Re: Preview: portable dumper

[Jacob Bachmeyer]

> (Or we could just randomize per-user and dump Emacs the first time it
> runs for a particular user?  If we do that after loading ~/.emacs, we
> also improve people's startup time.  Invalidating and regenerating the
> dump when configuration changes would be a challenge though.)

That should not be too difficult, if you can track which files were read 
when creating the dump and store some fields from the stat(2) 
information on those files in the dump.  I am using this approach in a 
packaging system that I am developing to close a race between attaching 
a file to an archive handle and actually writing the archive, at which 
time the digest of the file is computed.  (I wanted to avoid reading 
input files twice.)

I take a conservative approach and verify that the 
st_{ino,dev,size,blocks,{m,c}tim{e,.tv_nsec}} fields are all unchanged.  
For my use, writing the archive produces a hard failure if this check 
fails; for Emacs, failing that check would indicate "time to rebuild the 
fast-load cache".


On the other hand, I think that per-user dumps are a bad idea--the Emacs 
dump is an inscrutable binary blob and therefore a good place for an 
intruder to hide persistent nastiness.  This could allow an intruder to 
add a back door to a user's Emacs in a difficult-to-detect manner while 
needing only temporary access to that user's account, say, from 
exploiting any program that user runs.


-- Jacob