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
<vdamewood> night: 00:00 AM o'Clock at mornight.
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<vdamewood> mrvn: ^
<heat> is it just me or do arm64 page table permissions map horribly with any actual use case
<heat> s/with/to/
<heat> you have 2 execute-nevers for some reason (how is this remotely useful), there's a read-only bit instead of a write bit, a not-global bit
<heat> it's like everything is stupidly backwards
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<mrvn> heat: that's not the global bit, it's the process-memory bit
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<mrvn> and execute-never is the data bit :)
<heat> arm64 page table bits are the stupidly-backwards bit :P
<heat> like seriously, a read-only bit?
<mrvn> I bet it saved 1 NOT gate each time
<heat> well this is arm64, not arm
<heat> I would hope they're not trying to be cost-effective
<mrvn> arm has the same not-X bits. changing it for 64bit mode would be horrible.
<mrvn> saving a gate is probably less about cost than propagation times
<mrvn> or just about writing the vrml easier
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<geist> they just have two XN bits for user and kernel
<geist> why though is a good case, would you ever want the kernel to be able to execute but not user? etc
<geist> heat: which one is the read only bit you're tlaking about?
<geist> i think the perm bits being the way they are is something to do with the modify bit mechanism
<geist> which is a bit backwards, but makes sense
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<heat> geist, AP[2:1]
<heat> per D4.4.4 "Data access permission controls"
<heat> AP[2] Selects between read-only and read/write access.
<heat> AP[1] Selects between Application level (EL0) control and the higher Exception level control.
<heat> I don't know why you implemented those macros the way you did
<heat> confusingly, when AP[2] is set, it's read-only instead of read-write
<heat> geist, ok maybe a possible use for PXN is to try and stop kernel exploitation that leads to execution of user code
<heat> that kinda makes sense I guess?
<heat> if you mark everything user-space PXN
<gamozo> That's literally the point of PXN
<gamozo> it's a mitigation
<gamozo> it means you can't jump to a user-provided code (you have to ROP/find an exploit path to load dynamic code into the kernel)
<heat> why wouldn't you just not support it
<gamozo> It's honestly one of the better mitigations (arguably, PAN matters way more). Back in the day we'd just get PC control in the kernel and point it to a (known) user address. Defeating ASLR in the same pass, it was great
<gamozo> I miss those days
<heat> just like you need special arm64 instructions (or touch a system register) to touch user-space memory
<heat> does UXN on a kernel page make sense?
<heat> or is the "access" on AP[1] just a data access and not an instruction fetch
<gamozo> Might as well, reduces amount of ROP gadgets, and cleans up the address space a bit, but in this era we just switch page tables on syscalls anyways so *shrug*
<gamozo> that being said, I'm not too familiar with ARM, I mainly know the x86 equivs of SMEP/SMAP
<heat> wait didn't I discuss this with geist the other day
<heat> im having a weird mix of a flashback and the early stages of a good old mandela effect
<heat> lets see
<gamozo> I thought every day we just rsetart the same convos on here
<heat> ok yeah haha I did
<heat> yeah right
<heat> how about that itanium haha
<heat> pretty cool
<gamozo> unikernels amirite?
<gamozo> "my USB driver is done"
<heat> so just found out the windows iso doesn't support EL TORITO
<heat> wtf microsoft
<gamozo> more like, el doritos
<gamozo> cause it's super dusty and old
<heat> given it's a summer day, and the local hometown ice cream chain is UDF (United Dairy Farmers), I want to go for a shake now
<klys> for something to talk about, looking for a UI: I want pages of gridded cels containing each: pile of pictures, picture, empty cel. this is for storyboarding.
<heat> we're already discussing arm64 mmu details and breaking the time continuum
<klys> oh sry
<heat> not a problem
<heat> this a kernel weirdos version of a time loop movie
<klys> time loops should break traditional assumptions on where people come from and luck. ergo you get movie drama with this plot device
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<vdamewood> heat: Do you even need El Torito with UEFI?
<klange> Absolutely.
<klange> EFI can not read ISO9660.
<klange> (In so far as it is not in the list of required filesystems to support.)
<heat> yeah you need it
<klange> So you need some way to throw an EFI-compatible FAT filesystem on the disk.
<klange> I've been doing this thing for years where the FAT blob is where all my files go, and I build it specially to have sector alignment with the enclosing ISO 9660, and then the ISO 9660 "files" reference the data in the FAT.
