4 ms·

I'm wondering if you can build an actual "Linux from scratch" with this as the lowest level, without the need to use a host system at all.

vitiral 3y ago
Without structs? Good luck...
- gigel82 3y ago
  LFS already has several "stepping stones" where it walks through a whole set of C compilers from very old ones compiling slightly newer / more capable ones and so on. Perhaps with a few more "layers of compilers" on top you can get a very early GCC going.
  - FpUser 3y ago
    >"Perhaps with a few more "layers of compilers" on top you can get a very early GCC going." Applause. Best comment ;)
- DesiLurker 3y ago
  wonder how many extra bytes for structs?
  - vitiral 3y ago
    In my experience, probably at least a 200-400 lines of C (another 512 bytes minimum? I don't know the conversion). The problem is not just declaring structs but accessing them, referencing them, accessing/referencing fields and subfields, etc. That has to all be in the syntax. For such a minimal project you can ignore initialization. I did all this while adding maybe 500 lines of C to GitHub.com/vitiral/fngi. Never tried for this level of minimalism though.
    - geocar 3y ago
      Once upon a time, when += was spelled =+, struct members in C were global names whose "values" were the offsets from the beginning of the struct[1]; a.b is simply a[ptrtab[b]] and a->b is a[0][ptrtab[b]]. [1]: This is why all of the names of struct members in unix are "needlessly" prefixed; i.e. struct stat.st_mode is not struct stat.mode because that could conflict with struct foo.mode until the early 1980s.
      - DesiLurker 3y ago
        Ah that explains it, I wondered about those old struct defs.
mjevans 3y ago
I can't help but wonder if this is written in x86-16 bit mode to implicitly use Real Mode BIOS functions and platform interfaces as well. There's something to be said for taking advantage of that existing code; but if that's a dependency it should be part of the environment manifest. Everything has (most things have) a context where it might be useful and that should be included in the explanation so a tool isn't misused and so incorrect expectations aren't set.
- xorvoid 3y ago
  It’s written in x86-16 real mode because all immediates are smaller and switching to 32-bit mode takes a fair amount of code. I would have preferred 32-bit mode because real mode is awkward with its seg:off addressing scheme. Using the bios functions just allows it to have “not-boring” examples easily.
  - mjevans 3y ago
    That's true, but it's still a sort of library dependency. Even for very tiny computers with a lot of hardware assistance, the basic ROM for communicating with the world in a useful way is bigger.
fosslinux 3y ago
Not using this, but tangentially related is (full disclosure, i am a maintainer of this project) live-bootstrap, which uses about a KB of binary to do a full "Linux from scratch" style thing - read https://github.com/fosslinux/live-bootstrap/blob/master/parts.rst https://github.com/fosslinux/live-bootstrap/blob/master/part... for all 143 steps you have to go through to get there.
- gigel82 3y ago
  Wow, just reading through the list of steps was fascinating!

vitiral 3y ago

Without structs? Good luck...

gigel82 3y ago
LFS already has several "stepping stones" where it walks through a whole set of C compilers from very old ones compiling slightly newer / more capable ones and so on. Perhaps with a few more "layers of compilers" on top you can get a very early GCC going.
- FpUser 3y ago
  >"Perhaps with a few more "layers of compilers" on top you can get a very early GCC going." Applause. Best comment ;)
DesiLurker 3y ago
wonder how many extra bytes for structs?
- vitiral 3y ago
  In my experience, probably at least a 200-400 lines of C (another 512 bytes minimum? I don't know the conversion). The problem is not just declaring structs but accessing them, referencing them, accessing/referencing fields and subfields, etc. That has to all be in the syntax. For such a minimal project you can ignore initialization. I did all this while adding maybe 500 lines of C to GitHub.com/vitiral/fngi. Never tried for this level of minimalism though.
  - geocar 3y ago
    Once upon a time, when += was spelled =+, struct members in C were global names whose "values" were the offsets from the beginning of the struct[1]; a.b is simply a[ptrtab[b]] and a->b is a[0][ptrtab[b]]. [1]: This is why all of the names of struct members in unix are "needlessly" prefixed; i.e. struct stat.st_mode is not struct stat.mode because that could conflict with struct foo.mode until the early 1980s.
    - DesiLurker 3y ago
      Ah that explains it, I wondered about those old struct defs.

mjevans 3y ago

I can't help but wonder if this is written in x86-16 bit mode to implicitly use Real Mode BIOS functions and platform interfaces as well. There's something to be said for taking advantage of that existing code; but if that's a dependency it should be part of the environment manifest. Everything has (most things have) a context where it might be useful and that should be included in the explanation so a tool isn't misused and so incorrect expectations aren't set.

xorvoid 3y ago
It’s written in x86-16 real mode because all immediates are smaller and switching to 32-bit mode takes a fair amount of code. I would have preferred 32-bit mode because real mode is awkward with its seg:off addressing scheme. Using the bios functions just allows it to have “not-boring” examples easily.
- mjevans 3y ago
  That's true, but it's still a sort of library dependency. Even for very tiny computers with a lot of hardware assistance, the basic ROM for communicating with the world in a useful way is bigger.

fosslinux 3y ago

Not using this, but tangentially related is (full disclosure, i am a maintainer of this project) live-bootstrap, which uses about a KB of binary to do a full "Linux from scratch" style thing - read https://github.com/fosslinux/live-bootstrap/blob/master/parts.rst https://github.com/fosslinux/live-bootstrap/blob/master/part... for all 143 steps you have to go through to get there.

gigel82 3y ago
Wow, just reading through the list of steps was fascinating!