> I do not understand. The below error is an uninitialised value error.
> Why do you say you cannot catch the errors ?
Valgrind points to them, but I don't seem to confirm the uninitialization.
> You just have to use monitor get_vbits at the time of the error
> to investigate more in depth where the error comes from,
> and if needed, relaunch the execution after having added some
> breakpoints earlier in the program flow, and again use get_vbits
> to try to understand where the uninit error comes from.
Easier said than done :)
I've tried but there are a lot of local variables:
int retval;
struct rs *rs = (struct rs *)p;
int deg_lambda, el, deg_omega;
int i, j, r,k;
data_t u,q,tmp,num1,num2,den,discr_r;
data_t lambda[NROOTS+1], s[NROOTS]; /* Err+Eras Locator poly
* and syndrome poly */
data_t b[NROOTS+1], t[NROOTS+1], omega[NROOTS+1];
data_t root[NROOTS], reg[NROOTS+1], loc[NROOTS];
int syn_error, count;
and lines where they can be used before initialization: ~ 300.
> Yes, the monitor get_vbits only knows about address+length.
> So, you need to do something like
> (gdb) p &myvar
> (gdb) p sizeof(myvar)
> and then use
> (gdb) monitor get_vbits <address> <size>
> to get the vbits.
Yes, but in some cases the sizeof indicates the size of the pointer (not
the size of the allocated memory). So I had to browse the code to get
the size of the allocations/structs involved.
> When valgrind reports that the origin of an uninit var is in a function,
> then it means it is one of the local variables of the function.
> Not the arguments of this function.
OK, that's why it is difficult to find this. Specially because it is a
3rd party library. Since the line valgrind pinpoints is not
accurate/relevant, we are in doubt about where the error comes from.
(I'm not saying its valgrind's fault, of course, it already is an
extremely useful tool, as is).
> If you want to detect buffer over or under run in stack and global
> variables, then yes, the experimental exp-sgcheck tool is your friend.
OK, so it is not applicable to this case of uninitialized stack variables.
What is strange is that I never faced such a shortcoming in my own code.
In my code valgrind always points to the location of the error exactly.
Does this happen because this is a library that I link with? Or because
of the nature of the error?
Thanks.
--
João M. S. Silva
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