Hello,
I plan to build an experimental tool and I am considering to build my
work on Valgrind. Hence I would like to ask you for comments, if my idea
is feasible. I plan to build a dynamic verifier of C/C++ programs with a
non-deterministic behaviour (e.g. MPI programs). Generally I want to
explore all possible runs of a program in a single run.
I would like to achieve something like this.
int main()
{
int x = nondeterministic_choice(0, 1); // set to x 0 or 1
if (x > 0) {
printf("%i\n", x);
}
return 0;
}
When the program arrives to nondeterministic_choice, its state is
remembered and the program continues with the first choice (x=0). When
it terminates, the program returns to the saved position and the
execution continues with x=1. (I am now interested only in single
threaded programs that do not communicate with the system.)
I do not want to simply use system "fork", because I am expecting a
large number of branching and I want to understand a memory layout to
have possibility to merge executions.
As far I understand Valgrind implementation, I can implement my idea as
Valgrind tool like this:
- nondeterministic_choice is the client request. It stores the current
state of thread (everything in struct ThreadState) and then it continues
with the first choice of nondeterministic_choice.
- The memory in the the following run can be monitored in a similar way
as in memcheck. It allows to implemented a copy-on-write mechanism and
backup changed memory.
- When the program terminates, the thread state and changed memory will
be restored to the point when it was saved and the another path is
executed.
I would like to ask you for any comments but I have also the following
questions:
- It is sufficient to backup struct ThreadState (and its members) +
memory state to fully catch program state in a restorable form?
- It is possible to set a callback (in Valgrind tool) for an event
directly after program termination (return in main/exit call), but still
have Valgrind in a fully functional form, where I can restore my saved
thread and normally continue in computation.
Thank you,
Stanislav Bohm
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