On Mar 28, 2013, at 5:37 AM, Michael Richardson <m...@sandelman.ca> wrote:
>
> While I'll bet that 95% of *nix systems that compile tcpdump regularly
> are using gcc, I know that there remain other compilers in use.
...at least some of which may support -W options, and at least one of which
(clang) supports most if not all of the same -W options that GCC does.
> If one wants to add -W options to the standard build, I'm wondering what
> the right autoconf magic is to enable such a thing.
Wireshark's configure script checks whether the GCC shell variable is "yes" or
the CC shell variable is "clang" and, if true, sets a flag saying "this
compiler supports -W options".
It then has a macro that takes, as arguments,
a list of one or more flags to add;
an optional indication of whether the flags are for C, C++, or both;
an optional program to compile with the flag and with -Werror - if the
compile fails, the option is not added (this handles some flags that issue
incorrect or non-useful warnings with some compiler versions);
if the third argument is supplied, a fourth argument which is a message
describing what the test program is checking
and, if the compiler supports -W options, doesn't fail if you pass it the -W
option in question when compiling a trivial program (this tests whether the
option is supported at all), and, if the test program is supplied, it compiles
OK, it adds the flags to CFLAGS, CXXFLAGS, or both. (If the compiler is clang,
you also have to pass -Werror=unknown-warning-option, so the compiler doesn't
just print out a warning message and compile anyway; that way, we don't include
a pile of unsupported -W flags and get a pile of warnings for every
compilation.)
There's no C++ code in libpcap or tcpdump, so the second argument isn't
necessary.
The third and fourth arguments are used to:
avoid using -Wshadow if, when set, the compiler bogusly complains about
variables in function and function pointer declarations shadowing other
variables (which some versions of GCC do);
avoid using -Wlogical-op if strchr() is given a constant string;
so unless we plan to use those -W flags, we don't need them - no other tricky
-W flags were found.
> fxlb suggested:
> "-Wunused -Wunused-parameter"
>
> --
> ] Never tell me the odds! | ipv6 mesh networks
> [
> ] Michael Richardson, Sandelman Software Works | network architect
> [
> ] m...@sandelman.ca http://www.sandelman.ca/ | ruby on rails
> [
>
>
>
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