netdev - Re: [PATCH 1/1] tools/lib/libbpf.c: fix string format to allow build on arm32

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Date:   Wed, 23 May 2018 08:49:47 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Daniel Borkmann <daniel@...earbox.net>,
        Sirio Balmelli <sirio@...d.ch>
CC:     <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/1] tools/lib/libbpf.c: fix string format to allow build
 on arm32

On Wed, May 23, 2018 at 12:41:14PM +0200, Daniel Borkmann wrote:
> [ +Martin ]
> 
> On 05/21/2018 08:59 AM, Sirio Balmelli wrote:
> > On arm32, 'cd tools/testing/selftests/bpf && make' fails with:
> > 
> > libbpf.c:80:10: error: format ‘%ld’ expects argument of type ‘long int’, but argument 4 has type ‘int64_t {aka long long int}’ [-Werror=format=]
> >    (func)("libbpf: " fmt, ##__VA_ARGS__); \
> >           ^
> > libbpf.c:83:30: note: in expansion of macro ‘__pr’
> >  #define pr_warning(fmt, ...) __pr(__pr_warning, fmt, ##__VA_ARGS__)
> >                               ^~~~
> > libbpf.c:1072:3: note: in expansion of macro ‘pr_warning’
> >    pr_warning("map:%s value_type:%s has BTF type_size:%ld != value_size:%u\n",
> > 
> > To fix, include 'inttypes.h' and change format directive to 'PRIi64'.
> > 
> > Signed-off-by: Sirio Balmelli <sirio@...d.ch>
> 
> Thanks for the fix! One minor comment below.
> 
> > ---
> >  tools/lib/bpf/libbpf.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index 3dbe217bf23e..e2cc8f10c188 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -48,6 +48,8 @@
> >  #include "bpf.h"
> >  #include "btf.h"
> >  
> > +#include <inttypes.h>   /* PRIi64 */
> > +
> >  #ifndef EM_BPF
> >  #define EM_BPF 247
> >  #endif
> > @@ -1042,7 +1044,7 @@ static int bpf_map_find_btf_info(struct bpf_map *map, const struct btf *btf)
> >  	}
> >  
> >  	if (def->key_size != key_size) {
> > -		pr_warning("map:%s key_type:%s has BTF type_size:%ld != key_size:%u\n",
> > +		pr_warning("map:%s key_type:%s has BTF type_size:%"PRIi64" != key_size:%u\n",
> >  			   map->name, name, key_size, def->key_size);
> >  		return -EINVAL;
> >  	}
> > @@ -1069,7 +1071,7 @@ static int bpf_map_find_btf_info(struct bpf_map *map, const struct btf *btf)
> >  	}
> >  
> >  	if (def->value_size != value_size) {
> > -		pr_warning("map:%s value_type:%s has BTF type_size:%ld != value_size:%u\n",
> > +		pr_warning("map:%s value_type:%s has BTF type_size:%"PRIi64" != value_size:%u\n",
> >  			   map->name, name, value_size, def->value_size);
> 
> I don't think we need the PRIi64 in here. Could you just change it to 'type_size:%u'
> and then cast the 'key_size' resp. 'value_size' to unsigned int? We know at this
> point that the type size value is positive anyway, so we only want to show the size
> mismatch so simple cast should suffice. Thanks!
Good point.  'unsigned int' is enough because the t->size (returned
by btf_type_size()) is a u32.

> 
> >  		return -EINVAL;
> >  	}
> > 
>