klange changed the topic of #osdev to: Operating System Development || Don't ask to ask---just ask! || For 3+ LoC, use a pastebin (for example https://gist.github.com/) || Stats + Old logs: http://osdev-logs.qzx.com New Logs: https://libera.irclog.whitequark.org/osdev || Visit https://wiki.osdev.org and https://forum.osdev.org || Books: https://wiki.osdev.org/Books
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<nortti> apropos the vax discussion last evening, why does it use that kind of paging anyways? is the 512 byte page size to align with the sector sizes on disk media?
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<netbsduser> nortti: yes, exactly that
<netbsduser> they were pioneering with respect to virtual memory and were concerned that a page size not equal to the physical block size of disks would be harmful to that
<nortti> and I guess linear page tables were for simplicity of implementation?
<netbsduser> i think it would´ve been specifically for the simplicity of implementing pageable user page tables
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<zid> hello feet
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<heat> gello
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<mcrod> hi
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<Ermine> heat: how do you feel yourself
<heat> i feel like ass
<heat> at least i feel better than yesterday morning but that's a low point innit
<heat> still have issues eating but im kinda hungry
<heat> dreamed about eating kitkats ngl best dream ever
<Ermine> that sucks
<heat> it does but At Least Im Not Puking
<heat> And Im Watching The Footy
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<gog> HI I'M SAD
* kof123 .oO( innit init system )
<gog> and i'm doing capslock by accident
<kof123> why are you sad gog?
<Cindy> gog: hi sad i'm sad
* ChavGPT hugs gog
<ChavGPT> there there
<heat> gog: SAD is actually a type of company here in portugal
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<Ermine> gog: may I pet you
<gog> hi
<gog> yes
<gog> probably nothing idk
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<x8dcc> is it a good idea to store the FPU/SSE state with fxsave when initializing multitasking and then using that as base when creating new tasks?
<heat> erm
<heat> maybe?
<heat> so, it's kinda useless
<heat> there's only 1/2 words of state you need to set when initializing an FPU context, and those can be set directly in the xsave map easily
<bslsk05> ​github.com: Onyx/kernel/arch/x86_64/fpu.cpp at master · heatd/Onyx · GitHub
<heat> if everything else in the FPU area is zeroed you have an EZPZ FPU SQZ
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<x8dcc> that's helpful, I will do that instead
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<x8dcc> thank you :)
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<heat> np
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<geist> yah i think they explicitly set it up so that all zeros is the default. at some point i decoded how all of that compressed xsave stuff works, but its a little wonky
<geist> but i think some of the wonkiness is because of the zero-is-default-state mechanic
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<geist> nortti, netbsduser: also re: the vax linear paging, it was an era when a full 32bit address space was huuuuuge, generally well beyond the size of the largest machine
<geist> so the ability to restrict the user space with a length field and not use up a large page table probably seemed like a good idea
<geist> though i guess the radix tree style page table also accomplishes fairly the same thing
<geist> as far as i know even in the later vaxen, when the initial 29 bit physical address space was startig to be a problem they still used the linear map
<geist> seems like the kernel aspace would start getting pretty cramped with page tables by then
<nortti> how big is a page table entry on VAX?
<geist> 4 bytes, fairly standard set of fields by modern standards
<geist> but in initial designs 29 bits was the max physical size, the real virtual space is chopped up in a few weird ways, though not weird if you've worked with avr32, mips, or sh-4. fairly standard hard chopping of the whole aspace into user, identity map, kernel, etc
<geist> only thing in the page table entries thats kinda neat is it has the ring level in it, so it's more powerful than 386's mapping of rings to user/supervisor. you can set which ring the page becomes accessible in
<samis> that's why VMS has a number of rings and unlike x86 actually uses them
<samis> right?
<geist> yeah. i think the other way of looking at it is vax had a number of rings that it intrinsically used (or VMS did at least), and intel copied that with 286 but was never really used that much
<nortti> hm, OS/2 used rings for device drivers on 80286, right? what did it do for 386?
<geist> i think OS/2 was the main user of rings, yeah
<geist> i booted OS/2 on qemu one time and broke into it a few times to see what the state of the cpu was and it was definitely using ring 2 a lot
<geist> how that really gets you much protection since the paging scheme only gives you 2 i dunno
<geist> but i suspect they split the kernel up into core kernel and then some sort of supervisor level drivers/etc code so maybe there was a bit of advantage there
<geist> you can learn quite a bit by booting something like dos with emm386.sys or win 3.1 on qemu and just breaking into it and see how it's using the GDT and page tables
<geist> pretty educational
<zid> or forgeddaboutit
<zid> it's 2023 baby, 64bit virtual address spaces for everyone
<nortti> does any CPU architecture actually give 64 bits of virtual address space?
<zid> Not sure actually
<nortti> afaict 39, 48, and 56 seem like the common values
<zid> "48 is the best I can do" --CPU makers
<geist> fairly sure ia64 does
<nortti> oh, interesting
<nortti> does it just do a deeper radix tree?
<geist> iirc it chops the full virtual space into 8 separate zones, each zone has it's own paging structure
<geist> so you can use that however you want, 2:2, 7:1, 1:6:1, etc
<geist> so each paging structure deals with 2^61 of it
<geist> but basically that means you have up to 8 things to context switch
<geist> depending on how you choose to use it
<geist> and no ia64 does not use a radix tree at all, it's a very very different design
<geist> closer to POWER/PPC but it has two modes that you can choose per structure iirc
<geist> basically part of the control register set up
<geist> long vs short page table entries, etc. but one of the modes looks a bit like vax in the sense that it's a large linear page table that lives in virtual space
<geist> iirc that's the short page table entry mode, the long mode is i think closer to POWER in that it's a huge hash table
<geist> i think those page table entries are 16 bytes long, iirc
<geist> been a while, actually heat grokked it all at once
<heat> nortti: don't forget 36 btw, afaik 36 is also pretty common
<heat> hm sorry 36 bits seemsto be common for a physical address
<heat> also it's 57
<heat> you go 48 -> 57 cuz of 9 extra bits
<heat> and on ARM, 49 -> 58
<heat> IF they have 58-bit addressing, which I don't think they do?
<childlikempress> I thought arm had a 52-bit thing?
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<heat> (ARM has an extra bit because it has two radix trees instead of one)
<heat> idk, probably
<heat> i don't remember all the details, i just did 48-bit
<heat> *49
<netbsduser> interestingly the VMS port to Alpha was done by implementing a vax macro assembly 2 alpha compiler
<heat> good
<heat> what a great solution
<heat> up yours dave cutler
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<childlikempress> remember #define rax x0 from apple or whatever it was
<heat> with all the registers arm has you could even define-emulate MMX
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<heat> imagine the possibilities
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<childlikempress> ooh I just realised something
<childlikempress> the x87 stack has 8 elements
<childlikempress> so you can shove the entire thing into an avx512 register and emulate the stack ops with shuffles
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<heat> thank you childlikempress, very cool!
<x8dcc> heat: I am setting [edx + fpu_data.mxcsr] (allocated+0x18) to dword 0b0001111110000000 (0x1F80) but now I am getting a x87 floating point exception :(
<heat> then something else is wrong
<heat> because That Just Works(tm)
<x8dcc> rest of the 512 bytes are zeros
<x8dcc> the exception occurs on a fstp instruction
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<kof123> one small step for x87, one giant leap towards pages in registers
<heat> wait
<heat> why the fuck do you have x87 instructions?
<x8dcc> not sure
<childlikempress> kof123: the avx512 state is 2kb
<childlikempress> and an avx512 instruction has a 2-bit register size header whose meanings are: 16 bytes, 32 bytes, 64 bytes, unassigned
<childlikempress> SO they could double the register size still, and literally store a page in registers
<childlikempress> HTH.HAND
<heat> oh, 32-bit codegen uses x87 by default
<heat> ew
<childlikempress> -msse or sth
<childlikempress> or just do 64 bit
<heat> x8dcc: did you configure the FPU properly
<heat> where are you catching this exception? hopefully not the kernel?
<x8dcc> I think I configured fpu properly, but I usually my errors happen because I think I did something right when I didn't
<x8dcc> childlikempress: I use -msse and -msse2 currently
<heat> where
<heat> what is crashing?
<x8dcc> my %f format for printf
<x8dcc> and I only have kernel, I don't have userspace or anything
<heat> oh god
<heat> don't
<x8dcc> I haven't touched the project in some months
<heat> rm -rf %f handling
<heat> and then rm -rf -msse -msse2 from your kernel's CFLAGS
<childlikempress> don't do fp in kernel
<x8dcc> well I don't have anything else haha
<zid> afaik in linux to do fp you have to call a special lock + init function, do your shit, then release?
<zid> and it's only used by like, the crypto api
<x8dcc> childlikempress: why is it bad to use fp in kernel?
<childlikempress> I think there's a flag you can pass to tell the compiler to refuse to emit any kind of fp code? Or do a softfp even when the hardware supports hardfp? (Which amounts to the same thing--don't link in the softfp lib, so you'll get a link error if you try to use it)
<zid> -mgeneral-regs-only for life
<zid> Then never bother to make a libgcc, so that if you ever need one it fails to link
<childlikempress> yeah that was it
<childlikempress> no why what's wrong with libgcc
<zid> it'll have the float cast etc code in it
<childlikempress> oh
<heat> x8dcc: floating point sucks, and you'll need to consistently save/restore FPU regs after kernel entries and exits
<heat> which is expensive
<x8dcc> well that's a bit depressing
<heat> why?
