Subject: Re: [PATCH iproute2] json_print: fix print_uint hidden type promotion

From: Stephen Hemminger <[email-masked]>
Date: Thu, 29 Mar 2018 14:02:37 -0700

On Thu, 29 Mar 2018 20:22:20 +0100
Kevin Darbyshire-Bryant <[email-masked]> wrote:

> print_int used 'int' type internally, whereas print_uint used 'uint64_t'
> 
> These helper functions eventually call vfprintf(fp, fmt, args) which is
> a variable argument list function and is dependent upon 'fmt' containing
> correct information about the length of the passed arguments.
> 
> Unfortunately print_int v print_uint offered no clue to the programmer
> that internally passed ints to print_uint were being promoted to 64bits,
> thus the format passed in 'fmt' string vs the actual passed integer
> could be different lengths.  This is even more interesting on big endian
> architectures where 'vfprintf' would be looking in the middle of an
> int64 type.
> 
> print_u/int now stick with native int size.
> 
> Signed-off-by: Kevin Darbyshire-Bryant <[email-masked]>
> ---
>  include/json_print.h | 2 +-
>  lib/json_print.c     | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/json_print.h b/include/json_print.h
> index 2ca7830a..45bc653d 100644
> --- a/include/json_print.h
> +++ b/include/json_print.h
> @@ -56,10 +56,10 @@ void close_json_array(enum output_type type, const char *delim);
>  		print_color_##type_name(t, COLOR_NONE, key, fmt, value);	\
>  	}
>  _PRINT_FUNC(int, int);
> +_PRINT_FUNC(uint, unsigned int);
>  _PRINT_FUNC(bool, bool);
>  _PRINT_FUNC(null, const char*);
>  _PRINT_FUNC(string, const char*);
> -_PRINT_FUNC(uint, uint64_t);
>  _PRINT_FUNC(hu, unsigned short);
>  _PRINT_FUNC(hex, unsigned int);
>  _PRINT_FUNC(0xhex, unsigned int);
> diff --git a/lib/json_print.c b/lib/json_print.c
> index 6518ba98..8d54d1d4 100644
> --- a/lib/json_print.c
> +++ b/lib/json_print.c
> @@ -117,8 +117,8 @@ void close_json_array(enum output_type type, const char *str)
>  		}							\
>  	}
>  _PRINT_FUNC(int, int);
> +_PRINT_FUNC(uint, unsigned int);
>  _PRINT_FUNC(hu, unsigned short);
> -_PRINT_FUNC(uint, uint64_t);
>  _PRINT_FUNC(lluint, unsigned long long int);
>  _PRINT_FUNC(float, double);
>  #undef _PRINT_FUNC

I am concerned that this will break output of 64 bit statistics on 32 bit hosts.