arm64, valgrind floating point instruction produces different result

[Bernhard Übelacker <bernhardu@mailbox.org>]

Hello list,
I was trying to do some debugging in bug [1071656].

But for some reason I receive with arm64
in a process running with valgrind
and one without valgrind different results
from the following floating point instruction:

  => 0xaaaaaaaa4948 <ConvertToRational+104>:     fcvtas  w5, d8


With plain GDB:
  (gdb) print $w5
  $2 = 323


With valgrind+GDB:
  (gdb) print $w5
  $2 = 322


And therefore the CI run fails and led to this bug [1071656] (at least with arm64).
I was trying this first in a qemu arm64 VM on amd64,
but could observe this on real arm64 hardware too.

Is there some knowledge about such an issue, or how to avoid this?


Kind regards,
Bernhard

[1071656] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1071656