Paul Eggert wrote:
> > Is that use of -Wextra an experiment, or do you want to use it always?
>
> Oh, it was just an experiment.
>
> > I'm asking because some the warnings that it enables are undesired, IMO,
>
> Quite right.
Glad to hear this.
I went through all warnings I could get from GCC 13 and formulated three
recommended sets of warnings for Gnulib; see the patch below. (I essentially
used the same approach as we do with the 'manywarnings' module. But rather
than hardwiring some "preferred" set of warning options into gnulib-tool's
--create-testdir command, I find it better to leave the choice to the
individual developer.)
> I expect that many of the warnings you found are false alarms, and that
> it's low priority to look into this.
It really depends on the warning category. Some of the warnings I fixed
yesterday were really helpful:
- for maintainability: -Wshadow
- for finishing unfinished code: -Wunused-value
- for POSIX compliance: -Wanalyzer-unsafe-call-within-signal-handler
- other: -Wanalyzer-allocation-size
> I adjusted test code for the "xxx
> is unused" warnings only because it was easy in the context of coreutils
> and the warnings I found by the experiment were arguably useful.
The various forms of the 'main' declaration are _arguable_, yes.
main ()
main (_GL_UNUSED int argc, _GL_UNUSED char *argv[])
main (_GL_UNUSED int argc, char *argv[])
main (int argc, _GL_UNUSED char *argv[])
main (int argc, char *argv[])
To me, that's clutter: it distracts the attention when I'm reading the code.
2023-09-05 Bruno Haible <br...@clisp.org>
Add info about recommended warning options.
* HACKING: New section "Warning Options".
================================ >> HACKING ================================
Warning Options
===============
For packages that use Gnulib, we recommend to use the 'warnings' or
'manywarnings' module, as documented in
https://www.gnu.org/software/gnulib/manual/html_node/warnings.html
https://www.gnu.org/software/gnulib/manual/html_node/manywarnings.html
When building Gnulib testdirs, e.g. when preparing a Gnulib patch,
there are three possible approaches:
* The simplest approach, which warns about the most common mistakes, is to
use GCC's -Wall option, both for C and C++ compilation units. Just set
$ ./configure CPPFLAGS="-Wall"
$ make
You should generally fix all compiler warnings that you see from this
approach.
* If you are developing on a glibc system and have GCC version 13 binaries
available, here's a recipe that will find more mistakes, but is nearly
as easy to use. Here, different warning options are needed for C and
for C++:
$ WARN_GCC13="-fanalyzer -Wall -Warith-conversion -Wcast-align=strict
-Wdate-time -Wdisabled-optimization -Wduplicated-cond -Wextra
-Wformat-signedness -Winit-self -Winvalid-pch -Wlogical-op
-Wmissing-include-dirs -Wopenmp-simd -Woverlength-strings -Wpacked
-Wpointer-arith -Wstrict-overflow -Wsuggest-final-methods -Wsuggest-final-types
-Wsync-nand -Wsystem-headers -Wtrampolines -Wuninitialized -Wunknown-pragmas
-Wunsafe-loop-optimizations -Wvariadic-macros -Wvector-operation-performance
-Wwrite-strings -Warray-bounds=2 -Wattribute-alias=2 -Wformat-overflow=2
-Wformat-truncation=2 -Wshift-overflow=2 -Wunused-const-variable=2
-Wvla-larger-than=4031 -Wno-empty-body -Wno-analyzer-allocation-size
-Wno-analyzer-fd-double-close -Wno-analyzer-double-fclose
-Wno-analyzer-double-free -Wno-analyzer-fd-leak
-Wno-analyzer-fd-use-after-close -Wno-analyzer-fd-use-without-check
-Wno-analyzer-free-of-non-heap -Wno-analyzer-malloc-leak
-Wno-analyzer-mismatching-deallocation -Wno-analyzer-null-argument
-Wno-analyzer-null-dereference -Wno-analyzer-out-of-bounds
-Wno-analyzer-possible-null-argument -Wno-analyzer-possible-null-dereference
-Wno-analyzer-use-after-free -Wno-analyzer-use-of-pointer-in-stale-stack-frame
-Wno-analyzer-use-of-uninitialized-value -Wno-analyzer-va-arg-type-mismatch
-Wno-attribute-warning -Wno-cast-align -Wno-clobbered -Wno-dangling-pointer
-Wno-format -Wno-implicit-fallthrough -Wno-maybe-uninitialized
-Wno-missing-field-initializers -Wno-restrict -Wno-sign-compare -Wno-switch
-Wno-type-limits -Wno-unused-parameter"
$ WARN_CFLAGS_GCC13="$WARN_GCC13 -Wnested-externs -Wshadow=local
-Wno-discarded-qualifiers"
$ WARN_CXXFLAGS_GCC13="$WARN_GCC13 -Wno-cpp"
$ ./configure CFLAGS="-O2 -g $WARN_CFLAGS_GCC13" CXXFLAGS="-O2 -g
$WARN_CXXFLAGS_GCC13"
$ make
You should generally fix all compiler warnings that you see from this
approach, or report when this approach produced a pointless warning
(so that we can fix the value of WARN_GCC13 above).
* If you are developing on a glibc system and have GCC version 13 binaries
available: Here's a recipe that will find even more mistakes, but it
requires that you are willing to filter out and ignore pointless warnings.
$ WARN_GCC13="-fanalyzer -Wall -Warith-conversion -Wcast-align=strict
-Wdate-time -Wdisabled-optimization -Wduplicated-cond -Wextra
-Wformat-signedness -Winit-self -Winvalid-pch -Wlogical-op
-Wmissing-include-dirs -Wnull-dereference -Wopenmp-simd -Woverlength-strings
-Wpacked -Wpointer-arith -Wstrict-overflow -Wsuggest-attribute=format
-Wsuggest-final-methods -Wsuggest-final-types -Wsync-nand -Wsystem-headers
-Wtrampolines -Wuninitialized -Wunknown-pragmas -Wunsafe-loop-optimizations
-Wvariadic-macros -Wvector-operation-performance -Wwrite-strings
-Warray-bounds=2 -Wattribute-alias=2 -Wformat-overflow=2 -Wformat=2
-Wformat-truncation=2 -Wimplicit-fallthrough=5 -Wshift-overflow=2
-Wunused-const-variable=2 -Wvla-larger-than=4031 -Wno-empty-body
-Wno-analyzer-double-fclose -Wno-analyzer-double-free
-Wno-analyzer-free-of-non-heap -Wno-analyzer-malloc-leak
-Wno-analyzer-null-argument -Wno-analyzer-null-dereference
-Wno-analyzer-use-after-free -Wno-attribute-warning -Wno-cast-align
-Wno-clobbered -Wno-format-nonliteral -Wno-sign-compare -Wno-type-limits
-Wno-unused-parameter"
$ WARN_CFLAGS_GCC13="$WARN_GCC13 -Wnested-externs -Wshadow=local"
$ WARN_CXXFLAGS_GCC13="$WARN_GCC13 -Wno-cpp"
$ ./configure CFLAGS="-O2 -g $WARN_CFLAGS_GCC13" CXXFLAGS="-O2 -g
$WARN_CXXFLAGS_GCC13"
$ make
With this approach, use your own judgement whether to fix warnings
arising from your new code or not.
Do *not* submit patches to silence warnings from existing code:
- For these warnings, often the cure will be worse than the disease.
- Some of the warnings are false positives. Rather than silencing
these warnings, we prefer to report them in the GCC bug tracker
and wait until they are fixed in a future GCC release.
