Re: Unreachable code diagnostic

[Josh Triplett <josh@joshtriplett.org>]

On Fri, Feb 24, 2017 at 10:07:59AM -0800, Matthew Wilcox wrote:
> I was recently sent some code that looked like this:
> 
> int foo()
> {
> 	lock();
> 	return bar();
> 	unlock();
> }
> 
> When you're restructuring code that contains locks, this is a
> *really* easy mistake to make.  I've done it myself.  But there's no
> compiler warning for it!  gcc doesn't have it, sparse doesn't have it.

Sparse does have a warning (via -Wcontext) for this, if you annotate
lock() and unlock() with __acquires(somelock) and __releases(somelock),
which expand to __attribute__((context(somelock,0,1))) and
__attribute__((context(somelock,0,1))) respectively.  You'll get a
warning that foo() returns with the lock held.

Not at all perfect, but it does have reasonable handling of
conditionals, including a way to handle cond_lock().