[RFC] UAPI: Check headers by compiling all together as C++

[RFC] UAPI: Check headers by compiling all together as C++

[David Howells]

Here's a set of patches that inserts a step into the build process to make
sure that the UAPI headers can all be built together with C++ (if the
compiler being used supports C++).  All but the final patch perform fixups,
including:

 (1) Fix member names that conflict with C++ reserved words by providing
     alternates that can be used anywhere.  An anonymous union is used so
     that that the conflicting name is still available outside of C++.

 (2) Fix the use of flexible arrays in structs that get embedded (which is
     illegal in C++).

 (3) Remove the use of internal kernel structs in UAPI structures.

 (4) Fix symbol collisions.

 (5) Replace usage of u32 and co. with __u32 and co.

 (6) Fix use of sparsely initialised arrays (which g++ doesn't implement).

 (7) Remove some use of PAGE_SIZE since this isn't valid outside of the
     kernel.

And lastly:

 (8) Compile all of the UAPI headers (with a few exceptions) together as
     C++ to catch new errors occurring as part of the regular build
     process.

The patches can also be found here:

	http://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/log/?h=uapi-check

Thanks,
David
---
David Howells (11):
      UAPI: drm: Fix use of C++ keywords as structural members
      UAPI: keys: Fix use of C++ keywords as structural members
      UAPI: virtio_net: Fix use of C++ keywords as structural members
      UAPI: bcache: Fix use of embedded flexible array
      UAPI: coda: Don't use internal kernel structs in UAPI
      UAPI: netfilter: Fix symbol collision issues
      UAPI: nilfs2: Fix use of undefined byteswapping functions
      UAPI: sound: Fix use of u32 and co. in UAPI headers
      UAPI: ndctl: Fix g++-unsupported initialisation in headers
      UAPI: ndctl: Remove use of PAGE_SIZE
      UAPI: Check headers build for C++


 Makefile                                          |    1 
 include/linux/ndctl.h                             |   22 ++++
 include/uapi/drm/i810_drm.h                       |    7 +
 include/uapi/drm/msm_drm.h                        |    7 +
 include/uapi/linux/bcache.h                       |    2 
 include/uapi/linux/coda_psdev.h                   |    4 +
 include/uapi/linux/keyctl.h                       |    7 +
 include/uapi/linux/ndctl.h                        |   20 ++-
 include/uapi/linux/netfilter/nfnetlink_cthelper.h |    2 
 include/uapi/linux/netfilter_ipv4/ipt_ECN.h       |    9 --
 include/uapi/linux/nilfs2_ondisk.h                |   21 ++--
 include/uapi/linux/virtio_net.h                   |    7 +
 include/uapi/sound/skl-tplg-interface.h           |  106 +++++++++---------
 scripts/headers-c++.sh                            |  124 +++++++++++++++++++++
 14 files changed, 255 insertions(+), 84 deletions(-)
 create mode 100644 include/linux/ndctl.h
 create mode 100755 scripts/headers-c++.sh

[PATCH 01/11] UAPI: drm: Fix use of C++ keywords as structural members

[David Howells]

The i810 and msm drm drivers use C++ keywords as structural members.  Fix
this by inserting an anonymous union that provides an alternative name and
then hide the reserved name in C++.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Rob Clark <robdclark@gmail.com>
cc: David Airlie <airlied@linux.ie>
cc: linux-arm-msm@vger.kernel.org
cc: dri-devel@lists.freedesktop.org
cc: freedreno@lists.freedesktop.org
---

 include/uapi/drm/i810_drm.h |    7 ++++++-
 include/uapi/drm/msm_drm.h  |    7 ++++++-
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/uapi/drm/i810_drm.h b/include/uapi/drm/i810_drm.h
index d285d5e72e6a..617d79ec3fc5 100644
--- a/include/uapi/drm/i810_drm.h
+++ b/include/uapi/drm/i810_drm.h
@@ -266,7 +266,12 @@ typedef struct _drm_i810_copy_t {
 #define PR_MASK              (0x7<<18)
 
 typedef struct drm_i810_dma {
-	void *virtual;
+	union {
+#ifndef __cplusplus
+		void *virtual;
+#endif
+		void *_virtual;
+	};
 	int request_idx;
 	int request_size;
 	int granted;
diff --git a/include/uapi/drm/msm_drm.h b/include/uapi/drm/msm_drm.h
index c06d0a5bdd80..e99bab72d58c 100644
--- a/include/uapi/drm/msm_drm.h
+++ b/include/uapi/drm/msm_drm.h
@@ -148,7 +148,12 @@ struct drm_msm_gem_cpu_fini {
  */
 struct drm_msm_gem_submit_reloc {
 	__u32 submit_offset;  /* in, offset from submit_bo */
-	__u32 or;             /* in, value OR'd with result */
+	union {
+#ifndef __cplusplus
+		__u32 or;	/* in, value OR'd with result */
+#endif
+		__u32 _or;	/* in, value OR'd with result */
+	};
 	__s32 shift;          /* in, amount of left shift (can be negative) */
 	__u32 reloc_idx;      /* in, index of reloc_bo buffer */
 	__u64 reloc_offset;   /* in, offset from start of reloc_bo */

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Re: [RFC] UAPI: Check headers by compiling all together as C++

[Greg KH]

On Wed, Sep 05, 2018 at 04:54:27PM +0100, David Howells wrote:
> 
> Here's a set of patches that inserts a step into the build process to make
> sure that the UAPI headers can all be built together with C++ (if the
> compiler being used supports C++).  All but the final patch perform fixups,
> including:

Wait, why do we care?  What has recently changed to start to directly
import kernel uapi files into C++ code?

