Re: [Valgrind-users] Hopefully a n00b question

[Nicholas N. <nj...@cs...>]

On Mon, 20 Feb 2006, Brendan Drew wrote:

> First, Valgrind (I'm running 3.1.0 on a dual dual core opteron box in pure 
> 32bit mode) really doesn't seem to like static (scalar) variables. When I run 
> code which uses static variables, memcheck complains about invalid reads of 
> size 4 (not surprising since the variables in question were uint32_t's). The 
> error messages went away when I got rid of the static variables, which is 
> consistent with what I've seen elsewhere. Is this related to issues with 
> static arrays? I don't know the C++ ABI well enough, but I'd expect that 
> static scalars are allocated in the data section (together with global static 
> arrays), as opposed to the stack which is used for local variables, so I'm 
> pretty certain that these issues aren't related.

You need to give us more specific information.  Do you have a small test 
case that exhibits the behaviour?  What does Valgrind's output look like?

> Second question is a bit more troublesome: I get different behavior when 
> executing a program under Valgrind (specifically, memcheck) than I do when 
> just executing from the command line. In this case, I get a SIGSEGV which 
> refers to a null pointer being dereferenced. That's fine --- I get why the 
> null pointer deref should cause a segfault, the problem is that this doesn't 
> happen when not running under Valgrind. The program continues executing 
> normally, which is not the behavior one would expect when deref'ing a null 
> pointer. Any thoughts?

Sometimes bugs can crash a program when running under Valgrind that don't 
crash it normally, and vice versa.  They're still bugs that should be fixed, 
though.

Nick