[lldb-dev] LLDB Evolution - Final Form
Zachary Turner via lldb-dev
lldb-dev at lists.llvm.org
Tue Sep 20 14:25:24 PDT 2016
I don't think anyone is ok with that. I just think that a better solution
is to document them. Why handle at runtime what is known about at compile
On Tue, Sep 20, 2016 at 2:24 PM Zachary Turner <zturner at google.com> wrote:
> Well, but StringRef for example is well documented. So it seems to me
> like there's an example of a perfectly used assert. It's documented that
> you can't use null, and if you do it asserts. Just like strlen.
> The issue I have with "you can't ever assert" is that it brings it into an
> absolute when it really shouldn't be. We already agreed (I think) that
> certain things that are well documented can assert. But when we talk in
> absolutes, it tends to sway people that they should always do that thing,
> even when it's not the most appropriate solution. And I think some of that
> shows in the LLDB codebase where you've got hugely complicated logic that
> is very hard to follow, reason about, or test, because no assumptions are
> ever made about any of the inputs. Even when they are internal inputs that
> are entirely controlled by us.
> On Tue, Sep 20, 2016 at 2:19 PM Greg Clayton <gclayton at apple.com> wrote:
> Again, strlen is a stupid example as it is well documented. All of llvm
> and clang are not.
> > On Sep 20, 2016, at 1:59 PM, Zachary Turner <zturner at google.com> wrote:
> > On Tue, Sep 20, 2016 at 1:55 PM Greg Clayton <gclayton at apple.com> wrote:
> > > On Sep 20, 2016, at 1:45 PM, Zachary Turner <zturner at google.com>
> > >
> > > I do agree that asserts are sometimes used improperly. But who's to
> say that the bug was the assert, and not the surrounding code? For
> example, consider this code:
> > >
> > > assert(p);
> > > int x = *p;
> > Should be written as:
> > assert(p);
> > if (!p)
> > do_something_correct();
> > else
> > int x = *p;
> > >
> > > Should this assert also not be here in library code? I mean it's
> obvious that the program is about to crash if p is invalid. Asserts should
> mean "you're about to invoke undefined behavior", and a crash is *better*
> than undefined behavior. It surfaces the problem so that you can't let it
> slip under the radar, and it also alerts you to the point that the UB is
> invoked, rather than later.
> > >
> > > What about this assert?
> > >
> > > assert(ptr);
> > > int x = strlen(ptr);
> > >
> > > Surely that assert is ok right? Do we need to check whether ptr is
> valid EVERY SINGLE TIME we invoke strlen, or any other function for that
> matter? The code would be a disastrous mess.
> > Again, check before you call if this is in a shared library! What is so
> hard about that? It is called software that doesn't crash.
> > assert(ptr)
> > int x = ptr ? strlen(ptr) : 0;
> > I find it hard to believe that you are arguing that you cannot EVER know
> ANYTHING about the state of your program. :-/
> > This is like arguing that you should run a full heap integrity check
> every time you perform a memory write, just to be sure you aren't about to
> > If you make a std::vector<>, do we need to verify that its internal
> pointer is not null before we write to it? Probably not, right? Why
> not? Because it has a specification of how it works, and it is documented
> that you can construct one, you can use it.
> > It's ok to document how functions work, and it is ok to assume that
> functions work the way they claim to work.
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