Re: 27bb4de72b * Port cleanup attribute to Oracle Studio 12.5

[Philipp Stephani <p.stephani2@gmail.com>]

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Paul Eggert <eggert@cs.ucla.edu> schrieb am Do., 15. Juni 2017 um 20:46 Uhr:

> On 06/15/2017 05:54 AM, Philipp Stephani wrote:
> > I've considered a couple of options. I think the simplest and most
> > portable one would be to compile as C++, which has destructors built
> > into the language.
>
> That would require some autoconf and makefile hacking, but it would
> work. That is, if modules are enabled, and __attribute__ ((cleanup)) is
> not available but a C++ compiler is available, then the build process
> could use the C++ compiler. Admittedly this is low priority.
>

Alternatively, we might even compile emacs-modules.c as C++
unconditionally. I guess by now every system that has a C compiler and
supports shared libraries also has a C++ compiler.


>
> > How about using #pragma clang diagnostic push/pop/ignore to ignore the
> > warnings in the specific statements where they arise and we know that
> > they are false positives? I'd much prefer that over disabling them
> > globally in configure, because most of the time the warnings are useful.
>
> Although many warnings are useful, in my experience these particular
> warnings are not useful for Emacs. That is, the hassle they cause by
> false alarms costs more than the benefits of actual bugs that they fix.
> It's OK to disable such warnings globally.
>
> >
> >     And I'm still puzzled as to why you're getting the Clang warnings
> >     but I
> >     am not. Are you using an older Clang? Are you passing it extra
> warning
> >     options?
> >
> >
> > I'm using the Apple fork on macOS. It's mostly identical to upstream
> > Clang and compiles Emacs just fine, but it is a fork and not 100%
> > identical. I also get some of the warnings only when building with -O3
> > (haven't checked other optimization levels).
>
> I just now applied the attached patch, configured with:
>
> ./configure --enable-gcc-warnings CC=clang CFLAGS='-O3'
>
> and had no problems on Fedora 25. If you have a problem with this patch,
> can you please send relevant output from 'clang --version' and 'make
> V=1'?


On macOS 10.12.5, current master, and the rlim_t patch reverted:

$ git rev-parse HEAD
1ac8c9bb9b6ba44585ed68b03ebbce659a777041

$ gcc -c  -Demacs  -I. -I. -I../lib -I../lib   -I/usr/X11/include
 -I/usr/local/Cellar/dbus/1.10.18/include/dbus-1.0
-I/usr/local/Cellar/dbus/1.10.18/lib/dbus-1.0/include           -MMD -MF
deps/emacs.d -MP  -I/usr/local/Cellar/gnutls/3.5.13/include
-I/usr/local/Cellar/nettle/3.3/include
-I/usr/local/Cellar/libtasn1/4.12/include
-I/usr/local/Cellar/p11-kit/0.23.7/include/p11-kit-1    -Wno-switch
-Wno-tautological-constant-out-of-range-compare -Wno-pointer-sign
-Wno-string-plus-int -Wno-unknown-attributes -ggdb3 -O0  emacs.c

*emacs.c:835:12: **warning: **comparison of 0 <= unsigned expression is
always true*

*      [-Wtautological-compare]*

      && 0 <= rlim.rlim_cur && rlim.rlim_cur <= LONG_MAX)

*         ~ ^  ~~~~~~~~~~~~~*

*emacs.c:869:10: **warning: **comparison of 0 <= unsigned expression is
always true*

*      [-Wtautological-compare]*

          if (0 <= rlim.rlim_max && rlim.rlim_max < newlim)

*              ~ ^  ~~~~~~~~~~~~~*

2 warnings generated.


$ ./config.status --config

'--with-modules' '--without-xml2' '--without-pop' '--with-mailutils'
'--enable-checking' '--enable-check-lisp-object-type'
'MAKEINFO=/usr/local/opt/texinfo/bin/makeinfo' 'CFLAGS=-ggdb3 -O0'


(i.e. this doesn't even need --enable-gcc-warnings)



The other case, same repo version, but the other commit reverted:


$ make -C lib-src make-docfile V=1

gcc   -Wno-switch -Wno-tautological-constant-out-of-range-compare
-Wno-pointer-sign -Wno-string-plus-int -Wno-unknown-attributes  -I.
-I../src -I../lib -I. -I./../src -I./../lib    -O3 -save-temps
make-docfile.c  ../lib/libgnu.a  -o make-docfile

*make-docfile.c:227:19: **warning: **equality comparison with extraneous
parentheses*

*      [-Wparentheses-equality]*

      if (((*tmp) == '/'))

*           ~~~~~~~^~~~~~*

*make-docfile.c:227:19: **note: *remove extraneous parentheses around the
comparison

      to silence this warning

      if (((*tmp) == '/'))

*          ~       ^     ~*

*make-docfile.c:227:19: **note: *use '=' to turn this equality comparison
into an

      assignment

      if (((*tmp) == '/'))

*                  ^~*

                  =

1 warning generated.


$ ./config.status --config

'--with-modules' '--without-xml2' '--without-pop' '--with-mailutils'
'--enable-checking' '--enable-check-lisp-object-type'
'MAKEINFO=/usr/local/opt/texinfo/bin/makeinfo' 'CFLAGS=-O3 -save-temps'


Note that the -save-temps is crucial here, without it the compiler doesn't
look at the preprocessed output.

It's weird that -save-temps generates more warnings, but GCC has similar
issues (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57201). -save-temps
also generates tons of warnings for other files, even without
--enable-gcc-warnings.

Not sure what to do about the -save-temps problem. Maybe that's just
something to document somewhere, because there seems to be little we can do
about it.


$ gcc --version

Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr
--with-gxx-include-dir=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk/usr/include/c++/4.2.1

Apple LLVM version 8.1.0 (clang-802.0.42)

Target: x86_64-apple-darwin16.6.0

Thread model: posix

InstalledDir:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

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