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

[David Gibson <david@gibson.dropbear.id.au>]

[-- Attachment #1: Type: text/plain, Size: 2209 bytes --]

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 <programmingkidx@gmail.com>

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.

> +{
> +    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.

If your environment does not provide strnlen(), you probably need your
own version of libfdt_env.h, which will need to define it.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]