I think I found it.
commit be8d0c60fcd3bb8615740d55ba300460c9062679 (HEAD -> master) Author: Stephen R. van den Berg srb@cuci.nl Date: Mon Jul 6 00:13:44 2020 +0200
Stdio.Buffer: Put null in a freed io->output.u.object.
src/modules/_Stdio/buffer.cmod | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
This should/might fix it. Which is not to say, that: - The valgrind diagnostics might point at other issues. - The fact that gcc-10 and Pike are incompatible is disconcerting. It likely is a compiler bug, but it is worrisome nonetheless.