Timothy Sample <samplet@ngyro.com> writes:

> The problem goes away if I move “useSubstitutes” above “reservedSize”,
> which has type “off_t”.  I’m guessing this is because of something fishy
> with “_FILE_OFFSET_BITS”, but I’m not sure what just yet.

Here’s my best guess as to what is going on.  In “nix-daemon.cc” the
order of includes causes “off_t” to be defined before
“_FILE_OFFSET_BITS”, which results in it being something like a 32-bit
signed integer.  In “local-store.cc”, “_FILE_OFFSET_BITS” gets set
first, yielding a 64-bit “off_t”.  This causes all of the addresses in
the “Settings” struct to be mismatched after “reservedSize”.  I plugged
in “sizeof(off_t)” into the “printMsg” calls from before, and (lo and
behold) I saw 4 from “nix-daemon.cc” and 8 from “local-store.cc”.

The following patch fixes the problem: