Re: [Qemu-devel] [libfdt][PATCH v3] implement strnlen for systems that need it

[Stefan Hajnoczi <stefanha-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Sun, Oct 22, 2017 at 10:50:16PM -0400, John Arbuckle wrote:
> Prior the Mac OS 10.7, the function strnlen() was not available. This patch
> implements strnlen() on Mac OS X versions that are below 10.7.
> 
> Signed-off-by: John Arbuckle <programmingkidx-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> ---
> v3 changes:
> - Replaced loop with memchr()
> 
> v2 changes:
> - Simplified the code to make it static inline'ed
> - Changed the type of count to size_t
> 
>  libfdt/libfdt_env.h | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/libfdt/libfdt_env.h b/libfdt/libfdt_env.h
> index 952056c..d43b66b 100644
> --- a/libfdt/libfdt_env.h
> +++ b/libfdt/libfdt_env.h
> @@ -109,4 +109,28 @@ static inline fdt64_t cpu_to_fdt64(uint64_t x)
>  #undef CPU_TO_FDT16
>  #undef EXTRACT_BYTE
>  
> +#ifdef __APPLE__
> +#include <AvailabilityMacros.h>
> +
> +#define MAC_OS_X_VERSION_10_7 1070

Apple has already defined MAC_OS_X_VERSION_10_7 here:
https://opensource.apple.com/source/xnu/xnu-1699.24.8/EXTERNAL_HEADERS/AvailabilityMacros.h

To avoid a compiler warning, please use:

#ifndef MAC_OS_X_VERSION_10_7
#define MAC_OS_X_VERSION_10_7 1070
#endif

> +/* strnlen() is not available on Mac OS < 10.7 */
> +# if (MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_7)

Does this cover the case where MAC_OS_X_VERSION_MAX_ALLOWED is set to
<1070 on a 10.7+ build machine?  It's possible that the <string.h>
header would define strnlen() and your code redefines the function
(compiler error).

It would be best to check how <string.h>, <Availability.h>, and
<AvailabilityMacros.h> work to make sure that all cases are handled.  I
don't have access to a Mac right now, sorry.

Perhaps this approach works better:

# ifndef MAC_OS_X_VERSION_10_7