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<geist> yah PAN on arm64 works even better: you just set the bit and now EL1 can't access EL0 period *except* via a set of dedicated load/store instructions
<geist> so basically you implement user copy in terms of those laod/stores and then you dont have to toggle the bit or whatnot like you do on x86
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<zid> I have an amazing meme but it's slightly too political to post :'(
<psykose> post it u wont
<bslsk05> ​twitter: <janusrose> Supreme Court rules 6-3 that the mysterious organization known as SEELE can continue the Human Instrumentality Project and trigger the Third Impact as described in the Dead Sea Scrolls
<psykose> LMAO
<zid> My only regret is that the crossection of people who know about us politics and eva enough to get this is not infinite
<moon-child> what's eva
<ptrc> evangelion anime
<bauen1> i think i still understand too little of the backstory of eva to understand it lol
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<zid> eva's not that hard to understand if told, but figuring out THAT is what it's saying from watching it is very hard
<zid> like Primer
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<geist> haha
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<mrvn> Why do people always ask: How to do X without the-one-feature-required-to-do X?
<clever> mrvn: maybe they got half way to the solution, and think that is the only way there
<clever> and are trying to help the helpers, to know where to start from
<heat> mrvn, context?
<bslsk05> ​drewdevault.com: Porting Doom to Helios
<heat> ddevault, congrats!
<ddevault> thanks!
<heat> i've never even tried it
<heat> at this point i'll just wait for my opengl support first lol
<ddevault> it's easy if your OS already has the important pieces, especially if it's a Unix-like OS
<ddevault> doom does not use OpenGL
<heat> it can though
<klange> Hm, if I let the demo play it GPFs just a few seconds in.
<ddevault> yeah, when the demo picks up the shotgun
<ddevault> known issue, don't really care to fix it
<ddevault> just start the game before that happens ;)
<heat> WONTFIX
<ddevault> or debug it and send a patch, it's just a null dereference which can probably be fixed fairly easily
<heat> why does a null deref get a gpf
<ddevault> make gdb/make gdbc will respectively start the VM with gdb remote and connect to it in a shell
<j`ey> I dunno how to start the game, always goes to demo for me
<ddevault> press enter until you enter gameplay
<ddevault> but if your PC is fast enough it will probably hit the shotgun and crash before you have a chance to, see timing issues mentioned in the post
<j`ey> doesnt work *shrug*
<klange> I know upstream doomgeneric still has the finetangent buffer overrun; that segfaulted in my aarch64 builds 'cause the table was ending up at the end of a segment
<ddevault> oh, and you need the doom branch of helios
<ddevault> which expands the initial cspace size and configures the framebuffer appropriately
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<heat> you'd never have a buffer overrun if it was written in R U S T
<bslsk05> ​stackoverflow.com: c++ - How to build a header only lib without inline statment for each function? - Stack Overflow
<clever> heat: only if you dont use the unsafe flag
<heat> I, as the CTO of Rust, have never used unsafe before
<clever> heat: how shal you interface with asm?
<heat> you rewrite the asm in rust, as you should
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<clever> heat: and rust can deal with interrupt handlers and _start?
<j`ey> yes
<heat> *caveman noises*
<ddevault> "can rust __________?" yes
<ddevault> can rust solve world hunger? yes
<ddevault> can rust end poverty? yes
<ddevault> can rust get you a girlfriend? actually no on that one
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<mrvn> world hunger (still) is a myth. There is enough food for everyone. There just isn't anyone willing to pay for it.
<mrvn> ddevault: boyfriend?
<heat> can rust create a crippling division between the rich and poor? also yes
<ddevault> it's just being hoarded by the rich*
<ddevault> yeah, rust can get you a boyfriend for sure
<ddevault> cargo install boyfriend or whatever
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<zid> heat: wrong tense
<bauen1> ddevault: actually you're wrong, there is a girlfriend crate, but not a boyfriend one: https://crates.io/search?q=boyfriend vs. https://crates.io/search?q=girlfriend
<ddevault> rip
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<mrvn> When they designed clang why did they make the frontend compile all codes for a stack machine just so the middle end can then compile that into SSA eliminating all the memory accesses first thing?
<heat> because they designed llvm and not clang
<heat> clang was just something they built on top of it
<mrvn> doesn't change the question.
