bug#43802: Knot: Linker runs very slowly and crashes during build

[Simon South]

Building Knot 3.0.0 using "guix build knot" consistently appears to hang
for me when it gets to this point during the linking stage:

    CCLD     knsec3hash
  ar: `u' modifier ignored since `D' is the default (see `U')
    CCLD     kdig
    CCLD     khost

While it sits here the compiler is tying up 100% of a single CPU
core. On my ROCK64 with 4 GB of RAM, it eventually crashes with an
internal error:

  gcc: internal compiler error: Killed (program cc1)
  Please submit a full bug report,
  with preprocessed source if appropriate.
  See <https://gcc.gnu.org/bugs/> for instructions.
  make[3]: *** [Makefile:5381: libzscanner/la-scanner.lo] Error 1
  make[3]: Leaving directory '/tmp/guix-build-knot-3.0.0.drv-0/knot-3.0.0/src'

dmesg shows the compiler was killed for running out of memory:

  cc1 invoked oom-killer: gfp_mask=0x100cca(GFP_HIGHUSER_MOVABLE), order=0, 
oom_score_adj=0
  CPU: 2 PID: 22340 Comm: cc1 Not tainted 5.8.11-gnu #1
  (...)
  
oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0,global_oom,task_memcg=/,task=cc1,pid=22340,uid=999
  Out of memory: Killed process 22340 (cc1) total-vm:2573780kB, 
anon-rss:2540708kB, file-rss:0kB, shmem-rss:0kB, UID:999 pgtables:5044kB 
oom_score_adj:0
  oom_reaper: reaped process 22340 (cc1), now anon-rss:0kB, file-rss:0kB, 
shmem-rss:0kB

On my x86_64 machine the build eventually completes (that machine has
much more memory), but there is the same, weirdly long delay during
linking while the compiler runs.

I see no such delay however when I build the code "manually", using
"guix environment --pure knot" or even "guix environment --no-grafts
--container knot" as the manual suggests. The build then completes
quickly and successfully on either machine; the problem appears to
happen only when guix-daemon is involved.

Is there a known issue that can cause the linker to consume orders of
magnitude more resources when run by the Guix build process?

Apart from rebuilding gcc with debugging symbols (which seems to make
Guix want to rebuild every other package in the system as well) and
trying to understand what the compiler is doing, how might I go about
diagnosing this?

-- 
Simon South
simon@simonsouth.net