Today I started experiencing mysterious hanging of edje_cc
during build. "The French are at it again" I thought, and
after spending a while bisecting, I found the culprit.
It's 7f53d91583.
So, what is happening in here?
The idea here was fundamentally sound; compute a special
hash value for event descriptors, taking range between 0
and 63 (on 64-bit systems) and 0 and 31 (on 32-bit systems),
then use a mask sized 32-bit or 64-bit (depending on your
system) and check early if to bail out from callback_call,
saving some resources. So far so good.
The problem is in the way the mask is handled. We're applying
the hash as the shift value like, `x |= (1 << hash)`. On 32-bit
systems this is okay, but on 64-bit systems, C's dumb silent
coercion rules kick in, since the left side of the expression
is 1, a literal with type signed int; that means our shifting
range is limited to 31 and what we get is... undefined behavior.
This is obviously not what we want, so take a 1ULL value as a
base. The previous thing seemingly worked on x86_64 (nobody
reported any issues) and interestingly it worked for me too
for a while (on ppc64le), but undefined behavior can be
unpredictable, so...
This shouldn't need a commit message as long as this, but I'm
making it proportional to the amount of time I wasted on this.
9ca573f40f