<x8dcc> because I spent a lot of time trying to fix stuff related to this for nothing
<x8dcc> but whatever
<zid> fairly sure you were told not to last time too
<x8dcc> don't remember, but you might be right
<x8dcc> learned in the process so I don't mind that much
<childlikempress> I mean tbf it _should_ work, since you're not actually doing any context switching (I presume)
<bslsk05> ​godbolt.org: Compiler Explorer
<childlikempress> so it is a bit suspicious
<zid> you still need to enable floating point in the control reg and stuff
<childlikempress> that it doesn't. But still, shouldn't, so
<zid> and make sure it generates the right alignments etc
<heat> i can't convince 32-bit gcc to FPU using SSE
<heat> zid: and actually load the mxcsr/fxsave state
<zid> is that not what I said
<heat> no you just mentioned the control regs
<childlikempress> heat: -mfpmath=sse
<bslsk05> ​github.com: Onyx/kernel/arch/x86_64/fpu.cpp at master · heatd/Onyx · GitHub
<zid> Loads the source operand into the MXCSR control/status register.
<zid> control register.
<heat> ok
<x8dcc> well what should I work on next
<zid> 802.11b
<childlikempress> can you allocate memory
<heat> childlikempress: ew fpmath=sse generates horrendous code
<x8dcc> yes I can
<childlikempress> i suggest being able to allocate memory
<heat> for the float func at least
<x8dcc> I spent a lot of time
<childlikempress> heat: it has to return on x87 because of the abi
<zid> I spent hardly any time on mine it's awful <3
<childlikempress> try void f(float *x) { *x += 10; }
<x8dcc> I mean a lot of time adding alignment for allocations for fxsave
<x8dcc> for nothing (for now)
<zid> you'll want a userspace libc though?
<x8dcc> I don't have an userspace, I have most of my libk code in libc but I just stopped even syncing it with libk because I was not using it
<zid> you'll -> you will
<zid> future tense
<zid> You just wrote it early is all
<x8dcc> yeah I know
<x8dcc> still, I think it's missing whatever it is that separates libk from libc :)
<heat> have you considered getting to userspace?
<zid> my userspace is amazing isn't it heat
<heat> yes
<heat> high quality
<heat> emulators
<zid> 0 syscalls
<zid> recompile entire kernel to change the userspace program
<x8dcc> heat: sure, but I don't really know where to start
<zid> I just shipped a binary with my kernel, mapped it cpl3 at 2M
<zid> and iret'd the kernel to it
<heat> x8dcc: what do you have?
<zid> can build from there
<x8dcc> I saw that, zid
<zid> timer to bring you back to kernel, filesystem to let you pick an /init, etc
<zid> good excuse to add APs afterwards also
<gog> hi
<gog> i don't program kernal
<zid> web development gives a wage
<zid> so that's understandable
<x8dcc> heat: not sure what to tell you, you can kinda guess by the filenames in the kernel dir, I guess
<heat> what kernel dir?
<x8dcc> hard to say what I have because I am not sure what I need/am missing
<x8dcc> heat: meant src/kernel/*.c
<heat> i don't know what your OS is
<heat> sorry
<bslsk05> ​github.com: fs-os/src/kernel at main · fs-os/fs-os · GitHub
<zid> I have also not seen a single line of it
<x8dcc> I sent the link some months ago, I am sure of that
<zid> that'll be why
<zid> you also have a non-name name
<zid> for both irc and github
<zid> so it's hard to remember you/it between the month breaks
<x8dcc> the most important commit was made by heat
<x8dcc> zid: I understand, I don't mind
<heat> why do you have so many fucking commits holy shit
<x8dcc> I change stuff, I guess
<zid> rebase -i it down to about 3
<heat> they're wayyyyyyyy too granular pal
<x8dcc> I am sorry
<zid> meh they seem fine
<zid> It's just they would normally be hidden behind merges, or be part of a series
<zid> I don't like the lack of title style
<x8dcc> what?
<zid> "Align task stack to 16 bytes" -> "task/stack.c: Align stack to 16 bytes"
<bslsk05> ​github.com: fs-os/src/kernel/multitask.asm at main · fs-os/fs-os · GitHub
<zid> and then that'd normally be part of a small series of fixes that got 'merged'
<x8dcc> zid: I see
<zid> so you'd end up with [01/05] task: fix a, [02/5] task: fix b
<zid> etc
<zid> and you get a nice sort of visual grouping going on
<x8dcc> I get anxious when I have too many uncommited changes
<zid> so commit them?
