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diff --git a/open_issues/arm_port.mdwn b/open_issues/arm_port.mdwn new file mode 100644 index 00000000..26e0b770 --- /dev/null +++ b/open_issues/arm_port.mdwn @@ -0,0 +1,267 @@ +[[!meta copyright="Copyright © 2012, 2013, 2014 Free Software Foundation, +Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +Several people have expressed interested in a port of GNU/Hurd for the ARM +architecture. + + +# IRC, freenode, #hurd, 2012-07-28 + + <mcsim> Has anyone heard about porting hurd and gnu/mach to arm + architecture? + <braunr> mcsim: i think so + <braunr> mcsim: why are you asking ? + <mcsim> I found an article where author stated that he has ported hurd to + arm, but I have never met this information before. + <mcsim> He wrote ethernet driver and managed to use ping command + <mcsim> author's name is Sartakov Vasily + <braunr> well that's possible, a long time ago + <braunr> and it was probably not complete enough to be merged upstream + <braunr> like many other attempts at many other things + <mcsim> Not so long. Article is dated by June 2011. + <braunr> do you have a link ? + <mcsim> Yes, but it is in Russian. + <braunr> oh + <braunr> well i don't remember him sharing that with us + <antrik> mcsim: he did some work on porting Mach, but AIUI never got it + nearly finished + <antrik> nowadays he does L4 stuff + <antrik> was also at FOSDEM + + +## IRC, freenode, #hurd, 2012-10-09 + + <mcsim> bootinfdsds: There was an unfinished port to arm, if you're + interested. + <tschwinge> mcsim: Has that ever been published? + <mcsim> tschwinge: I don't think so. But I have an email of that person and + I think that this could be discussed with him. + + +## IRC, freenode, #hurd, 2012-10-10 + + <tschwinge> mcsim: If you have a contact to the ARM porter, could you + please ask him to post what he has? + <antrik> tschwinge: we all have the "contact" -- let me remind you that he + posted his questions to the list... + + +## IRC, freenode, #hurd, 2012-10-17 + + <mcsim> tschwinge: Hello. The person who I wrote regarding arm port of + gnumach still hasn't answered. And I don't think that he is going to + answer. + + +# IRC, freenode, #hurd, 2012-11-15 + + <matty3269> Well, I have a big interest in the ARM architecture, I worked + at ARM for a bit too, and I've written my own little OS that runs on + qemu. Is there an interest in getting hurd running on ARM? + <braunr> matty3269: not really currently + <braunr> but if that's what you want to do, sure + <tschwinge> matty3269: Well, interest -- sure!, but we don't really have + people savvy in low-level kernel implementation on ARM. I do know some + bits about it, but more about the instruction set than about its memory + architecture, for example. + <tschwinge> matty3269: But if you're feeling adventurous, by all means work + on it, and we'll try to help as we can. + <tschwinge> matty3269: There has been one previous attempt for an ARM port, + but that person never published his code, and apparently moved to a + different project. + <tschwinge> matty3269: I can help with toolchains (GCC, etc.) things for + ARM, if there's need. + <matty3269> tschwinge: That sounds great, thanks! Where would you recommend + I start (at the moment I've got Mach checked out and am trying to get it + compiled for i386) + <matty3269> I'm guessing that the Mach micro-kernel is all that would need + to be ported or are there arch-dependant bits of code in the server + processes? + <tschwinge> matty3269: + http://www.gnu.org/software/hurd/faq/system_port.html has some + information. Mach is the biggest part, yes. Then some bits in glibc and + libpthread, and even less in the Hurd libraries and servers. + <tschwinge> matty3269: Basically, you'd need equivalents for the i386 (and + similar) directories, yep. + <tschwinge> Though, you may be able to avoid some cruft in there. + <tschwinge> Does building for x86 have any issues? + <tschwinge> matty3269: How is generally your understanding of the Hurd on + Mach system architecture, and on microkernel-based systems generally, and + on Mach in particular? + <matty3269> tschwinge: yes, it seems to be progressing... I've got mig + installed and it's just compiling now + <matty3269> hmm, not too great if I'm honest, I've done mostly monolithic + kernel development so having such low-level processes, such as + scheduling, done in user-space seems a little strinage + <tschwinge> Ah, yes, MIG will need a little bit of porting, too. I can + help with that, but that's not a priority -- first you have to get Mach + to boot at all; MIG will only be needed once you need to deal with RPCs, + so user-land/kernel interaction, basically. Before, you can hack around + it. + <matty3269> tschwinge: I have been running a GNU/Hurd system for a while + now though + <tschwinge> I'm happy to tell you that the schedules is still in the + kernel. ;-) + <tschwinge> OK, good, so you know about the basic ideas. + <braunr> matty3269: there has to be machine specific stuff in user space + <braunr> for initial thread contexts for example + <matty3269> tschwinge: Ok, just got gnumach built + <braunr> but there isn't much and you can easily base your work from the + x86 implementation + <tschwinge> Yes. Mach itself is the more difficult one. + <matty3269> braunr: Yeah, looking around at things, it doesn't seem that + there will be too much work involoved in the user-space stuff + <tschwinge> braunr: Do you know off-hand whether there are some old Mach + research papers describing architecture ports? + <tschwinge> I know there are some describing the memory system (obviously), + and I/O system -- which may help matty3269 to understand the general + design/structure. + <tschwinge> We might want to identify some documents, and make a list. + <braunr> all mach related documentation i have is available here: + ftp://ftp.sceen.net/mach/ + <braunr> (also through http://) + <tschwinge> matty3269: Oh, definitely I'd suggest the Mach 3 Kernel + Principles book. That gives a good description of the Mach architecture. + <matty3269> Great, that's my weekends reading then! + <braunr> you don't need all that for a port + <matty3269> Is it possible to run the gnumach binary standalone with qemu? + <braunr> you won't go far with it + <braunr> you really need at least one program + <braunr> but sure, for a port development, it can easily be done + <braunr> i'd suggest writing a basic static application for your tests once + you reach an advanced state + <braunr> the critical parts of a port are memory and interrupts + <braunr> and memory can be particularly difficult to implement correctly + <tschwinge> matty3269: I once used QEMU's + virtual-FAT-filesystem-from-a-directory-on-the-host, and configured GRUB + to boot from that one, so it was easy to quickly reboot for kernel + development. + <braunr> but the good news is that almost every bsd system still uses a + similar interface + <tschwinge> matty3269: And, you may want to become familiar with QEMU's + built-in gdbserver, and how to connect to and use that. + <braunr> so, for example, you could base your work from the netbsd/arm pmap + module + <tschwinge> matty3269: I think that's better than starting on real + hardware. + <braunr> tschwinge: you can use -kernel with a multiboot binary now + +[[hurd/running/qemu#multiboot]]. + + <braunr> tschwinge: and even creating iso images is so fast it's not any + slower + + <braunr> ah, the gnumach executable is a correct elf image + <matty3269> Is there particular reason that mach is linked at 0xc0100000? + <matty3269> or is that where it is expected to be in VM> + <tschwinge> That's my understanding. + <braunr> kernels commmonly sti at high addresses + <braunr> that's the "standard" 3G/1G split for user/kernel space + <matty3269> I think Linux sits at a similar VA for 32-bit + <braunr> no + <matty3269> Oh, I thought it did, I know it does on ARM, the kernel is + mapped to 0xc000000 + <braunr> i don't know arm, but are you sure about this number ? + <braunr> seems to lack a 0 + <matty3269> Ah, yes sorry + <matty3269> so 0xC0000000 + <braunr> 0xc0100000 is just 1 MiB above it + <braunr> the .text section of linux on x86 actually starts at c1000000 + (above 16 MiB, certainly to preserve as much dma-able memory since modern + machines now have a lot more) + <matty3269> so with gnumach, does the boot-up sequence use PIC until VM is + active and the kernel mapped to the linking address? + <braunr> no + <braunr> actually i'm not certain of the details + <braunr> but there is no PIC + <braunr> either special sections are linked at physical addresses + <braunr> or it relies on the fact that all executable code uses near jumps + <braunr> and uses offsets when accessing data + <braunr> (which is why the kernel text is at 3 GiB + 1 MiB, and not 3 GiB) + <matty3269> hmm, + <braunr> but you shouldn't worry about that i suppose, as the protocol + between the boot loader and an arm kernel will certainly not be the saem + <braunr> same* + <matty3269> indeed, ARM is tricky because memory maps are vastly differnt + on every platform + + +## IRC, freenode, #hurd, 2012-11-21 + + <matty3269> Well, I have a ARM gnumach kernel compiled. It just doesn't + run! :) + <braunr> matty3269: good luck :) + + +# IRC, freenode, #hurd, 2013-01-30 + + <slpz> Hi, i've read there's an ongoing effort to port GNU Mach to ARM. How + is it going? + <braunr> not sure where you read that + <braunr> but i'm pretty sure it's not started if it exists + <slpz> braunr: http://www.gnu.org/software/hurd/open_issues/arm_port.html + <braunr> i confirm what i said + <slpz> braunr: OK, thanks. I'm interested on it, and didn't want to + duplicate efforts. + <braunr> little addition: it may have started, but we don't know about it + + +# IRC, freenode, #hurd, 2013-09-18 + + <Hooligan0> as i understand ; on startup, vm_resident.c functions configure + the whole available memory ; but at this point the system does not split + space for kernel and space for future apps + <Hooligan0> when pages are tagged to be used by userspace ? + <braunr> Hooligan0: at page fault time + <braunr> the split is completely virtual, vm_resident deals with physical + memory only + <Hooligan0> braunr: do you think it's possible to change (at least) + pmap_steal_memory to mark somes pages as kernel-reserved ? + <braunr> why do you want to reserve memory ? + <braunr> and which memory ? + <Hooligan0> braunr: first because on my mmu i have two entry points ; so i + want to set kernel pages into a dedicated space that never change on + context switch (for best cache performance) + <Hooligan0> braunr: and second, because i want to use larger pages into + kernel (1MB) to reduce mmu work + <braunr> vm_resident isn't well suited for large pages :( + <braunr> i don't see the effect of context switch on kernel pages + <Hooligan0> at many times, context switch flush caches + <braunr> ah you want something like global pages on x86 ? + <Hooligan0> yes, something like + <braunr> how is it done on arm ? + <Hooligan0> virtual memory is split into two parts depending on msb bits + <Hooligan0> for example 3G/1G + <Hooligan0> MMU will use two pages tables depending on vaddr (hi-side or + low-side) + <braunr> hi is kernel, low is user ? + <Hooligan0> so, for the moment i've put mach at 0xC0000000 -> 0xFFFFFFFF ; + and want to use 0x00000000 -> 0xBFFFFFFF for userspace + <Hooligan0> yes + <braunr> ok, that's what is done for x86 too + <Hooligan0> 1MB pages for kernel ; and 4kB (or 64kB) pages for apps + <braunr> i suggest you give up the large page stuff + <braunr> well, you can use them for the direct physical mapping, but for + kernel objects, it's a waste + <braunr> or you can rewrite vm_resident to use something like a buddy + allocator but it's additional work + <Hooligan0> for the moment it's waste ; but with some littles changes this + allow only one level of allocation mapping ; -i think- it's better for + performances + <braunr> Hooligan0: it is, but not worth it + <Hooligan0> will you allow changes into vm_resident if i update i386 too ? + <braunr> Hooligan0: sure, as long as these are relevant and don't introduce + regressions + <Hooligan0> ok + <braunr> Hooligan0: i suggest you look at x15, since you may want to use it + as a template for your own changes + <braunr> as it was done for the slab allocator for example + <braunr> e.g. x15 already uses a buddy allocator for physical memory |