4 ms·

It’s funny, this is the exact kind of thing I’d want on a non-x86 system. Raspberry Pico for example would be a great place for a 2KB HTTP server but with not s

It’s funny, this is the exact kind of thing I’d want on a non-x86 system. Raspberry Pico for example would be a great place for a 2KB HTTP server but with not support for HTTPS, IPv6, or for any non-x86 architectures it’s a bit of a non-starter for my use cases. Still, very cool project!

kragen 6y ago
The CPU architecture is actually the least of your concerns there—I'm pretty sure qemu-user can run httpdito on ARM with less than an order of magnitude performance overhead. There are a lot of embedded systems where an HTTP transaction per second per MHz would be more than sufficient. The bigger problem is that the Raspberry Pico is a dual-core Cortex-M0+, which doesn't have an MMU, so it can't run Linux and especially can't handle fork(). But httpdito is basically scripting the Linux system call interface in assembly language—it needs to run on top of a filesystem, an implementation of multitasking that provides allocation of different memory to different tasks, and a TCP/IP stack. Any one of these is probably a larger amount of complexity than the 296 CPU instructions in httpdito. The smallest TCP/IP stack I know of is Adam Dunkels's uIP. Running `sloccount .` in uip/uip cloned from https://github.com/adamdunkels/uip https://github.com/adamdunkels/uip gives a count of 2796 lines of source code ("generated using David A. Wheeler's 'SLOCCount'."). uIP can run successfully on systems with as little as 2KiB of RAM, as long as you have somewhere else to put the code, but for most uses lwIP is a better choice; it minimally needs 10KiB or so. uIP is part of Dunkels's Contiki, which includes a fairly full-featured web server and a somewhat less-full-featured browser. I think he got both the server and the browser to run in 16KiB of RAM on a Commodore PET, but not at the same time. (twIP http://dunkels.com/adam/twip.html http://dunkels.com/adam/twip.html is only 139 bytes of C source but doesn't support TCP or any physical-layer protocol such as Ethernet, PPP,or SLIP.) However, Adam Dunkels has also written Miniweb http://dunkels.com/adam/miniweb/ http://dunkels.com/adam/miniweb/, which implements HTTP and enough of TCP and IP to support it, in 400 lines of C. It needs at least 30 bytes of RAM. Like twIP, it doesn't provide a physical layer. But that's solvable.
- jimmyed 6y ago
  Not having MMU means there's no virtual memory and instructions refer to physical memory addresses, cmiiw? You say Linux won't work without MMU, it can't handle physical addresses? Moreover, why won't fork() work without MMU?
  - aduitsis 6y ago
    I would hazard a guess that fork is nowadays implemented by the clone(2) system call, which does use copy-on-write depending on its arguments. It's possible that there are deep assumptions in the Linux code that some fundamental software or hardware memory handling capabilities are present.
  - pjc50 6y ago
    Without an MMU, you can't do paging. That means fork() cannot do the normal copy-on-write business, because there's no page table to copy the entries in. You also have no inter-process security, so everything can crash everything else including the kernel, and no swap. It used to be the case that all Linux executables had to be loaded at the same virtual address, but ASLR may have removed requirements of this kind. https://stackoverflow.com/questions/38549972/why-elf-executables-have-a-fixed-load-address https://stackoverflow.com/questions/38549972/why-elf-executa...
    - kragen 6y ago
      I'm pretty sure Linux ELF has always allowed you to specify the initial load address. When I first wrote StoneKnifeForth https://github.com/kragen/stoneknifeforth https://github.com/kragen/stoneknifeforth its load address was 0x1000, but at some point Linux stopped allowing load addresses lower than 0x10000 by default (vm.mmap_min_addr). I originally wrote it in 02008, using the lower load address, and fixed it in 02017. It's still not using 0x804800 like normal executables but 0x20000. ASLR does not affect this. Maybe you mean that before ELF support, Linux a.out executables had to be loaded at a fixed virtual address? That's possible—I started using Linux daily in 01995, at which point a.out was already only supported for backward compatibility.
  - 6y ago

kragen 6y ago

The CPU architecture is actually the least of your concerns there—I'm pretty sure qemu-user can run httpdito on ARM with less than an order of magnitude performance overhead. There are a lot of embedded systems where an HTTP transaction per second per MHz would be more than sufficient. The bigger problem is that the Raspberry Pico is a dual-core Cortex-M0+, which doesn't have an MMU, so it can't run Linux and especially can't handle fork(). But httpdito is basically scripting the Linux system call interface in assembly language—it needs to run on top of a filesystem, an implementation of multitasking that provides allocation of different memory to different tasks, and a TCP/IP stack. Any one of these is probably a larger amount of complexity than the 296 CPU instructions in httpdito. The smallest TCP/IP stack I know of is Adam Dunkels's uIP. Running `sloccount .` in uip/uip cloned from https://github.com/adamdunkels/uip https://github.com/adamdunkels/uip gives a count of 2796 lines of source code ("generated using David A. Wheeler's 'SLOCCount'."). uIP can run successfully on systems with as little as 2KiB of RAM, as long as you have somewhere else to put the code, but for most uses lwIP is a better choice; it minimally needs 10KiB or so. uIP is part of Dunkels's Contiki, which includes a fairly full-featured web server and a somewhat less-full-featured browser. I think he got both the server and the browser to run in 16KiB of RAM on a Commodore PET, but not at the same time. (twIP http://dunkels.com/adam/twip.html http://dunkels.com/adam/twip.html is only 139 bytes of C source but doesn't support TCP or any physical-layer protocol such as Ethernet, PPP,or SLIP.) However, Adam Dunkels has also written Miniweb http://dunkels.com/adam/miniweb/ http://dunkels.com/adam/miniweb/, which implements HTTP and enough of TCP and IP to support it, in 400 lines of C. It needs at least 30 bytes of RAM. Like twIP, it doesn't provide a physical layer. But that's solvable.

jimmyed 6y ago
Not having MMU means there's no virtual memory and instructions refer to physical memory addresses, cmiiw? You say Linux won't work without MMU, it can't handle physical addresses? Moreover, why won't fork() work without MMU?
- aduitsis 6y ago
  I would hazard a guess that fork is nowadays implemented by the clone(2) system call, which does use copy-on-write depending on its arguments. It's possible that there are deep assumptions in the Linux code that some fundamental software or hardware memory handling capabilities are present.
- pjc50 6y ago
  Without an MMU, you can't do paging. That means fork() cannot do the normal copy-on-write business, because there's no page table to copy the entries in. You also have no inter-process security, so everything can crash everything else including the kernel, and no swap. It used to be the case that all Linux executables had to be loaded at the same virtual address, but ASLR may have removed requirements of this kind. https://stackoverflow.com/questions/38549972/why-elf-executables-have-a-fixed-load-address https://stackoverflow.com/questions/38549972/why-elf-executa...
  - kragen 6y ago
    I'm pretty sure Linux ELF has always allowed you to specify the initial load address. When I first wrote StoneKnifeForth https://github.com/kragen/stoneknifeforth https://github.com/kragen/stoneknifeforth its load address was 0x1000, but at some point Linux stopped allowing load addresses lower than 0x10000 by default (vm.mmap_min_addr). I originally wrote it in 02008, using the lower load address, and fixed it in 02017. It's still not using 0x804800 like normal executables but 0x20000. ASLR does not affect this. Maybe you mean that before ELF support, Linux a.out executables had to be loaded at a fixed virtual address? That's possible—I started using Linux daily in 01995, at which point a.out was already only supported for backward compatibility.
- 6y ago