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

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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():

>From de1c89ae1768e756825a6874268b5b1686695c93 Mon Sep 17 00:00:00 2001
From: Martin KaFai Lau <kafai@xxxxxx>
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@xxxxxx>
---
 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;




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