* Brian Gerst <brgerst@xxxxxxxxx> wrote: > > Ok, so your goal is to allow the x32 ABI, but not 32-bit user-space? > > It just seems odd that x32 (which is really a 64-bit ABI with 32-bit pointers) > depended on enabling 32-bit support. Other than both using the core compat > code, they are not really related. Yeah. > > I suppose that makes some sense, it might be a valid 'attack surface > > reduction' technique, while still allowing the x32 ABI. > > > > But I'm not sure we should bother and complicate things: 32-bit compat isn't > > going away anytime soon, and most of CONFIG_COMPAT is needed for x32. > > Many of the compat syscalls are unused by x32. It only needs to handle syscalls > with pointers embedded in data structures differently than native 64-bit. Yeah, but in fact those are the 'most interesting' (read: most complex) aspects of the generic compat machinery. So most of the 'core compat' functionality is used - even though we don't use many of the (trivial) argument-converted syscall variants. > 64-bit integer arguments (ie., loff_t) do not need special handling, since they > can be passed in a single register instead of a pair of 32-bit registers. This > won't solve that particular issue yet, but it's something to be aware of for > future cleanups. Yes, and I think 'X32' is a misnomer in that sense: in reality it's a 90% 64-bit ABI that just happens to have a handful of additional system calls that can deal with data pointers truncated to 32 bits. So 'C64' would have been a better name: a compacted 64-bit ABI - but that particular name has its own problems ;-) Maybe S64 (small 64-bit memory model)? 'S64' would also have been an easier sell to distros: they generally resist adding anything that smells old, 32-bit ... but kernel hackers and marketing were always somewhat disjunct sets ;-) I'm wondering whether we'll ever see a 48-bit user-space pointer model ;-) They are misaligned by 32 bits, but x86 CPUs generally handle 32-bit misalignment just fine. The killer would be to zero-extend from 48 bits to 64 bits I suspect - there's no natural instruction for that. > > So maybe we could introduce CONFIG_X86_32_ABI=y or so, which would cover just > > the 32-bit entry code and the signal frame compatibility layer? > > Yes. Ok, then it sounds good to me! Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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