<zid> You don't have to push before you rebase
<heat> your kernel should have way less asm
<zid> my locak tree is usually [master] then [wwwwww] [wasdf] [asdeir]
<zid> :D
<x8dcc> heat: Why does it matter
<zid> with commits on each branch that are 'fopd' 'asdasd'
<heat> unreadable, unportable, hard to extend
<x8dcc> zid: I honestly have to admire that
<zid> x8dcc: why not write it all in asm?
<zid> take whatever you're about to say as your answer
<zid> and apply it to the bits of asm in your code
<zid> done
<x8dcc> I like asm, but the entire thing would take too much time
<zid> that is infact, a fuck load of files ending in .asm
<zid> is that.. more than the .c?
<x8dcc> don't think so
<heat> your heap doesn't actually expand
<x8dcc> my heap is trash
<x8dcc> everything is trash
<heat> you also have no way of allocating physical pages
<heat> i'm giving you ideas pal
<heat> if they're trash, make em good
<zid> heat when are you adding an allocator to my kernel
<heat> when are you giving me a back rub?
<zid> I figured you'd want to give ME a back rub
<x8dcc> I don't even know why I would need to expand my heap or to allocate physical pages
<heat> why would i give peter crouch a back rub
<x8dcc> it's a bit frustrating
<zid> cus getting to touch footballers is your life goal?
<heat> if crouchy gave me a back rub he'd still be touching me
<heat> hence i win
<heat> x8dcc: dynamic memory allocation
<heat> for... dynamism?
<zid> getting touched and someone else allowing you to touch them are deeply different
<heat> like, you can roll with the old-ass UNIX struct inode inos[NINODES]; and then allocate from that, and panic if you run out
<heat> but that's old-ass and bad
<x8dcc> idk, this whole FP thing demotivated me for real
<heat> why
<x8dcc> well it was something I wanted to fix for months and turns out it was for nothing
<x8dcc> I know it's my fault but still sad
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<heat> going on wild goosechases is like osdev 101
<heat> it happens
<kazinsal> yep
<kazinsal> that's like, 90% of the hobby
<zid> It's literally some people's jobs to contribute to linux, they spend 2 years writing some big patchset
<zid> and it gets rejected
<x8dcc> I guess I would be sad there as well
<x8dcc> but yeah, I get it happens
<x8dcc> so anyway, what do you think I should work on next for userspace?
<zid> I already said it
<heat> page allocation
<heat> then a proper heap
<heat> like copy the slab allocator paper or something
<zid> heat refuses to give me a shitty proper heat :(
<heat> then get a proper scheduler
<zid> heap*
<zid> heap: write me a shitty heat
<heat> heatp
<heat> brkbrkbrkbrkbrkbrkbrk
<x8dcc> what is exactly page allocation for?
<heat> paging
<heat> but in page aligned page-sized chunks
<heat> it's like dynamic allocation but in pages
<samis> sbrksbrksbrksbrksbrk
<heat> like, sbrk asks for memory, you map some pages
<zid> I have that bit
<heat> or the slab allocator needs more slabs, you ask for pages from the alloc
<zid> I want a PROPER HEAP
<heat> then one may think "oh hrm this page thing is a really adequate and useful unit for memory allocation sometimes"
<x8dcc> heat: hmm okay, I see. I guess I can look more into that
<x8dcc> thank you
<heat> so you get allocators asking for pages, caches caching files in page units (page cache??)
<heat> np
<heat> the page is the basis of everything in a kernel
<heat> ever noticed how PATH_MAX is 4096, the common size of a page?
<x8dcc> I hadn't noticed, to be honest
<heat> normal people dont notice PATH_MAX yeah
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<heat> everyone asks what is PATH_MAX but no one asks how is PATH_MAX :(
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<gog> how is PATH_MAX
<zid> fine thanks how is /etc/shadow
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<gog> mysterious
<zid> Shadow is my edgelord name.
<zid> Etc Shadow.
<gog> i don't want to be an edgelord anymore
<gog> i want to be a normal person with normal thoughts
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<zid> But what happens if the seal in your left eye fails and nobody knows you have it!?
<gog> what
<bslsk05> ​tvtropes.org: Chuunibyou - TV Tropes
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<gog> oh
<gog> that is me though
<zid> I should watch more of that chuuni girl series
<zid> she calls dr pepper a mana potion that's all I remember of the first ep that I watched
<gog> i'm not a very good or smart person tbh
<gog> and i need to fluff myself up to seem better
<zid> have you considered that
<zid> most people are way shitter than you think you are
<zid> and you're actually like 80th percentile
<zid> wtb more crappy light novels
<zid> oh, something new came out 30 mins ago, Love under the Blue Moon - Falling in love again.. ehhh..
<zid> guess I am reading this!
<gog> i should go to bed now
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