<heat> not using llvm would've been horrible for clang and llvm
<j`ey> makes it simpler to write frontends
<mrvn> j`ey: that's the point I would disagree with
<heat> in fact AFAIK llvm was a virtual machine before it ever was a backend
<j`ey> mrvn: well that is why
<heat> stack based vms aren't crazy :)
<mrvn> a IL with unlimited registers would have been easier
<j`ey> llvm has unlimited registers
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<mrvn> j`ey: only once it's turned into SSA
<j`ey> it always has unlimited registers
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<mrvn> How does llvm deal with spilled registers and setjmp/longjmp? Does it always spill registers the same way on every function call?
<mrvn> or does it switch ways when it sees a setjmp?
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<zid> heat you're a rust professional
<zid> does it have designated initializers
<zid> or does this guy have to write out 256 zeros for his array that I implemented via {[3] = "hello", [7] = "meow"} etc
<zid> for this LUT
<mrvn> does rust allow uninitialized variables at all?
<heat> i think that at the end of the day the US prison system needs a good and thoughful reform so that ex-inmates can live a normal life after their sentence, reducing inequality and stopping them from becoming repeat offenders
<heat> i help that answers your question
<heat> hope*
<j`ey> zid: it doesnt have that C way like that, no
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<heat> please feel free to reach out to me if you have any more rust answers I can question
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<j`ey> you can make an array with all 0s, then fill in with foo[3] = 'hello' etc
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<heat> j`ey, hello local linux kernel business rep
<heat> what does KBUILD_BUILD_VERSION do
<heat> it's included in uname -v and it's bothering me
<j`ey> thats all it does
<heat> "#1 SMP PREEMPT_DYNAMIC Sat, 25 Jun 2022 20:22:01 +0000" WHAT IS HASHTAG ONE
<heat> is it just something you manually increment for some reason?
<j`ey> the amount of times you built the kernel
<j`ey> $ cat .version
<j`ey> 1814
<heat> hmmmmmmmmmmm
<heat> ok
<heat> interesting
<j`ey> PREEMPT_DYNAMIC, fancy
<heat> j`ey, what do you work on btw?
<heat> PREEMPT_DYNAMIC is fancy, yes
<heat> part of the Arch Linux experience
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<j`ey> currently Realm stuff
<bslsk05> ​developer.arm.com: Documentation – Arm Developer
<heat> so like sgx?
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<heat> but hopefully less broken
<j`ey> I dont know about SGX, but secure VMs stuff
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<j`ey> so not just secure regions used by the main OS
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<geist> yeah the realm stuff i haven't fully grokked to see how it's precisely different from the existing trust zone stuff
<geist> it clearly is, but i'm not entirely sure the mechanism end to end to pull it off
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<bslsk05> ​queue.acm.org: Linear Address Spaces - ACM Queue
<zid> This reads like one of those rants by a guy who thinks his teeth are talking to him
<mrvn> GeDaMo: what's your point?
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<GeDaMo> No point, I thought it might be of interest
<mrvn> I'm not sue what his point is actually.
<mrvn> sure
<mrvn> Does he wan't just a software controlled TLB cache? or does he want type and range checked pointers?
<mrvn> He glorifies having tagged addressess but then vilifies CHERI which tags pointers.#
<mrvn> but it gives him great hope.
<zid> "TLB misses are annoying so I won't support arrays"
<zid> not exactly an amazing take
<mrvn> "The very first thing any realtime nucleus or operating system kernel does is implement an abstract object store on top of the linear space." What is that supposed to be? I just have a virtual Address space that gets used up linearly till it runs out (and then it should loop around).
<gorgonical> mrvn: I took that to mean the slab allocator?
<gorgonical> I think that's what he means
<gorgonical> I also think his take on CHERI is really strange -- I see it as a really interesting way to "revive" segmentation with a modern take
<mrvn> From what I understand it implements the C/C++ model of a pointer into memory. It has a start and and end and you can subdivide the memory. Each subdivision may only access memory within it's own start/end.
<mrvn> After some dvisions you create objects via a return from new or an allocator.
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<bslsk05> ​IRCCloud pastebin | Raw link: https://irccloud.com/pastebin/raw/whcVnPWH
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<heat> we are indeed the professional systems programmers
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<mrvn> and we don't like getting spam
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<heat> the discord people are amateur systems programmers
<heat> we are the professionals
<heat> i appreciate that they understand that
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