WIP: Add wrt1900acs ARMv7 target

[phodina]

This is still WIP attempt to add support for ARMv7 WRT1900ACS router

• [ ] Currently the build fails on building busybox as a dependency for haveged. I found a patch that should fix the issue regarding the time structure being 64-bit on 32-bit platform. However I don't know how to apply the patch. @telent @mathiashro could you please help me with applying it in nixwrt/overlay.nix?

    CC      libbb/sysconf.o
    CC      libbb/time.o
  libbb/time.c: In function 'get_mono':
  libbb/time.c:260:14: error: '__NR_clock_gettime' undeclared (first use in this function); did you mean 'clock_gettime'?
    260 |  if (syscall(__NR_clock_gettime, CLOCK_MONOTONIC, ts))
        |              ^~~~~~~~~~~~~~~~~~
        |              clock_gettime
  libbb/time.c:260:14: note: each undeclared identifier is reported only once for each function it appears in
  make[1]: *** [scripts/Makefile.build:197: libbb/time.o] Error 1
  make: *** [Makefile:743: libbb] Error 2
building '/nix/store/bm2yya8vy9ql5f62kahk3vibw47jsjsn-haveged-1.9.2-armv7l-unknown-linux-musleabi.drv'...

[telent]

This is exciting, first non-MIPS target. Will take a look shortly

[phodina]

Yes I've spare WRT1900ACS router which is armv7l based and I've compiled custom OpenWRT build for it. Also there is serial line attached to reflash if it gets bricked.

However, I think it would be better to prepare an issue where we can discuss how to support cross-compilation for multiple architectures and define steps to get there.

[phodina]

@telent Do you think you could spare time for review?

[telent]

  I found a patch that should fix the issue regarding the time structure being 64-bit on 32-bit platform. 

Seems to be a pair of patches inside another patch, which I think is slightly beyond the ability of fetchpatch to understand. You'd have to download it and extract them locally, and then it'd be a simple matter of

  busybox = stripped (super.busybox.overrideAttrs (o: {
    postConfigure = "true";

    patches = o.patches ++ [ "0001-date-Use-64-prefix-syscall-if-we-have-to.patch" "0001-time-Use-64-prefix-syscall-if-we-have-to.patch" ];
  }));

or something like that. I am curious, though - this is almost the same busybox derivation as used in upstream NixOS, does it not work on Arm 32bit there either? I understand that armv7 is not a first-class target for NixOS but it might be worth trying to patch upstream

[telent]

How much work do you think it would be to make an image that runs on qemu arm? I don't have any suitable ARM hardware, but it would give me confidence when looking at ARM changes that I hadn't broken everything

[cyplo]

A sidenote - I have some ARM routers that could lend/donate if that would be helpful ? No worries if not as well tho :)