On 10/25/2016 08:00 PM, Chandrasekar Kannan via iovisor-dev wrote:
[...]
But when I try to run the sample from the linux source tree under release
(v4.8),
I get some strange errors.

"Error fetching program/map!
Failed to retrieve (e)BPF data!"

Details here : http://pastebin.com/raw/CTfq65ap

Any help appreciated...

Issue is that llc generates empty obj file with no program/map section in
it and tc loader fails to parse the ELF. Reason is that compilation fails
for some samples with clang since they unfortunately include kernel headers
and thus expect KBUILD_MODNAME defined due to dynamic debug enabled ... :/
I'll submit this band-aid ... since this is lingering for a while.

diff --git a/samples/bpf/parse_ldabs.c b/samples/bpf/parse_ldabs.c
index d175501..6db6b21 100644
--- a/samples/bpf/parse_ldabs.c
+++ b/samples/bpf/parse_ldabs.c
@@ -4,6 +4,7 @@
  * modify it under the terms of version 2 of the GNU General Public
  * License as published by the Free Software Foundation.
  */
+#define KBUILD_MODNAME "foo"
 #include <linux/ip.h>
 #include <linux/ipv6.h>
 #include <linux/in.h>
diff --git a/samples/bpf/parse_simple.c b/samples/bpf/parse_simple.c
index cf2511c..10af53d 100644
--- a/samples/bpf/parse_simple.c
+++ b/samples/bpf/parse_simple.c
@@ -4,6 +4,7 @@
  * modify it under the terms of version 2 of the GNU General Public
  * License as published by the Free Software Foundation.
  */
+#define KBUILD_MODNAME "foo"
 #include <linux/ip.h>
 #include <linux/ipv6.h>
 #include <linux/in.h>
diff --git a/samples/bpf/parse_varlen.c b/samples/bpf/parse_varlen.c
index edab34d..95c1632 100644
--- a/samples/bpf/parse_varlen.c
+++ b/samples/bpf/parse_varlen.c
@@ -4,6 +4,7 @@
  * modify it under the terms of version 2 of the GNU General Public
  * License as published by the Free Software Foundation.
  */
+#define KBUILD_MODNAME "foo"
 #include <linux/if_ether.h>
 #include <linux/ip.h>
 #include <linux/ipv6.h>
diff --git a/samples/bpf/tcbpf1_kern.c b/samples/bpf/tcbpf1_kern.c
index fa051b3..274c884 100644
--- a/samples/bpf/tcbpf1_kern.c
+++ b/samples/bpf/tcbpf1_kern.c
@@ -1,3 +1,4 @@
+#define KBUILD_MODNAME "foo"
 #include <uapi/linux/bpf.h>
 #include <uapi/linux/if_ether.h>
 #include <uapi/linux/if_packet.h>
diff --git a/samples/bpf/tcbpf2_kern.c b/samples/bpf/tcbpf2_kern.c
index 3303bb8..9c823a6 100644
--- a/samples/bpf/tcbpf2_kern.c
+++ b/samples/bpf/tcbpf2_kern.c
@@ -5,6 +5,7 @@
  * modify it under the terms of version 2 of the GNU General Public
  * License as published by the Free Software Foundation.
  */
+#define KBUILD_MODNAME "foo"
 #include <uapi/linux/bpf.h>
 #include <uapi/linux/if_ether.h>
 #include <uapi/linux/if_packet.h>
diff --git a/samples/bpf/test_cgrp2_tc_kern.c b/samples/bpf/test_cgrp2_tc_kern.c
index 10ff734..1547b36 100644
--- a/samples/bpf/test_cgrp2_tc_kern.c
+++ b/samples/bpf/test_cgrp2_tc_kern.c
@@ -4,6 +4,7 @@
  * modify it under the terms of version 2 of the GNU General Public
  * License as published by the Free Software Foundation.
  */
+#define KBUILD_MODNAME "foo"
 #include <uapi/linux/if_ether.h>
 #include <uapi/linux/in6.h>
 #include <uapi/linux/ipv6.h>
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