Re: [PATCH] bpftool: Add missing libgen.h for basename()

[Jiri Olsa <olsajiri@gmail.com>]

On Thu, Jan 04, 2024 at 12:04:17AM -0300, Arnaldo Carvalho de Melo wrote:
> The header with the prototype for basename() is missing in the gen.c
> file, which breaks the build in distros where that header doesn't get
> include by some of the other includes present in gen.c, by luck, fix it.
> 
> Noticed when build perf on the Alpine Linux edge.
> 
> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> 
> ---
> 
> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> index ee3ce2b8000d75d2..0e50722588b48fa0 100644
> --- a/tools/bpf/bpftool/gen.c
> +++ b/tools/bpf/bpftool/gen.c
> @@ -7,6 +7,7 @@
>  #include <ctype.h>
>  #include <errno.h>
>  #include <fcntl.h>
> +#include <libgen.h>
>  #include <linux/err.h>
>  #include <stdbool.h>
>  #include <stdio.h>

hi,
this gives me compile warning on fedora:

	gen.c: In function ‘get_obj_name’:
	gen.c:61:32: warning: passing argument 1 of ‘__xpg_basename’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
	   61 |         strncpy(name, basename(file), MAX_OBJ_NAME_LEN - 1);
	      |                                ^~~~
	In file included from gen.c:10:
	/usr/include/libgen.h:34:36: note: expected ‘char *’ but argument is of type ‘const char *’
	   34 | extern char *__xpg_basename (char *__path) __THROW;
	      |                              ~~~~~~^~~~~~


looks like there are 2 versions of basename (man 3 basename):

	VERSIONS
	       There are two different versions of basename() - the POSIX version described above, and the GNU version, which one gets after

		       #define _GNU_SOURCE         /* See feature_test_macros(7) */
		       #include <string.h>

	       The  GNU  version  never  modifies its argument, and returns the empty string when path has a trailing slash, and in particular also when it is "/".
	       There is no GNU version of dirname().

	       With glibc, one gets the POSIX version of basename() when <libgen.h> is included, and the GNU version otherwise.


I think we want to keep the GNU version declaration, but not sure how
to fix the bpftool on Alpine Linux edge, what's the exact build error?

jirka