On Mon, Feb 1, 2021 at 1:52 PM Robert M. Münch
<robert.mue...@saphirion.com> wrote:
>
> I know all about the problems of FP comparison, and yes I know that I need to
> provide more information. What makes me suspicious is, that I have a bunch of
> equivalent tests before the failing one, and all pass. I still believe in the
> determinism of programs. Hence, this is all really strange.
>
> I run the C test code (without any Go) in GDB and the values are correctly
> set. This is how the data looks before the call, setting the correct values:
>
> 804 YGNodeCalculateLayout(root, YGUndefined, YGUndefined,
> YGDirectionLTR);
> (gdb) p root.layout_.dimensions
> $9 = {
> _M_elems = {nan(0x400000), nan(0x400000)}
> }
>
> and this is after the call:
>
> (gdb) p root.layout_.dimensions
> $13 = {
> _M_elems = {320, 10}
> }
>
> I write a C wrapper function, that outputs the return value just before it's
> returned and makes its way through the Go FFI. Here is the output before the
> call:
>
> YGNodeLayoutGetWidth: 1.#QNAN0 7FC00000
> YGNodeLayoutGetHeight: 1.#QNAN0 7FC00000
>
> and after the call
>
> YGNodeLayoutGetWidth: 320.000000 43A00000
> YGNodeLayoutGetHeight: 1000000020040877300000.000000 6258D727
>
> So, why are the values before the call are different in C and the C side
> within the Go program? I mean why once 0x400000 and 0x7FC00000? I would have
> expected that the C code behaves the same.
> And as you can see the 320 is set in both cases, but the expected 10 is a
> totally screwed up floating-point value.
>
> Could this be an alignment problem? Does CGO add some wrapping code, which
> does some strange things?
>
> Unfortunately, I didn't find a way, how I can enter the C code from a
> debugger when using the Go binary. Looks like there is no C debug information
> available.
cgo adds multiple wrapping functions.
I don't know what the problem is here. I can imagine several
different possibilities. Show us the code, and we won't have to
guess. Thanks.
Ian
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