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Re: Reading uninitialized memory


From: Andrew Vaught
Subject: Re: Reading uninitialized memory
Date: Sat, 26 Jan 2002 14:48:14 -0700 (MST)

On 26 Jan 2002, Torbjorn Granlund wrote:

> Andrew Vaught <address@hidden> writes:
> 
>     In order for checker and similar products (purify, Electric Fence) to
>   prevent the propagation of undefined values, dataflow analysis at
>   compile-time is required.  The unused value from memory is read into a
>   register and then is sometimes not used.  Because checker is doing its
>   thing at run-time, it is too late for the dataflow analysis.
> 
> Well, just as it can trace pointers, it could trace values coming from
> unitialized memory.

   You have to then decide what you mean by 'use'.  Checker defines 'use'
as 'loading from memory'.  When you saw the read from uninitialized heap,
you'd have to set a flag, which would then have to be checked whenever the
variable was 'used', whatever that is taken to mean.

      Andy

-----------------                        XOLD(K,IC,I)=
Andy Vaught               ....        DO ITERS=1, 10  XOLD(K,IC,I)
address@hidden     |  |   /CALLMSOLVE(A,B,X,I,ITERS,TOL)+(RANNYU(0)
Arizona State University  ======|WRITE(6,'(I5,2X,F12.6)')ITERS,TOL -HALF)
Tempe, Arizona USA        OOOOOO \ENDDORETURN PARAMETER(ZERO=1.D0)*TENTH*DELTA




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