[PATCH] Division by zero

[Anders Rönnholm]

Ping.

> -----Original Message-----
> From: Anders Rönnholm
> Sent: den 5 juni 2014 14:17
> To: Jordan Rose
> Cc: cfe-commits at cs.uiuc.edu; Daniel Marjamäki
> Subject: Re: [PATCH] Division by zero
> 
> Hi Jordan,
> 
> New patch and some comments.
> 
> +inline void inline_func3(int x) {
> +  var = 77 / x;
> +}
> +void ok_inline(int x) {
> +  var = 77 / x;
> +  inline_func3(x);
> +  if (x==0){}
> +}
> 
> This is an example where we should still be warning. Why aren't we?
> 
> It doesn't warn here because blockid is in the value and not the key as it
> should. I have made a set of symbol-block-frame as you suggested and that
> fixes this problem.
> 
> 
> +// RUN: %clang_cc1 -analyze -analyzer-checker=core.DivideZero2 -analyzer-
> output=text -verify %s
> 
> We should never be running path-sensitive checks without the rest of the
> core checkers.
> 
> There is a small problem here. It looks like the DivideZero checker makes the
> assumtion that because it can't see that a variable is zero then it's not zero so
> all variables in our tests have the range reg_$0<x> : { [-2147483648, -1], [1,
> 2147483647] }. I have removed the range check in my checker to make it
> work otherwise i would have to change the DivideZero checker.
> 
> 
> +  const ZeroState *ZS = C.getState()->get<DivZeroMap>(SR);
> +  return (ZS && *ZS == ZeroState(C.getBlockID(), C.getStackFrame()));
> 
> ...now I'm wondering about the wisdom of using a map for this. What if the
> same symbol is constrained in two stack frames? Would it make more sense
> to keep around a set of symbol-block-frame triples, rather than a map from
> symbols to block/frame pairs?
> 
> Or can this not happen because a value can only be used once along a certain
> path before it is constrained to be non-zero?
> 
> Changed to a set of symbol-block-frame triples to make the above example
> work.
> 
> 
> +def DivZeroChecker2 : Checker<"DivideZero2">,
> +  HelpText<"Check for division by variable that is later compared against 0.
> Either the comparison is useless or there is division by zero.">,
> +  DescFile<"DivZeroChecker2.cpp">;
> +
> 
> I'm not sure this is really a core checker, since it's safe to run the analyzer
> without it. But we don't have a category for "useful C checks that should be
> on by default" yet. Anton was looking at reorganizing the categories, but the
> problem is that everything outside of "alpha" is something people expect to
> be able to rely on when using scan-build.
> 
> Any ideas for this particular checker, or for the general issue?
> 
> I ok with having it as an alpha, or something else. I just put it in core since the
> other DivideZero checker is there.
> 
> //Anders
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