Re: memcmp and cross-compilation

[Jim Meyering]

Simon Josefsson <address@hidden> wrote:
>>>> MinGW apparently needs gnulib's memcmp module
>>>
>>> That was rather surprising to me, so I started investigating why that is
>>> the case.
>>
>> The reason was that Autoconf's AC_FUNC_MEMCMP uses AC_RUN_IFELSE with a
>> cross-compile default of no.  I prefer to assume memcmp exists on
>> cross-compile targets since I assume C89 or later in my projects.  That
>> is probably not the right choice for autoconf, but I think it is for

Hi Simon,

These days, I'd guess that the least common denominator cross-compiling
target environment is C89 -- and consistently more modern than the minimal
native environment, so Autoconf might need to review assumptions like that.
The trouble is that the penalty for making a mistake is incorrect operation,
while maintaining the status quo is merely degraded performance.

>> gnulib.  Thus it seems gnulib needs to extend autoconf's test somewhat?
>> I'll suggest something for review.
>
> The patch below works in the sense that, for cross-compilations only, it
> will assume that memcmp works when it is declared.  This works better
> for MinGW.
...
> Jim, what do you think?
...
>  AC_DEFUN([gl_FUNC_MEMCMP],
>  [
> +  if test $cross_compiling != no; then
> +    # AC_FUNC_MEMCMP as of 2.62 defaults to 'no' when cross compiling.
> +    # We default to yes if memcmp appears to exist, which works
> +    # better for MinGW.
> +    AC_CACHE_CHECK([whether cross-compiling target has memcmp],
> +                   [ac_cv_func_memcmp_working],
> +                   [AC_LINK_IFELSE([
> +                     AC_LANG_PROGRAM([[#include <string.h>
> +                             ]], [[int ret = memcmp ("foo", "bar", 0)]])],

That looks fine.
However, please add the conventional semicolon:

                                ]], [[int ret = memcmp ("foo", "bar", 0);]])],

I know it's not officially needed, since AC_LANG_PROGRAM
provides one, but I had to look to confirm that.
You're welcome to commit the result.
Thanks!