Re: [Valgrind-users] Do you already have a --tidoffset parameter?

[Sebastian <sc...@nb...>]

Hi,

On Fri, Mar 28, 2003 at 01:43:16PM -0500, Peter H Smith wrote:

> When I run a program under valgrind, pthread_self() will return a number
> between 1 and 50.  This doesn't catch some latent errors.  Consider this
> simplification of some bone-headed trace code:
 
> #define PENNY_WISE 5
> char header[PENNY_WISE];
> sprintf(header, "%d: ", pthread_self());
> fprintf(stderr, "%s%s\n", header, message);
 
> There is a latent buffer overrun here that won't be tripped under Valgrind
> because thread ids are always small.  I'd like to be able to set the base
> thread id to something like 0x800000000 or 0xFFFF0000 and test to be sure
> this buffer nonsense is not a problem.

While configurability might be a nice thing in general, this might be too
much. I have never seen code like the one you gave as example (and I have
audited quite a lot open source applications).

What might be nice in general would be to simulate a behaviour similar to
the native implementation. I.e. if libpthread gives high TID's, then
valgrind should, too. But as I have never dabbled with this features of
valgrind, this might be off the road, though.

Also, the program might also just misbehave on small TID's and behave
correctly at large TID's. Or produce a buffer overflow at small TID's. Or
negative ones. Etc. That quickly leads to "fuzzing" the application with
random data that might produce faults.


One can use other examples such as "malloc(0)", which I have seen in real
code to produce process-wide unique-id's. Valgrind or any other malloc
implementation might change this and return a constant (as zero bytes can
never be used), hence break the program. Or they do not. The point is, if
programs are broken without valgrind, valgrind should not try to produce
specific bordercases that might cause trouble.

(My point of view, but maybe the valgrind developers can support/nullify my
 points ;-)


> Peter H. Smith
> Advisory Software Engineer
> xSeries Systems Management
> IBM Server Group

ciao,
Sebastian

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