Re: [PATCH] Add a character size parameter to c_strlen/get_range_strlen

[Martin Sebor <msebor at gmail dot com>]

On 08/21/2018 09:44 AM, Joseph Myers wrote:
> On Tue, 21 Aug 2018, Martin Sebor wrote:
>
> > Sure, but the only valid argument to %ls is wchar_t*.  Passing
> > it something else is undefined.
>
> Well, (wchar_t *)"something\0\0\0\0" would be OK given
> -fno-strict-aliasing and if you know the alignment is OK.  Do we have that
> information about the type cast to, as opposed to the type of the string
> constant, at this point?

In the simple cases like the one above the cast is gone.  Only
in some more involved cases is the type of the argument preserved.
I responded to Jeff with one such example here:

  https://gcc.gnu.org/ml/gcc-patches/2018-08/msg01296.html

If supporting (wchar_t *)"...\0\0\0\0" with %ls is viewed as
important (despite it being undefined) then the function does
need an ELTSIZE argument so it knows what to count.  In that
event, in order to detect the problem cases we have been
discussing (missing nuls and mismatched argument types),
the function it must not fail when ELTSIZE is not equal
to the size of actual array element.  Instead, it needs to
return the element type to the caller which then needs to
do the validation and issue a diagnostic.

Martin