Utility Code

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Bitfield functions

BitUnion classes


FastAlloc has been removed from the code base since late May 2012. Instead the build scripts will pick up tcmalloc (a malloc() version used also at Google), the observed performance gain of replacing tcmalloc over fastalloc is around 6%.


panic, fatal, warn, inform, hack: which?

There are error and warning functions defined in src/base/misc.hh: panic(), fatal(), warn(), inform(), and hack(). The first two functional have nearly the same effect (printing an error message and terminating the simulation), and the latter three print a message and continue. Each function has a distinct purpose and use case. The distinction is documented in the comments in the header file, but is repeated here for convenience because people often get confused and use the wrong one.

  • panic() should be called when something happens that should never ever happen regardless of what the user does (i.e., an actual m5 bug). panic() calls abort() which can dump core or enter the debugger.
  • fatal() should be called when the simulation cannot continue due to some condition that is the user's fault (bad configuration, invalid arguments, etc.) and not a simulator bug. fatal() calls exit(1), i.e., a "normal" exit with an error code.
  • warn() should be called when some functionality isn't necessarily implemented correctly, but it might work well enough. The idea behind a warn() is to inform the user that if they see some strange behavior shortly after a warn() the description might be a good place to go looking for an error.
  • hack() should be called when some functionality isn't implemented nearly as well as it could or should be but for expediency or history sake hasn't been fixed.
  • inform() Provides status messages and normal operating messages to the console for the user to see, without any connotations of incorrect behavior. For example it's used when secondary CPUs being executing code on ALPHA.

The reasoning behind these definitions is that there's no need to panic if it's just a silly user error; we only panic if m5 itself is broken. On the other hand, it's not hard for users to make errors that are fatal, that is, errors that are serious enough that the m5 process cannot continue.

random number generation

reference counting pointers