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Re: [libvirt] [PATCH 1/6] Use gnulib's manywarnings & warnings modules



On Mon, Apr 04, 2011 at 02:29:06PM -0600, Eric Blake wrote:
> On 04/04/2011 10:19 AM, Daniel P. Berrange wrote:
> > Remove custom code for checking compiler warnings, using
> > gl_WARN_ADD instead. Don't list all flags ourselves, use
> > gnulib's gl_MANYWARN_ALL_GCC to get all possible GCC flags,
> > then turn off the ones we don't want yet.
> > 
> > * acinclude.m4: Rewrite to use gl_WARN_ADD and gl_MANYWARN_ALL_GCC
> > * bootstrap.conf: Add warnings & manywarnings
> > * configure.ac: Switch to gl_WARN_ADD
> > * m4/compiler-flags.m4: Obsoleted by gl_WARN_ADD
> > ---
> >  acinclude.m4         |  158 +++++++++++++++++++++++++++-----------------------
> >  bootstrap.conf       |    2 +
> >  configure.ac         |   15 +++--
> >  m4/compiler-flags.m4 |   48 ---------------
> >  4 files changed, 96 insertions(+), 127 deletions(-)
> >  delete mode 100644 m4/compiler-flags.m4
> 
> > +
> > +        # List of warnings that are not relevant / wanted
> > +        dontwarn="$dontwarn -Wc++-compat"             # Don't care about C++ compiler compat
> > +        dontwarn="$dontwarn -Wtraditional"            # Don't care about ancient C standard compat
> > +        dontwarn="$dontwarn -Wtraditional-conversion" # Don't care about ancient C standard compat
> > +        dontwarn="$dontwarn -Wsystem-headers"         # Ignore warnings in /usr/include
> > +        dontwarn="$dontwarn -Wpadded"                 # Happy for compiler to add struct padding
> > +        dontwarn="$dontwarn -Wunreachable-code"       # GCC very confused with -O2
> > +        dontwarn="$dontwarn -Wconversion"             # Too many to deal with
> > +        dontwarn="$dontwarn -Wsign-conversion"        # Too many to deal with
> > +        dontwarn="$dontwarn -Wvla"                    # GNULIB gettext.h violates
> > +        dontwarn="$dontwarn -Wundef"                  # Many GNULIB violations
> > +        dontwarn="$dontwarn -Wcast-qual"              # Need to allow bad cast for execve()
> > +        dontwarn="$dontwarn -Wlong-long"              # We need to use long long in many places
> > +        dontwarn="$dontwarn -Wswitch-default"         # We allow manual list of all enum cases without default:
> > +        dontwarn="$dontwarn -Wswitch-enum"            # We allow optional default: instead of listing all enum values
> > +        dontwarn="$dontwarn -Wstrict-overflow"        # Not a problem since we don't use -fstrict-overflow
> > +        dontwarn="$dontwarn -Wunsafe-loop-optimizations" # Not a problem since we don't use -funsafe-loop-optimizations
> 
> Seems okay (but long lines - any way to break that into 80 columns?)
> 
> > +
> > +        # We might fundamentally need some of these disabled forever, but ideally
> > +        # we'd turn many of them on
> > +        dontwarn="$dontwarn -Wformat-nonliteral"
> 
> This one may need to always be disabled, thanks to virAsprintf (it would
> be nicer if we could disable for just one or two files, rather than
> globally).
> 
> > +        dontwarn="$dontwarn -Wfloat-equal"
> > +        dontwarn="$dontwarn -Wdeclaration-after-statement"
> 
> If gcc would do better, I'd love to guarantee C99 and take advantage of
> this (smaller scopes have maintenance benefits) - thus, I envision this
> one being permanent (float it up to the earlier set).
> 
> > +        dontwarn="$dontwarn -Wcast-qual"
> > +        dontwarn="$dontwarn -Wconversion"
> > +        dontwarn="$dontwarn -Wsign-conversion"
> > +        dontwarn="$dontwarn -Wold-style-definition"
> > +        dontwarn="$dontwarn -Wmissing-noreturn"
> > +        dontwarn="$dontwarn -Wpacked"
> > +        dontwarn="$dontwarn -Wunused-macros"
> > +        dontwarn="$dontwarn -Woverlength-strings"
> > +        dontwarn="$dontwarn -Wmissing-format-attribute"
> > +        dontwarn="$dontwarn -Wstack-protector"
> 
> Yes, I agree that the rest of these should be temporary, and are
> probably worth fixing.
> 
> > +
> > +        # Get all possible GCC warnings
> > +        gl_MANYWARN_ALL_GCC([maybewarn])
> > +
> > +        # Remove the ones we don't want, blacklisted earlier
> > +        gl_MANYWARN_COMPLEMENT([wantwarn], [$maybewarn], [$dontwarn])
> > +
> > +        # Check for $CC support of each warning
> > +        for w in $wantwarn; do
> > +          gl_WARN_ADD([$w])
> > +        done
> > +
> > +        # GNULIB uses '-W' which includes a bunch of stuff,
> > +        # kinda like -Wextra. Unfortunately, it means you
> 
> "kinda like"? Exactly like!  -W was the old spelling, -Wextra was the
> new one (added quite some time ago; something like gcc 3.4, off the top
> of my head).

Ah, I didn't realize it was the same.

> 
> > +        # can't simply use '-Wsign-compare' with gl_MANYWARN_COMPLEMENT
> > +        # So we have -W enabled, and then have to explicitly turn off
> > +        gl_WARN_ADD(-Wno-sign-compare)
> > +
> > +        # This should be < 256 really, but with PATH_MAX everywhere
> > +        # we have doom, even with 4096. In fact we have some functions
> > +        # with several PATH_MAX sized variables :-( We should kill off
> > +        # all PATH_MAX usage and then lower this limit
> > +        gl_WARN_ADD([-Wframe-larger-than=65700])
> > +        dnl gl_WARN_ADD([-Wframe-larger-than=4096])
> > +        dnl gl_WARN_ADD([-Wframe-larger-than=256])
> > +
> > +        # Extra special flags
> > +        gl_WARN_ADD([-Wp,-D_FORTIFY_SOURCE=2])
> > +        dnl Fedora only uses -fstack-protector, but doesn't seem to
> > +        dnl be great overhead in adding -fstack-protector-all instead
> > +        dnl gl_WARN_ADD([-fstack-protector])
> > +        gl_WARN_ADD([-fstack-protector-all])
> > +        gl_WARN_ADD([--param=ssp-buffer-size=4])
> > +        gl_WARN_ADD([-fexceptions])
> > +        gl_WARN_ADD([-fasynchronous-unwind-tables])
> > +        gl_WARN_ADD([-fdiagnostics-show-option])
> > +
> > +        if test "$enable_compile_warnings" = "error"
> > +        then
> > +          gl_WARN_ADD([-Werror])
> > +        fi
> 
> Looks like a good conversion.

I also added

  gl_WARN_ADD([-Wjump-misses-init])

because we loose that due to turning off  -Wc++-compat

Daniel
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