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Diffstat (limited to 'open_issues/64-bit_port.mdwn')
| -rw-r--r-- | open_issues/64-bit_port.mdwn | 80 |
1 files changed, 80 insertions, 0 deletions
diff --git a/open_issues/64-bit_port.mdwn b/open_issues/64-bit_port.mdwn index 2d273ba1..66da44b9 100644 --- a/open_issues/64-bit_port.mdwn +++ b/open_issues/64-bit_port.mdwn @@ -57,3 +57,83 @@ the [[microkernel/mach/gnumach/ports/Xen]] platform. and switching to long mode, then jumping to c code to complete the initialization <braunr> i think i'll go the second way with x15, so you'll have the two :) + + +# IRC, freenode, #hurd, 2012-12-12 + +In context of [[microkernel/mach/gnumach/memory_management]]. + + <tschwinge> Or with a 64-bit one? ;-P + <braunr> tschwinge: i think we all had that idea in mind :) + <pinotree> tschwinge: patches welcome :P + <youpi> tschwinge: sure, please help us settle down with the mig stuff + <youpi> what was blocking me was just deciding how to do it + <braunr> hum, what's blocking x86_64, except time to work on it ? + <youpi> deciding the mig types & such things + <youpi> i.e. the RPC ABI + <braunr> ok + <braunr> easy answer: keep it the same + <youpi> sorry, let me rephrase + <youpi> decide what ABI is supposed to be on a 64bit system, so as to know + which way to rewrite the types of the kernel MIG part to support 64/32 + conversion + <braunr> can't this be done in two steps ? + <youpi> well, it'd mean revamping the whole kernel twice + <youpi> as the types at stake are referenced in the whole RPC code + <braunr> the first step i imagine would simply imply having an x86_64 + kernel for 32-bits userspace, without any type change (unless restricting + to 32-bits when a type is automatically enlarged on 64-bits) + <youpi> it's not so simple + <youpi> the RPC code is tricky + <youpi> and there are alignments things that RPC code uses + <youpi> which become different when build with a 64bit compiler + <pinotree> there are also things like int[N] for io_stat_struct and so on + <braunr> i see + <youpi> making the code wrong for 32 + <youpi> thus having to change the types + <youpi> pinotree: yes + <pinotree> (doesn't mig support structs, or it is too clumsy to be used in + practice?) + <braunr> pinotree: what's the problem with that (i explcitely said changing + int to e.g. int32_t) + <youpi> that won't fly for some of the calls + <youpi> e.g. getting a thread state + <braunr> pinotree: no it doesn't support struct + <pinotree> braunr: that some types in struct stat are long, for instance + <braunr> pinotree: same thing with longs + <braunr> youpi: why wouldn't it ? + <youpi> that wouldn't work on a 64bit system + <youpi> so we can't make it int32_t in the interface definition + <braunr> i understand the alignment issues and that the mig code adjusts + the generated code, but not the content of what is transfered + <braunr> well of course + <braunr> i'm talking about the first step here + <braunr> which targets a 32-bits userspace only + <youpi> ok, so we agree + <youpi> the second step would have to revamp the whole RPC code again + <braunr> i imagine the first to be less costly + <braunr> well, actually no + <braunr> you're right, the mig stuff would be easy on the application side, + but more complicated on the kernel side, since it would really mean + dealing with 64-bits values there + <braunr> (unless we keep a 3/1 split instead of giving the full 4g to + applications) + +See also [[microkernel/mach/gnumach/memory_management]]. + + <youpi> (I don't see what that changes) + <braunr> if the kernel still runs with 32-bits addresses, everything it + recevies from or sends through mig can be stored with the user side + 32-bits types + <youpi> err, ok, but what's the point of the 64bit kernel then ? :) + <braunr> and it simply uses 64-bits addresses to deal with physical memory + <youpi> ok + <youpi> that could even be a 3.5/0.5 split then + <braunr> but the memory model forces us to run either at the low 2g or the + highest ones + <youpi> but linux has 3/1, so we don't need that + <braunr> otherwise we need an mcmodel=medium + <braunr> we could do with mcmodel=medium though, for a time + <braunr> hm actually no, it would require mcmodel=large + <braunr> hum, that's stupid, we can make the kernel run at -2g, and use 3g + up to the sign extension hole for the kernel map |