Re: [PATCH v5 bpf-next 2/7] libbpf: cleanup after partial failure in bpf_object__pin

On 11/12, Martin Lau wrote:

On Mon, Nov 12, 2018 at 02:10:11PM -0800, Stanislav Fomichev wrote:

...

On 11/12, Martin Lau wrote:

...

On Fri, Nov 09, 2018 at 08:21:41AM -0800, Stanislav Fomichev wrote: [ ... ]

...

@@ -1918,23 +2160,20 @@ void *bpf_object__priv(struct bpf_object *obj) } static struct bpf_program * -__bpf_program__next(struct bpf_program *prev, struct bpf_object *obj) +__bpf_program__iter(struct bpf_program *p, struct bpf_object *obj, int i) {

• size_t idx;

• ssize_t idx;

if (!obj->programs) return NULL;

• /* First handler */
• if (prev == NULL)

• return &obj->programs[0];
  

• if (prev->obj != obj) {

• if (p->obj != obj) { pr_warning("error: program handler doesn't match object\n"); return NULL; }

• idx = (prev - obj->programs) + 1;
• if (idx >= obj->nr_programs)

• idx = (p - obj->programs) + i;
• if (idx >= obj->nr_programs || idx < 0) return NULL; return &obj->programs[idx];

} @@ -1944,8 +2183,29 @@ bpf_program__next(struct bpf_program *prev, struct bpf_object *obj) { struct bpf_program *prog = prev;

• if (prev == NULL)

• return obj->programs;
  

This patch breaks the behavior introduced in commit eac7d84519a3 ("tools: libbpf: don't return '.text' as a program for multi-function programs"): "Make bpf_program__next() skip over '.text' section if object file has pseudo calls. The '.text' section is hardly a program in that case, it's more of a storage for code of functions other than main."

For example, the userspace could have been doing: prog = bpf_program__next(NULL, obj); bpf_program__set_type(prog, BPF_PROG_TYPE_TRACEPOINT); bpf_object__load(obj);

For the bpf_prog.o that has pseudo calls, after this patch in bpf-next, the prog returned by bpf_program__next() could be in ".text" instead of the main bpf program. The next bpf_program__set_type() has no effect to the main program. The following bpf_object__load() will catch user in surprise with the main bpf prog in the wrong BPF_PROG_TYPE.

Will something like the following fix your concern? (plus, assuming the same for prev):

--- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -2216,8 +2216,11 @@ bpf_program__next(struct bpf_program *prev, struct bpf_object *obj) { struct bpf_program *prog = prev;

•   if (prev == NULL)
  

•           return obj->programs;
  

•   if (prev == NULL) {
  

•           prog = obj->programs;
  

•           if (!prog || !bpf_program__is_function_storage(prog, obj))
  

•                   return prog;
  

•   }
  

do { prog = __bpf_program__iter(prog, obj, 1);

Any suggestions for a better way to do it?

I think that would work. The bpf_program__prev() will need the same treatment though...

Here is my mostly untested fix to unblock my other dev works. It moves the very first NULL check back to __bpf_program__iter():

I like your version and it works with my simple flow dissector test :-) Thanks for spotting and fixing it!

From de1c89ae1768e756825a6874268b5b1686695c93 Mon Sep 17 00:00:00 2001 From: Martin KaFai Lau kafai@fb.com Date: Mon, 12 Nov 2018 14:52:39 -0800 Subject: [PATCH] bpf: libbpf: Fix bpf_program__next() API

This patch restores the behavior in commit eac7d84519a3 ("tools: libbpf: don't return '.text' as a program for multi-function programs"): such that bpf_program__next() does not return pseudo programs in ".text".

Fixes: 0c19a9fbc9cd ("libbpf: cleanup after partial failure in bpf_object__pin") Signed-off-by: Martin KaFai Lau kafai@fb.com

---

tools/lib/bpf/libbpf.c | 25 +++++++++++-------------- 1 file changed, 11 insertions(+), 14 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index e827542ffa3a..a01eb9584e52 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -2193,19 +2193,25 @@ void *bpf_object__priv(struct bpf_object *obj) } static struct bpf_program * -__bpf_program__iter(struct bpf_program *p, struct bpf_object *obj, int i) +__bpf_program__iter(struct bpf_program *p, struct bpf_object *obj, bool forward) {

• size_t nr_programs = obj->nr_programs; ssize_t idx;

• if (!obj->programs)

• if (!nr_programs) return NULL;

• if (!p)

• /* Iter from the beginning */
  

• return forward ? &obj->programs[0] :
  

• 	&obj->programs[nr_programs - 1];
  

• if (p->obj != obj) { pr_warning("error: program handler doesn't match object\n"); return NULL; }

• idx = (p - obj->programs) + i;

• idx = (p - obj->programs) + (forward ? 1 : -1); if (idx >= obj->nr_programs || idx < 0) return NULL; return &obj->programs[idx];

@@ -2216,11 +2222,8 @@ bpf_program__next(struct bpf_program *prev, struct bpf_object *obj) { struct bpf_program *prog = prev;

• if (prev == NULL)

• return obj->programs;
  

• do {

• prog = __bpf_program__iter(prog, obj, 1);
  

• prog = __bpf_program__iter(prog, obj, true);
  

  } while (prog && bpf_program__is_function_storage(prog, obj));

return prog; @@ -2231,14 +2234,8 @@ bpf_program__prev(struct bpf_program *next, struct bpf_object *obj) { struct bpf_program *prog = next;

• if (next == NULL) {

• if (!obj->nr_programs)
  

• 	return NULL;
  

• return obj->programs + obj->nr_programs - 1;
  

• }
• do {

• prog = __bpf_program__iter(prog, obj, -1);
  

• prog = __bpf_program__iter(prog, obj, false);
  

  } while (prog && bpf_program__is_function_storage(prog, obj));

return prog; -- 2.17.1

...

...

...

do {

• prog = __bpf_program__next(prog, obj);
  

• prog = __bpf_program__iter(prog, obj, 1);
  

• } while (prog && bpf_program__is_function_storage(prog, obj));
• return prog;

+}

+struct bpf_program * +bpf_program__prev(struct bpf_program *next, struct bpf_object *obj) +{

• struct bpf_program *prog = next;
• if (next == NULL) {

• if (!obj->nr_programs)
  

• 	return NULL;
  

• return obj->programs + obj->nr_programs - 1;
  

• }
• do {

• prog = __bpf_program__iter(prog, obj, -1);
  

  } while (prog && bpf_program__is_function_storage(prog, obj));

return prog;