And if userspace wants to do this, can't they do the C namespace trick
themselves when they do the import?  That must be how they are doing it
today, right?

thanks,

greg k-h

Re: [RFC] UAPI: Check headers by compiling all together as C++

[Yann Droneaud]

Hi,

Le mercredi 05 septembre 2018 à 18:55 +0200, Greg KH a écrit :
> On Wed, Sep 05, 2018 at 04:54:27PM +0100, David Howells wrote:
> > 
> > Here's a set of patches that inserts a step into the build process to make
> > sure that the UAPI headers can all be built together with C++ (if the
> > compiler being used supports C++).  All but the final patch perform fixups,
> > including:
> 
> Wait, why do we care?  What has recently changed to start to directly
> import kernel uapi files into C++ code?
> 
> And if userspace wants to do this, can't they do the C namespace trick
> themselves when they do the import?  That must be how they are doing it
> today, right?
> 

They can't.


Adding extern "C" { } doesn't magically make "class" a non keyword.
Even if it was the case, writing C++ code using whatever->class would
probably broke because class is a keyword in C++.

-- 
Yann Droneaud
OPTEYA


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Re: [RFC] UAPI: Check headers by compiling all together as C++

[Michael S. Tsirkin]

On Wed, Sep 05, 2018 at 07:33:38PM +0200, Yann Droneaud wrote:
> Hi,
> 
> Le mercredi 05 septembre 2018 à 18:55 +0200, Greg KH a écrit :
> > On Wed, Sep 05, 2018 at 04:54:27PM +0100, David Howells wrote:
> > > 
> > > Here's a set of patches that inserts a step into the build process to make
> > > sure that the UAPI headers can all be built together with C++ (if the
> > > compiler being used supports C++).  All but the final patch perform fixups,
> > > including:
> > 
> > Wait, why do we care?  What has recently changed to start to directly
> > import kernel uapi files into C++ code?
> > 
> > And if userspace wants to do this, can't they do the C namespace trick
> > themselves when they do the import?  That must be how they are doing it
> > today, right?
> > 
> 
> They can't.
> 
> 
> Adding extern "C" { } doesn't magically make "class" a non keyword.
> Even if it was the case, writing C++ code using whatever->class would
> probably broke because class is a keyword in C++.

I think it's a bug in the language TBH.

> -- 
> Yann Droneaud
> OPTEYA
> 
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Re: [RFC] UAPI: Check headers by compiling all together as C++

[Jan Engelhardt]

On Wednesday 2018-09-05 18:55, Greg KH wrote:

>On Wed, Sep 05, 2018 at 04:54:27PM +0100, David Howells wrote:
>> 
>> Here's a set of patches that inserts a step into the build process to make
>> sure that the UAPI headers can all be built together with C++ (if the
>> compiler being used supports C++).  All but the final patch perform fixups,
>> including:
>
>Wait, why do we care?  What has recently changed to start to directly
>import kernel uapi files into C++ code?

With C++11, C++ has become a much nicer language to use (for userspace, anyway).

>And if userspace wants to do this, can't they do the C namespace trick
>themselves when they do the import?

The only trick is to use an extra C source file and extensively wrap things.

Re: [RFC] UAPI: Check headers by compiling all together as C++

[Yann Droneaud]

Le mercredi 05 septembre 2018 à 19:33 +0200, Yann Droneaud a écrit :
> Le mercredi 05 septembre 2018 à 18:55 +0200, Greg KH a écrit :
> > On Wed, Sep 05, 2018 at 04:54:27PM +0100, David Howells wrote:
> > > 
> > > Here's a set of patches that inserts a step into the build
> > > process to make
> > > sure that the UAPI headers can all be built together with C++ (if
> > > the
> > > compiler being used supports C++).  All but the final patch
> > > perform fixups,
> > > including:
> > 
> > Wait, why do we care?  What has recently changed to start to
> > directly
> > import kernel uapi files into C++ code?
> > 
> > And if userspace wants to do this, can't they do the C namespace
> > trick
> > themselves when they do the import?  That must be how they are
> > doing it
> > today, right?
> > 
> 
> They can't.
> 
> 
> Adding extern "C" { } doesn't magically make "class" a non keyword.
> Even if it was the case, writing C++ code using whatever->class would
> probably broke because class is a keyword in C++.
> 

