[PATCH v2] drm/fourcc: introduce DRM_FOURCC_STANDALONE guard

[James Park]

On Thu, Feb 4, 2021 at 9:37 AM James Park <james.park at lagfreegames.com> wrote:
>
> On Thu, Feb 4, 2021 at 3:37 AM Emil Velikov <emil.l.velikov at gmail.com> wrote:
> >
> > Currently, the drm_fourcc.h header depends on drm.h for __u32 and __u64.
> > At the same time drm.h pulls a lot of unneeded symbols.
> >
> > Add new guard DRM_FOURCC_STANDALONE, which when set will use local
> > declaration of said symbols.
> >
> > When used on linux - we pull linux/types.h which is used either way.
> > On other platforms, BSDs et al, we need a couple of typedefs.
> >
> > Since those can trigger a warning in some corner-cases*, add some GCC
> > magic to silence them. Note that incorrect type redefinitions will still
> > be flagged, and the GCC pragma is ignored by other compilers.
> >
> > *Corner-case:
> > If one sets DRM_FOURCC_STANDALONE and compiles with C99 or earlier while
> > also using -pedantic _and_ the header lives outside of the standard
> > /usr/include (like BSDs normally do).
> >
> > v2:
> >  - Add corner-case handling, based on popular demand.
> >
> > Cc: James Park <james.park at lagfreegames.com>
> > Cc: Pekka Paalanen <pekka.paalanen at collabora.com>
> > Cc: Simon Ser <contact at emersion.fr>
> > Signed-off-by: Emil Velikov <emil.l.velikov at gmail.com>
> > ---
> >  include/uapi/drm/drm.h        | 10 ++++++++++
> >  include/uapi/drm/drm_fourcc.h | 29 +++++++++++++++++++++++++++++
> >  2 files changed, 39 insertions(+)
> >
> > diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
> > index 808b48a93330..cd78950e05ce 100644
> > --- a/include/uapi/drm/drm.h
> > +++ b/include/uapi/drm/drm.h
> > @@ -53,6 +53,15 @@ typedef unsigned int drm_handle_t;
> >  #include <stdint.h>
> >  #include <sys/ioccom.h>
> >  #include <sys/types.h>
> > +
> > +/*
> > + * When using C99 -pedantic the typedefs will trigger a warning.
> > + * If the header is considered a system one (-isystem) those will be
> > + * ignored, yet on the target platforms BSDs, et al - the headers live
> > + * in a non-system location.
> > + */
> > +#pragma GCC diagnostic push
> > +#pragma GCC diagnostic ignored "-Wpedantic"
> >  typedef int8_t   __s8;
> >  typedef uint8_t  __u8;
> >  typedef int16_t  __s16;
> > @@ -63,6 +72,7 @@ typedef int64_t  __s64;
> >  typedef uint64_t __u64;
> >  typedef size_t   __kernel_size_t;
> >  typedef unsigned long drm_handle_t;
> > +#pragma GCC diagnostic pop
> >
> >  #endif
> >
> > diff --git a/include/uapi/drm/drm_fourcc.h b/include/uapi/drm/drm_fourcc.h
> > index 6f0628eb13a6..84a1f96cc4ef 100644
> > --- a/include/uapi/drm/drm_fourcc.h
> > +++ b/include/uapi/drm/drm_fourcc.h
> > @@ -24,7 +24,36 @@
> >  #ifndef DRM_FOURCC_H
> >  #define DRM_FOURCC_H
> >
> > +/*
> > + * Define DRM_FOURCC_STANDALONE you're interested only FOURCC and do not want
> > + * to pull drm.h into your application.
> > + */
> > +#ifdef DRM_FOURCC_STANDALONE
> > +#if defined(__linux__)
> > +
> > +#include <linux/types.h>
> > +
> > +#else /* One of the BSDs */
> > +
> > +#include <stdint.h>
> > +
> > +/*
> > + * When using C99 -pedantic the typedefs will trigger a warning.
> > + * If the header is considered a system one (-isystem) those will be
> > + * ignored, yet on the target platforms BSDs, et al - the headers live
> > + * in a non-system location.
> > + */
> > +#pragma GCC diagnostic push
> > +#pragma GCC diagnostic ignored "-Wpedantic"
> > +typedef uint32_t __u32;
> > +typedef uint64_t __u64;
> > +#pragma GCC diagnostic pop
> > +
> > +#endif /* __linux __ */
> > +
> > +#else
> >  #include "drm.h"
> > +#endif /* DRM_FOURCC_STANDALONE */
> >
> >  #if defined(__cplusplus)
> >  extern "C" {
> > --
> > 2.30.0
> >
>
> I remember reading GCC diagnostic push/pop requires a recent enough
> compiler version to be supported, which is pretty old, but I don't
> know how old is old enough for Linux headers:
> https://github.com/protocolbuffers/protobuf/issues/4156
>
> Testing snippets in godbolt, I think the pragmas need to be wrapped. MSVC says:
>
> warning C4068: unknown pragma 'GCC'
>
> Also, Clang seems to want -Wtypedef-redefinition, not -Wpedantic. GCC
> complains it doesn't know what -Wtypedef-redefinition is, so that
> would also need to be wrapped.

If we're already conceding copy/paste, then how about inlining my
previous header?

#ifndef DRM_BASIC_TYPES_DEFINED
#define DRM_BASIC_TYPES_DEFINED
// Sync modifications between drm.h and drm_fourcc.h
...
#endif

No compiler games. Valid on all flavors of C (I think).