enough to do 64-bit does zero-extending. Even on the 32-bit side, anything that does register renaming is much better off with zero-extension than with partial register writes. And I found the "push" thing. It's actually documented: "When pushing a segment selector onto the stack, the Pentium 4, Intel Xeon, P6 family, and Intel486 processors decrement the ESP register by the operand size and then write 2 bytes. If the operand size is 32-bits, the upper two bytes of the write are not modified" but I can't find any similar documentation for the "mov Sreg->register" thing. So now I'm starting to doubt my own memory. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/