Re: [Valgrind-users] best methodology to debug a Linux daemon written in C++

[tom f. <tf...@al...>]

 writes:
> Hi All,
>
> I have a bunch of C++ application which runs as daemons in Linux.
>
> Another reason for it to crash might be corrupted input data that it
> processes.
>
> I used --leak-check=yes and --log-file=foo.txt options with Valgrind.
>
> However, Valgrind did not report any invalid write/read or
> uninitialized variable errors which may have caused the crash.

It might be that your daemon is a `true' daemon, in that it does the
double fork trick.  In that case, you want to make sure you use the
command line option "--trace-children=yes".

Less like is that you might be hitting the issue that Valgrind cannot
detect all possible errors.  See:

  http://www.valgrind.org/docs/manual/mc-manual.html#mc-manual.machine

I believe there is a semi-recent paper from a group out of UMass
Amherst which also goes into detail about the types of errors dynamic
analysis tools can find, and valgrind is one of the tools they
evaluate.

> FAQ on Valgrind's official website says that this is the nature of
> Valgrind that you can not change such that it can not replicate the
> native execution environment.

I do not think this is an issue with the change in execution
environment.  That's normally more of an issue with e.g. timed sections
of code or threading.

> What is the best debugger options to use with Valgrind to debug a
> Linux daemon ?

Other than the potential lack of --trace-children, your options seem
fine.

> Should I attach Valgrind to already running process ? or Is it ok to
> start the daemon with Valgrind in shell script ?

It is not possible to attach valgrind to a process after execution has
started, due to the nature of how it works.  It'll be obvious when
you read the above link: what would the `V' bits get set to when you
attach, for example?

-tom