linux-kernel - Re: [PATCH bpf-next 4/5] samples/bpf: Refine printing symbol for sampleip

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Message-ID: <20180419052124.xzaz66vehd6pofnh@ast-mbp>
Date:   Wed, 18 Apr 2018 22:21:25 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 4/5] samples/bpf: Refine printing symbol for
 sampleip

On Thu, Apr 19, 2018 at 01:12:49PM +0800, Leo Yan wrote:
> On Wed, Apr 18, 2018 at 09:47:45PM -0700, Alexei Starovoitov wrote:
> > On Thu, Apr 19, 2018 at 09:34:05AM +0800, Leo Yan wrote:
> > > The code defines macro 'PAGE_OFFSET' and uses it to decide if the
> > > address is in kernel space or not.  But different architecture has
> > > different 'PAGE_OFFSET' so this program cannot be used for all
> > > platforms.
> > > 
> > > This commit changes to check returned pointer from ksym_search() to
> > > judge if the address falls into kernel space or not, and removes
> > > macro 'PAGE_OFFSET' as it isn't used anymore.  As result, this program
> > > has no architecture dependency.
> > > 
> > > Signed-off-by: Leo Yan <leo.yan@...aro.org>
> > > ---
> > >  samples/bpf/sampleip_user.c | 8 +++-----
> > >  1 file changed, 3 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/samples/bpf/sampleip_user.c b/samples/bpf/sampleip_user.c
> > > index 4ed690b..0eea1b3 100644
> > > --- a/samples/bpf/sampleip_user.c
> > > +++ b/samples/bpf/sampleip_user.c
> > > @@ -26,7 +26,6 @@
> > >  #define DEFAULT_FREQ	99
> > >  #define DEFAULT_SECS	5
> > >  #define MAX_IPS		8192
> > > -#define PAGE_OFFSET	0xffff880000000000
> > >  
> > >  static int nr_cpus;
> > >  
> > > @@ -107,14 +106,13 @@ static void print_ip_map(int fd)
> > >  	/* sort and print */
> > >  	qsort(counts, max, sizeof(struct ipcount), count_cmp);
> > >  	for (i = 0; i < max; i++) {
> > > -		if (counts[i].ip > PAGE_OFFSET) {
> > > -			sym = ksym_search(counts[i].ip);
> > 
> > yes. it is x64 specific, since it's a sample code,
> > but simply removing it is not a fix.
> > It makes this sampleip code behaving incorrectly.
> > To do such 'cleanup of ksym' please refactor it in the true generic way,
> > so these ksym* helpers can work on all archs and put this new
> > functionality into selftests.
> 
> Just want to check, are you suggesting to create a standalone
> testing for kallsyms (like a folder tools/testing/selftests/ksym) or
> do you mean to place the generic code into folder
> tools/testing/selftests/bpf/?

I think the minimal first step is to cleanup ksym bits into something
that bpf selftests can use and keep it as new .c in
tools/testing/selftests/bpf/
Later if it becomes useful for other tests in selftests it can be moved.

Thanks!