I just tried 4.03.0 (no flambda), recompiling all, and the problem still
occurs. (And thanks to opam and a fast compiler, this process was quick and
easy!)

Jesper, those numbers coming through in that problem do look similar.
Anyone know what they are? They strike me as familiar, but I can't place
it: looks like escaped octal triplets, with occasional letter and
terminated by some low-valued marker (\1,\2) -- and it's a proper string,
not like random memory.

Gabriel, I am perfectly happy with getting bitten by "clever code", due to
a smarter compiler -- well, provided there's a way to express what's
wanted. :)

Jeremy, I will try to reduce this to a simpler case with just tgls/opengl,
and see if I can trap the flawed cases, or make it easily reproducible.
Right now I have to head out to work though.

Thanks for the input, guys!


On Sun, May 8, 2016 at 10:52 PM, Jeremy Yallop <yallop@gmail.com> wrote:

> On 8 May 2016 at 18:08, Anthony Tavener <anthony.tavener@gmail.com> wrote:
> > TL;DR: Constant string like "fontColor" can (rarely) come out like
> > "\220\552\663\1" after foreign call to OpenGL.
> >
> > I was seeing glitches in render output, and have tracked it down to
> "uniform
> > variable names" which are given as constant strings, but on OpenGL side
> they
> > can appear malformed.
> >
> > OCaml call:
> >
> >     let color = Gl.get_uniform_location sp "fontColor" in
> >
> > In a trace of the OpenGL calls from the running program the result is
> > usually like this:
> >
> >     glGetUniformLocation(program = 3, name = "fontColor") = 3
> >
> > But on occasion (once in several hundred calls) has garbage:
> >
> >     glGetUniformLocation(program = 3, name = "\220\552\663\1") = -1
> >
> > The really odd thing to me is the structure of these strings (some more,
> not
> > all from "fontColor"):
> >     "\220    \774\1"
> >     "\220\332\663\1"
> >     "\440\\\665\1"
> >     "\220\552\663\1"
> >     "\220J\663\1"
> >     "\660\117\553\2"
> >     "\440\220w\2"
> >
> > For reference, Gl.get_uniform_location is implemented thusly (in tgls):
> >
> >   let get_uniform_location =
> >     foreign ~stub "glGetUniformLocation"
> >       (int_as_uint @-> string @-> returning int)
> >
> >
> > I am using OCaml 4.03+flambda. The problem occurs with -O3 or no
> > optimizations. The problem might have happened with prior versions (I
> > haven't been able to work with OCaml much in the past year), and my own
> code
> > is of course suspect. :)
> >
> > I'm posting in case this rings a bell for someone, that they might know
> > what's going on. I'm continuing to debug.
>
> If you have a reproducible test-case I'd be interested to take a look at
> this.
>