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Date: Sun, 26 Jul 2020 14:24:50 +0200
From: Jiri Olsa <jolsa@...hat.com>
To: Eelco Chaudron <echaudro@...hat.com>
Cc: Yonghong Song <yhs@...com>, bpf@...r.kernel.org,
netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
kafai@...com, songliubraving@...com, andriin@...com,
toke@...hat.com
Subject: Re: fentry/fexit attach to EXT type XDP program does not work
On Tue, Jun 09, 2020 at 10:52:34AM +0200, Eelco Chaudron wrote:
SNIP
> > > libbpf: failed to load object 'test_xdp_bpf2bpf'
> > > libbpf: failed to load BPF skeleton 'test_xdp_bpf2bpf': -4007
> > > test_xdp_fentry_ext:FAIL:__load ftrace skeleton failed
> > > #91 xdp_fentry_ext:FAIL
> > > Summary: 0/0 PASSED, 0 SKIPPED, 1 FAILED
> > >
> > > Any idea what could be the case here? The same fentry/fexit attach
> > > code works fine in the xdp_bpf2bpf.c tests case.
>
> <SNIP>
> >
> > I think this is not supported now. That is, you cannot attach a fentry
> > trace
> > to the EXT program. The current implementation for fentry program simply
> > trying to find and match the signature of freplace program which by
> > default
> > is a pointer to void.
> >
> > It is doable in that in kernel we could recognize to-be-attached program
> > is
> > a freplace and further trace down to find the real signature. The
> > related
> > kernel function is btf_get_prog_ctx_type(). You can try to implement by
> > yourself
> > or I can have a patch for this once bpf-next opens.
>
> I’m not familiar with this area of the code, so if you could prepare a patch
> that would nice.
> You can also send it to me before bpf-next opens and I can verify it, and
> clean up the self-test so it can be included as well.
>
hi,
it seems that you cannot exten fentry/fexit programs,
but it's possible to attach fentry/fexit to ext program.
/* Program extensions can extend all program types
* except fentry/fexit. The reason is the following.
* The fentry/fexit programs are used for performance
* analysis, stats and can be attached to any program
* type except themselves. When extension program is
* replacing XDP function it is necessary to allow
* performance analysis of all functions. Both original
* XDP program and its program extension. Hence
* attaching fentry/fexit to BPF_PROG_TYPE_EXT is
* allowed. If extending of fentry/fexit was allowed it
* would be possible to create long call chain
* fentry->extension->fentry->extension beyond
* reasonable stack size. Hence extending fentry is not
* allowed.
*/
I changed fexit_bpf2bpf.c test just to do a quick check
and it seems to work:
# echo > /sys/kernel/debug/tracing/trace
# ./test_progs -t fexit_bpf2bpf
#25 fexit_bpf2bpf:OK
Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED
# cat /sys/kernel/debug/tracing/trace | tail -2
<...>-75365 [012] d... 313932.416780: bpf_trace_printk: ENTRY val 123
<...>-75365 [012] d... 313932.416784: bpf_trace_printk: EXIT val 123, ret 1
jirka
---
diff --git a/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c b/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
index a895bfed55db..4b6c26ac2362 100644
--- a/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
+++ b/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
@@ -17,6 +17,7 @@ static void test_fexit_bpf2bpf_common(const char *obj_file,
struct bpf_map *data_map;
const int zero = 0;
u64 *result = NULL;
+ int ext_fd;
err = bpf_prog_load(target_obj_file, BPF_PROG_TYPE_UNSPEC,
&pkt_obj, &pkt_fd);
@@ -51,11 +52,50 @@ static void test_fexit_bpf2bpf_common(const char *obj_file,
link[i] = bpf_program__attach_trace(prog[i]);
if (CHECK(IS_ERR(link[i]), "attach_trace", "failed to link\n"))
goto close_prog;
+
+ if (!strcmp(prog_name[i], "freplace/get_constant"))
+ ext_fd = bpf_program__fd(prog[i]);
}
if (!run_prog)
goto close_prog;
+{
+ struct bpf_object *obj_trace = NULL;
+ struct bpf_program *prog_trace = NULL;
+ struct bpf_link *link_trace = NULL;
+
+ DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts_trace,
+ .attach_prog_fd = ext_fd,
+ );
+
+ obj_trace = bpf_object__open_file("trace_ext.o", &opts_trace);
+ if (CHECK(IS_ERR_OR_NULL(obj_trace), "obj_open",
+ "failed to open %s: %ld\n", obj_file,
+ PTR_ERR(obj_trace)))
+ goto close_prog;
+
+ err = bpf_object__load(obj_trace);
+ if (CHECK(err, "obj_load", "err %d\n", err))
+ goto close_prog;
+
+ prog_trace = bpf_object__find_program_by_title(obj_trace, "fexit/new_get_constant");
+ if (CHECK(!prog_trace, "find_prog", "prog %s not found\n", "fexit/new_get_constant"))
+ goto close_prog;
+
+ link_trace = bpf_program__attach_trace(prog_trace);
+ if (CHECK(IS_ERR(link_trace), "attach_trace", "failed to link\n"))
+ goto close_prog;
+
+ prog_trace = bpf_object__find_program_by_title(obj_trace, "fentry/new_get_constant");
+ if (CHECK(!prog_trace, "find_prog", "prog %s not found\n", "fentry/new_get_constant"))
+ goto close_prog;
+
+ link_trace = bpf_program__attach_trace(prog_trace);
+ if (CHECK(IS_ERR(link_trace), "attach_trace", "failed to link\n"))
+ goto close_prog;
+}
+
data_map = bpf_object__find_map_by_name(obj, "fexit_bp.bss");
if (CHECK(!data_map, "find_data_map", "data map not found\n"))
goto close_prog;
@@ -88,6 +128,7 @@ static void test_fexit_bpf2bpf_common(const char *obj_file,
free(result);
}
+#if 0
static void test_target_no_callees(void)
{
const char *prog_name[] = {
@@ -112,6 +153,7 @@ static void test_target_yes_callees(void)
ARRAY_SIZE(prog_name),
prog_name, true);
}
+#endif
static void test_func_replace(void)
{
@@ -130,6 +172,7 @@ static void test_func_replace(void)
prog_name, true);
}
+#if 0
static void test_func_replace_verify(void)
{
const char *prog_name[] = {
@@ -140,11 +183,9 @@ static void test_func_replace_verify(void)
ARRAY_SIZE(prog_name),
prog_name, false);
}
+#endif
void test_fexit_bpf2bpf(void)
{
- test_target_no_callees();
- test_target_yes_callees();
test_func_replace();
- test_func_replace_verify();
}
diff --git a/tools/testing/selftests/bpf/progs/trace_ext.c b/tools/testing/selftests/bpf/progs/trace_ext.c
new file mode 100644
index 000000000000..c7eaf30bf5ba
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/trace_ext.c
@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include <stddef.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_endian.h>
+#include <bpf/bpf_tracing.h>
+
+
+SEC("fentry/new_get_constant")
+int BPF_PROG(test_fentry_new_get_constant, long val)
+{
+ bpf_printk("ENTRY val %ld", val);
+ return 0;
+}
+
+SEC("fexit/new_get_constant")
+int BPF_PROG(test_fexit_new_get_constant, long val, int ret)
+{
+ bpf_printk("EXIT val %ld, ret %d", val, ret);
+ return 0;
+}
+
+char _license[] SEC("license") = "GPL";
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