Re: [Valgrind-users] How to mark separate bits as undefined?

[John R. <jr...@bi...>]

> Hello, I was wondering if it is possible to partially mark
> a memory location as undefined when running under valgrind.

Quoting the documentation  http://valgrind.org/info/tools.html :
>  Memcheck tracks addressability at the byte-level, and initialisation of values at the bit-level. As a result, it can detect the use of single uninitialised bits, and does not report spurious errors on bitfield operations

Therefore: Run memcheck under a debugger, and watch while memcheck checks this program:
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#include <stdlib.h>
int *p;
int main()
{
	p = (int *)malloc(100);
	p[5] &= 0xec6da539;  /* clear some bits, leave the rest uninit */
	return p[0xff & p[5]];  /* indexing by uninit is an immediate error */
}
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