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

[Stefan Hajnoczi]

On Mon, Oct 23, 2017 at 11:13:13PM -0400, Programmingkid wrote:
> 
> > On Oct 23, 2017, at 12:09 PM, Stefan Hajnoczi <address@hidden> wrote:
> > 
> > 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 <address@hidden>
> >> ---
> >> 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
> 
> Sounds logical.
> 
> > 
> >> +/* 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).
> 
> If MAC_OS_X_VERSION_MAX_ALLOWED is equal to 1070 then this code would not be 
> executed. This branch would only be taken if MAC_OS_X_VERSION_MAX_ALLOWED is 
> less than 1070. So there would not be a 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
> 
> I think you are saying I should remove the "#ifdef __APPLE__" code and just 
> check to see if MAC_OS_X_VERSION_10_7 is defined. That might work on Mac OS 
> 10.6 and 10.5, but it would probably cause problems with non-Mac-OS 
> platforms. 

No, the ifndef is still "indented" and it would be like this:

#ifdef __APPLE_
...
# ifndef MAC_OS_X_VERSION_10_7