Re: [RFC PATCH v3 12/37] bpf tools: Collect version and license from ELF sections

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Mon, May 18, 2015 at 11:27:17AM -0700, Alexei Starovoitov escreveu:
> On 5/17/15 3:56 AM, Wang Nan wrote:
> >Expand bpf_obj_elf_collect() to collect license and kernel version
> >information in eBPF object file. eBPF object file should have a section
> >named 'license', which contains a string. It should also have a section
> >named 'version', contains a u32 LINUX_VERSION_CODE.
> >
> >bpf_obj_validate() is introduced to validate object file after loaded.
> >Currently it only check existance of 'version' section.
> >
> >Signed-off-by: Wang Nan <wangnan0@huawei.com>
> ...
> >+#ifdef min
> >+# undef min
> >+#endif
> >+#define min(x, y) ({				\
> >+	typeof(x) _min1 = (x);			\
> >+	typeof(y) _min2 = (y);			\
> >+	(void) (&_min1 == &_min2);		\
> >+	_min1 < _min2 ? _min1 : _min2; })
> >+
> 
> copy-paste from lib traceevent?
> there is another container_of copy-paste later in the patches.
> please use something like tools/lib/bpf/utils.h file for such
> things, so we can consolidate and share this code later.

Better, ask what the kernel does, find out where it does and replicate
that in tools/include/, i.e. a min function?!? This looks like useful
stuff! ;-)

So, the kernel has this one, in include/linux/kernel.h:

/*
 * min()/max()/clamp() macros that also do
 * strict type-checking.. See the
 * "unnecessary" pointer comparison.
 */
#define min(x, y) ({                            \
        typeof(x) _min1 = (x);                  \
        typeof(y) _min2 = (y);                  \
        (void) (&_min1 == &_min2);              \
        _min1 < _min2 ? _min1 : _min2; })

Looks a lot like that one above, no? :-)

So, lets take a look at: tools/include/linux/kernel.h... bummer, that
one wasn't yet moved from tools/perf/util/include/linux/kernel.h there.
Will do, and then it has this:

#ifndef min
#define min(x, y) ({                            \
        typeof(x) _min1 = (x);                  \
        typeof(y) _min2 = (y);                  \
        (void) (&_min1 == &_min2);              \
        _min1 < _min2 ? _min1 : _min2; })
#endif

We should minimize this mess :-)

- Arnaldo