Re: [PATCH 1/2] Compiler Attributes: add support for __fallthrough (gcc >= 7.1)

2018-10-22 Thread Nick Desaulniers 
On Mon, Oct 22, 2018 at 11:15 AM Bernd Petrovitsch
 wrote:
>
> Hi all!
>
> On 22/10/18 19:54, Nick Desaulniers wrote:
> > On Mon, Oct 22, 2018 at 10:50 AM Bernd Petrovitsch
> >  wrote:
> [...]
> >> PS: clang++ errors with "fallthrough annotation in unreachable code" if
> >> [[fallthrough]] is after an assert(). clang-devs there, please, the
> >> fallthrough doesn't really generated code (I hope;-).
> [...]
> > Can you send me a link to a simple reproducer in godbolt (godbolt.org)
> > and we'll take a look?
>
> Does https://godbolt.org/z/2Y4zIo do it - I'm a godbolt-newbie?

Moving the kernel folks to bcc, since we don't need to be discussing
C++ on LKML.
https://godbolt.org/z/B1fo9Z shows that this works as intended, for
cases that cannot be statically proven.  I guess I'm looking for a
more realistic code sample to show why putting a `break;` statement
there is untenable?

>
> For
>   snip  
> #include 
>
> int main(void)
> {
>   switch (1) {
>   default:
> assert(0);
> [[fallthrough]];
>   case 1:
> ;
>   }
>   return 0;
> }
>   snip  
> Just "clang++ -Wimplicit-fallthrough -Werror" it .
>
> MfG,
> Bernd
> --
> "I dislike type abstraction if it has no real reason. And saving
> on typing is not a good reason - if your typing speed is the main
> issue when you're coding, you're doing something seriously wrong."
> - Linus Torvalds



-- 
Thanks,
~Nick Desaulniers

[GIT PULL] Compiler Attributes for v4.20-rc1

2018-10-22 Thread Miguel Ojeda 
Hi Linus,

Here it is the Compiler Attributes series/tree, which tries to disentangle
the include/linux/compiler*.h headers and bring them up to date.

The patches have been in linux-next for a while, *except* the last two
from Nick which came a bit later. Since AFAIU there will be no linux-next
this week, I included them here; but let me know if you prefer
to take them out.

You may see merge conflicts from a few other trees, from what we have
seen in linux-next.

I am not sure if you followed this, so please let me know if there is
anything you don't agree with.

And welcome back!

Cheers,
Miguel

The following changes since commit 17b57b1883c1285f3d0dc2266e8f79286a7bef38:

  Linux 4.19-rc6 (2018-09-30 07:15:35 -0700)

are available in the Git repository at:

  https://github.com/ojeda/linux.git tags/compiler-attributes-for-linus-4.20-rc1

for you to fetch changes up to 1ff2fea5e30ca15752777441ecb64a169fe22e9e:

  compiler-gcc: remove comment about gcc 4.5 from unreachable() (2018-10-19 
08:47:30 +0200)


The Compiler Attributes series

This is an effort to disentangle the include/linux/compiler*.h headers
and bring them up to date.

The main idea behind the series is to use feature checking macros
(i.e. __has_attribute) instead of compiler version checks (e.g. GCC_VERSION),
which are compiler-agnostic (so they can be shared, reducing the size
of compiler-specific headers) and version-agnostic.

Other related improvements have been performed in the headers as well,
which on top of the use of __has_attribute it has amounted to a significant
simplification of these headers (e.g. GCC_VERSION is now only guarding
a few non-attribute macros).

This series should also help the efforts to support compiling the kernel
with clang and icc. A fair amount of documentation and comments have also
been added, clarified or removed; and the headers are now more readable,
which should help kernel developers in general.

The series was triggered due to the move to gcc >= 4.6. In turn, this series
has also triggered Sparse to gain the ability to recognize __has_attribute
on its own.

Finally, the __nonstring variable attribute series has been also applied
on top; plus two related patches from Nick Desaulniers for unreachable()
that came a bit afterwards.


Miguel Ojeda (15):
  Compiler Attributes: remove unused attributes
  Compiler Attributes: always use the extra-underscores syntax
  Compiler Attributes: remove unneeded tests
  Compiler Attributes: homogenize __must_be_array
  Compiler Attributes: remove unneeded sparse (__CHECKER__) tests
  Compiler Attributes: add missing SPDX ID in compiler_types.h
  Compiler Attributes: use feature checks instead of version checks
  Compiler Attributes: KENTRY used twice the "used" attribute
  Compiler Attributes: remove uses of __attribute__ from compiler.h
  Compiler Attributes: add Doc/process/programming-language.rst
  Compiler Attributes: add MAINTAINERS entry
  Compiler Attributes: add support for __nonstring (gcc >= 8)
  Compiler Attributes: enable -Wstringop-truncation on W=1 (gcc >= 8)
  Compiler Attributes: auxdisplay: panel: use __nonstring
  Compiler Attributes: ext4: remove local __nonstring definition

ndesaulni...@google.com (2):
  compiler.h: update definition of unreachable()
  compiler-gcc: remove comment about gcc 4.5 from unreachable()

 Documentation/process/index.rst|   1 +
 Documentation/process/programming-language.rst |  45 +
 MAINTAINERS|   5 +
 drivers/auxdisplay/panel.c |   7 +-
 fs/ext4/ext4.h |   9 -
 include/linux/compiler-clang.h |   5 -
 include/linux/compiler-gcc.h   |  74 +--
 include/linux/compiler-intel.h |   9 -
 include/linux/compiler.h   |  24 +--
 include/linux/compiler_attributes.h| 258 +
 include/linux/compiler_types.h | 101 ++
 scripts/Makefile.extrawarn |   1 +
 12 files changed, 345 insertions(+), 194 deletions(-)
 create mode 100644 Documentation/process/programming-language.rst
 create mode 100644 include/linux/compiler_attributes.h