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Re: [RESEND PATCH 03/12] golang/xenlight: fix string conversion in generated toC functions

On Fri, Jun 18, 2021 at 11:00:26AM +0000, George Dunlap wrote:
> > On May 24, 2021, at 9:36 PM, Nick Rosbrook <rosbrookn@xxxxxxxxx> wrote:
> > 
> > In gengotypes.py, the toC functions only set C string fields when
> > the Go strings are non-empty. However, to prevent segfaults in some
> > cases, these fields should always at least be set to nil so that the C
> > memory is zeroed out.
> > 
> > Update gengotypes.py so that the generated code always sets these fields
> > to nil first, and then proceeds to check if the Go string is non-empty.
> > And, commit the new generated code.
> > 
> > Signed-off-by: Nick Rosbrook <rosbrookn@xxxxxxxxxxxx>
> So wait — if you do
> var foo C.typename
> Then golang won’t automatically zero out `foo`?
> That seems like a bug really; but assuming this fixes real behavior you’ve 
> encountered:

I would have to dig in again to figure out exactly what Go/cgo is doing
here, and whether or not this is a bug. But, the behavior I observed was
that without these nil assignments, I would sometimes get segfaults in
libxl_string_copy. This patch ensures that libxl__str_dup is not called
in the empty string case, thus avoiding the segfault.
> Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxx>




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