Re: [Qemu-devel] [PATCH] fdt_ro.c: implement strnlen

[Programmingkid]

> On Oct 18, 2017, at 9:31 PM, David Gibson <address@hidden> wrote:
> 
> On Wed, Oct 18, 2017 at 06:31:16PM -0400, John Arbuckle wrote:
>> Implement the strnlen() function if it isn't implemented.
>> 
>> Signed-off-by: John Arbuckle <address@hidden>
> 
> Nice idea, but this won't work.
> 
>> ---
>> libfdt/fdt_ro.c | 24 ++++++++++++++++++++++++
>> 1 file changed, 24 insertions(+)
>> 
>> diff --git a/libfdt/fdt_ro.c b/libfdt/fdt_ro.c
>> index 3d00d2e..a7986fb 100644
>> --- a/libfdt/fdt_ro.c
>> +++ b/libfdt/fdt_ro.c
>> @@ -55,6 +55,30 @@
>> 
>> #include "libfdt_internal.h"
>> 
>> +/* if the current environment does not define strnlen */
>> +#ifndef strnlen
> 
> This will only trigger if strnlen is defined as a macro.  The C
> library (or other environment) *might* do that, but there's no
> guarantee, whether or not it defines strnlen as a function.  With
> extra complications if the compiler has a strnlen builtin like gcc.

:(

>> +
>> +/* This eliminates the missing prototype warning */
>> +int strnlen(const char *string, int max_count);
>> +
>> +/*
>> + * strnlen: return the length of a string or max_count
>> + * which ever is shortest
>> + */
>> +
>> +int strnlen(const char *string, int max_count)
> 
> Also strnlen is supposed to take and return size_t, not int.

Will change this.

> 
>> +{
>> +    int count;
>> +    for(count = 0; count < max_count; count++) {
>> +        if (string[count] == '\0') {
>> +            break;
>> +        }
>> +    }
>> +    return count;
>> +}
>> +
>> +#endif /* strnlen */
>> +
>> static int _fdt_nodename_eq(const void *fdt, int offset,
>>                          const char *s, int len)
>> {
> 
> In any case, this sort of compatibility munging is the job of
> libfdt_env.h.  It's purpose is to provide all the external things that
> libfdt needs - there's not that many of them and strnlen() is one.
> The included libfdt_env.h is intended for POSIXy userspace
> environments, which should already include strnlen() in string.h.

QEMU supports Mac OS 10.5 and higher. The strnlen() function might have been 
added to Mac OS X in version 10.7. libfdt prevents QEMU from compiling on Mac 
OS X because of the missing strnlen() function. This issue needs to be 
resolved. If libfdt_env.h is where you want a fix located, would something like 
this be good:

#ifdef __APPLE__

#if (MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_7)
        size_t strnlen(const char *string, int max_count)
        {
                ... // pretend this is implemented
        }
#endif 

#endif