For the record, libX11 has to handle the kink pf issue with C++
keyword:


https://gitlab.freedesktop.org/xorg/lib/libx11/blob/733f64bfeb311c1d040b2f751bfdef9c9d0f89ef/include/X11/Xlib.h#L227

typedef struct {
	XExtData *ext_data;	/* hook for extension to hang data */
	VisualID visualid;	/* visual id of this visual */
#if defined(__cplusplus) || defined(c_plusplus)
	int c_class;		/* C++ class of screen (monochrome, etc.) */
#else
	int class;		/* class of screen (monochrome, etc.) */
#endif
	unsigned long red_mask, green_mask, blue_mask;	/* mask values */
	int bits_per_rgb;	/* log base 2 of distinct color values */
	int map_entries;	/* color map entries */
} Visual;


Regards.

-- 
Yann Droneaud
OPTEYA


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[RFC] UAPI: Check headers by compiling all together as C++

[David Howells]

Here's a set of patches that inserts a step into the build process to make
sure that the UAPI headers can all be built together with C++ (if the
compiler being used supports C++).

Note that it's based on a commit from the sound tree to fix usage of u32
and co..

Most of the patches perform fixups, including:

 (1) Fix member names that conflict with C++ reserved words by providing
     alternates that can be used anywhere.  An anonymous union is used so
     that that the conflicting name is still available outside of C++.

 (2) Fix the use of flexible arrays in structs that get embedded (which is
     illegal in C++).

 (3) Remove the use of internal kernel structs in UAPI structures.

 (4) Fix symbol collisions.

 (5) Fix use of sparsely initialised arrays (which g++ doesn't implement).

 (6) Remove some use of PAGE_SIZE since this isn't valid outside of the
     kernel.

There's also:

 (7) Move the coda_psdev.h header file to fs/coda/.

And lastly:

 (8) Compile all of the UAPI headers (with a few exceptions) together as
     C++ to catch new errors occurring as part of the regular build
     process.

Changes for v2:

 - Merge commit from sound tree to fix u32 usage issues
 - Use a switch to fix sparse array initialisation
 - Simplify nilfs2 by performing bitwise ops in LE space not CPU space
 - Handle conflicting fix to use of 'private' in keyctl.h
 - Move kernel internal coda bits to coda internal headers
 - Move coda_psdev.h header to fs/coda/.

The patches can also be found here:

	http://git.kernel.org/cgit/linux/kernel/git/dhowells/linux-fs.git/log/?h=uapi-check

Thanks,
David
---
David Howells (11):
      UAPI: drm: Fix use of C++ keywords as structural members
      UAPI: keys: Fix use of C++ keywords as structural members
      UAPI: virtio_net: Fix use of C++ keywords as structural members
      UAPI: bcache: Fix use of embedded flexible array
      UAPI: coda: Move kernel internals out of public view
      coda: Move internal defs out of include/linux/
      UAPI: netfilter: Fix symbol collision issues
      UAPI: nilfs2: Fix use of undefined byteswapping functions
      UAPI: ndctl: Fix g++-unsupported initialisation in headers
      UAPI: ndctl: Remove use of PAGE_SIZE
      UAPI: Check headers build for C++


 Makefile                                          |    1 
 fs/coda/cache.c                                   |    2 
 fs/coda/cnode.c                                   |    2 
 fs/coda/coda_linux.c                              |    2 
 fs/coda/coda_psdev.h                              |   88 +++++++++++++++
 fs/coda/dir.c                                     |    2 
 fs/coda/file.c                                    |    3 -
 fs/coda/inode.c                                   |    2 
 fs/coda/pioctl.c                                  |    3 -
 fs/coda/psdev.c                                   |    3 -
 fs/coda/symlink.c                                 |    3 -
 fs/coda/upcall.c                                  |    2 
 include/linux/coda_psdev.h                        |   72 ------------
 include/linux/ndctl.h                             |   22 ++++
 include/uapi/drm/i810_drm.h                       |    7 +
 include/uapi/drm/msm_drm.h                        |    7 +
 include/uapi/linux/bcache.h                       |    2 
 include/uapi/linux/coda_psdev.h                   |   18 ---
 include/uapi/linux/keyctl.h                       |    7 +
 include/uapi/linux/ndctl.h                        |   52 ++++-----
 include/uapi/linux/netfilter/nfnetlink_cthelper.h |    2 
 include/uapi/linux/netfilter_ipv4/ipt_ECN.h       |    9 --
 include/uapi/linux/nilfs2_ondisk.h                |   28 ++---
 include/uapi/linux/virtio_net.h                   |    7 +
 scripts/headers-c++.sh                            |  124 +++++++++++++++++++++
 25 files changed, 304 insertions(+), 166 deletions(-)
 create mode 100644 fs/coda/coda_psdev.h
 delete mode 100644 include/linux/coda_psdev.h
 create mode 100644 include/linux/ndctl.h
 create mode 100755 scripts/headers-c++.sh

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