Re: GTY: Explicitly reject 'string_length' option for (fields in) global variables (was: [PATCH] pch: Fix streaming of strings with embedded null bytes)

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Jul 5, 2023 at 9:51 AM Thomas Schwinge <thomas@codesourcery.com> wrote:
>
> Hi!
>
> On 2022-10-18T18:14:54-0400, Lewis Hyatt via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> > [...] add a new
> > GTY option "string_length" so that gt_pch_note_object can be informed the
> > actual length it ought to use, [...]
>
> > --- a/gcc/doc/gty.texi
> > +++ b/gcc/doc/gty.texi
> > @@ -196,7 +196,26 @@ static GTY((length("reg_known_value_size"))) rtx *reg_known_value;
> >  Note that the @code{length} option is only meant for use with arrays of
> >  non-atomic objects, that is, objects that contain pointers pointing to
> >  other GTY-managed objects.  For other GC-allocated arrays and strings
> > -you should use @code{atomic}.
> > +you should use @code{atomic} or @code{string_length}.
> > +
> > +@findex string_length
> > +@item string_length ("@var{expression}")
> > +
> > +In order to simplify production of PCH, a structure member that is a plain
> > +array of bytes (an optionally @code{const} and/or @code{unsigned} @code{char
> > +*}) is treated specially by the infrastructure. Even if such an array has not
> > +been allocated in GC-controlled memory, it will still be written properly into
> > +a PCH.  The machinery responsible for this needs to know the length of the
> > +data; by default, the length is determined by calling @code{strlen} on the
> > +pointer.  The @code{string_length} option specifies an alternate way to
> > +determine the length, such as by inspecting another struct member:
> > +
> > +@smallexample
> > +struct GTY(()) non_terminated_string @{
> > +  size_t sz;
> > +  const char * GTY((string_length ("%h.sz"))) data;
> > +@};
> > +@end smallexample
>
> In preparation for another thing I'm working on, OK to push the attached
> "GTY: Explicitly reject 'string_length' option for (fields in) global variables"
> (with <https://inbox.sourceware.org/[TODO]> pointing to this message)?

OK

>
> Grüße
>  Thomas
>
>
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