Re: [Xen-devel] [PATCH 1/6] xen/build: Allow the use of C freestanding headers

[Tim Deegan <tim@xxxxxxx>]

At 12:24 +0100 on 22 Jun (1466598248), Andrew Cooper wrote:
> The C standard defines two types of conforming implementation; hosted and
> freestanding.  A subset of the standard headers are the freestanding headers,
> requiring no library support at all to use, and therefore usable by Xen.
> 
> Unfortunately, -nostdinc is an overly large switch, and there is no
> alternative to only permit inclusion of the freestanding headers.  Removing it
> is unfortunate, as we lose the protection it offers, but anyone who does try
> to use other parts of the standard library will still fail to link.

I'm afraid I don't think this is a good idea:
 - Leaving the standard include path around in the Xen build means
   that the build may differ based on what (unrelated) libraries are
   installed on the build machines.
 - There are plenty of ways for an unexpected header to break things
   that don't fail at link time, e.g. macros and inlines.
 - "Freestanding" headers can bring in quite a lot of unrelated cruft.
   See Jan's email about linux/glibc, and I remember seeing similar
   things on solaris and *BSD when I tidied up stdarg.h. E.g. looking
   at two machines I'm working on today, on one of them,
   #include <limits.h> defines __packed, and on the other it does not.

Since what we have already works fine for all the compilers we
support, I think it ain't broke and we shouldn't fix it.

Nacked-by: Tim Deegan <tim@xxxxxxx>

OTOH, I am in favour of s/bool_t/bool/g, at least wherever field size
is not an issue, and I can see an argument for moving the type and
limits definitions into files called stdint.h and limits.h.

Cheers,

Tim.

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