On 06 Oct 2022 06:43, Tsukasa OI wrote:
> Clang generates a warning if there is a function declaration/definition
> with zero arguments.  Such declarations/definitions without a prototype (an
> argument list) are deprecated forms of indefinite arguments
> ("-Wdeprecated-non-prototype").  On the default configuration, it causes a
> build failure (unless "--disable-werror" is specified).
> 
> include/getopt.h defines some getopt function definitions but one of them
> has a form "extern int getopt ();".  If this form is selected in
> include/getopt.h, Clang generates a warning and the build fails by default.
> 
> In really old environments, this getopt definition with no arguments is
> necessary (because the definition may change between environments).
> However, this definition is now a cause of problems on modern environments.
> 
> A good news is, this definition is not always selected (e.g. if used by
> binutils/*.c).  This is because configuration scripts of binutils, gas,
> gprof and ld tries to find known definition of getopt function is used and
> defines HAVE_DECL_GETOPT macro.  If this macro is defined when getopt.h is
> included, a good form of getopt is used and Clang won't generate warnings.
> 
> This commit adds a modified portion of ld/configure.ac to find the known
> getopt definition.  If we could find one (and we *will* in most modern
> environments), we don't need to rely on the deprecated definition.
> ---
>  sim/config.h.in  |  3 +++
>  sim/configure    | 32 ++++++++++++++++++++++++++++++++
>  sim/configure.ac | 10 ++++++++++

this logic belongs in m4/sim_ac_platform.m4, not configure.ac

should leave a comment above the code too indicating that this logic is
purely for local getopt.h usage, and is copied from other dirs (e.g. the
binutils files).
-mike