On Wed, 2007-10-03 at 01:15 +0000, Adam Leventhal wrote:
> > thank you for the explanation. What would cause these symbols to change?
> > The
> > only thing that I changed between build was the introduce parallelism
> > between
> > uts and lib build plus additional parallelism in uts build.
>
> dtrace -G chooses a randomly generated prefix for the symbols. They should
> change every time a workspace is built.
But my inner two-year-old compels me to ask:
Why?
if they were actually random, the values in the examples were just large
enough that collisions would occur frequently enough to bother people
but be annoyingly hard to reproduce.
So I cheated. (I read the libdtrace code; it looks like this is in
usr/src/libdtrace/common/dt_link.c).
Assuming I found the right place, it's not actually random.
It uses ftok(path, 0) on the file; that ftok invocation produces a
24-bit integer based on 12 bits of device and 12 bits of inode number.
This is actually better than a truly random value that small as it makes
collisions less likely, at least on small filesystems.
I (and, well, anyone who has to use wsdiff) have this thing about build
reproduceability -- it's best if the same source tree produces the same
objects. Can we do something more collision-resistant but deterministic
so as to not cause these sorts of false positives for wsdiff?
- Bill
_______________________________________________
dtrace-discuss mailing list
[email protected]
