Re: [PATCH 5/5] bpf: Allow to resolve bpf trampoline in unwind

[Björn Töpel <bjorn.topel@xxxxxxxxx>]

On 2020-02-03 20:58, Jiri Olsa wrote:
[...]
> > > ...and FWIW, it would be nice with bpf_dispatcher_<...> entries in kallsyms
> >
> > ok so it'd be 'bpf_dispatcher_<name>'
>
> hi,
> so the only dispatcher is currently defined as:
>    DEFINE_BPF_DISPATCHER(bpf_dispatcher_xdp)
>
> with the bpf_dispatcher_<name> logic it shows in kallsyms as:
>    ffffffffa0450000 t bpf_dispatcher_bpf_dispatcher_xdp    [bpf]

Ick! :-P


> to fix that, would you guys preffer having:
>    DEFINE_BPF_DISPATCHER(xdp)
>
> or using the full dispatcher name as kallsyms name?
> which would require some discipline for future dispatcher names ;-)

I'd prefer the latter, i.e. name "xdp" is shown as bpf_dispatcher_xdp in 
kallsyms.

...and if this route is taken, the macros can be changed, so that the 
trampoline functions are prefixed with "bpf_dispatcher_". Something like 
this (and also a small '_' cleanup):


diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 8e9ad3943cd9..15c5f351f837 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -512,7 +512,7 @@ struct bpf_dispatcher {
 	u32 image_off;
 };

-static __always_inline unsigned int bpf_dispatcher_nopfunc(
+static __always_inline unsigned int bpf_dispatcher_nop_func(
 	const void *ctx,
 	const struct bpf_insn *insnsi,
 	unsigned int (*bpf_func)(const void *,
@@ -527,7 +527,7 @@ int bpf_trampoline_unlink_prog(struct bpf_prog *prog);
 void bpf_trampoline_put(struct bpf_trampoline *tr);
 #define BPF_DISPATCHER_INIT(name) {			\
 	.mutex = __MUTEX_INITIALIZER(name.mutex),	\
-	.func = &name##func,				\
+	.func = &name##_func,				\
 	.progs = {},					\
 	.num_progs = 0,					\
 	.image = NULL,					\
@@ -535,7 +535,7 @@ void bpf_trampoline_put(struct bpf_trampoline *tr);
 }

 #define DEFINE_BPF_DISPATCHER(name)					\
-	noinline unsigned int name##func(				\
+	noinline unsigned int bpf_dispatcher_##name##_func(		\
 		const void *ctx,					\
 		const struct bpf_insn *insnsi,				\
 		unsigned int (*bpf_func)(const void *,			\
@@ -543,17 +543,18 @@ void bpf_trampoline_put(struct bpf_trampoline *tr);
 	{								\
 		return bpf_func(ctx, insnsi);				\
 	}								\
-	EXPORT_SYMBOL(name##func);			\
-	struct bpf_dispatcher name = BPF_DISPATCHER_INIT(name);
+	EXPORT_SYMBOL(bpf_dispatcher_##name##_func);			\
+	struct bpf_dispatcher bpf_dispatcher_##name =			\
+		BPF_DISPATCHER_INIT(bpf_dispatcher_##name);
 #define DECLARE_BPF_DISPATCHER(name)					\
-	unsigned int name##func(					\
+	unsigned int bpf_dispatcher_##name##_func(			\
 		const void *ctx,					\
 		const struct bpf_insn *insnsi,				\
 		unsigned int (*bpf_func)(const void *,			\
 					 const struct bpf_insn *));	\
-	extern struct bpf_dispatcher name;
-#define BPF_DISPATCHER_FUNC(name) name##func
-#define BPF_DISPATCHER_PTR(name) (&name)
+	extern struct bpf_dispatcher bpf_dispatcher_##name;
+#define BPF_DISPATCHER_FUNC(name) bpf_dispatcher_##name##_func
+#define BPF_DISPATCHER_PTR(name) (&bpf_dispatcher_##name)
 void bpf_dispatcher_change_prog(struct bpf_dispatcher *d, struct 
bpf_prog *from,
 				struct bpf_prog *to);
 struct bpf_image {
@@ -579,7 +580,7 @@ static inline int bpf_trampoline_unlink_prog(struct 
bpf_prog *prog)
 static inline void bpf_trampoline_put(struct bpf_trampoline *tr) {}
 #define DEFINE_BPF_DISPATCHER(name)
 #define DECLARE_BPF_DISPATCHER(name)
-#define BPF_DISPATCHER_FUNC(name) bpf_dispatcher_nopfunc
+#define BPF_DISPATCHER_FUNC(name) bpf_dispatcher_nop_func
 #define BPF_DISPATCHER_PTR(name) NULL
 static inline void bpf_dispatcher_change_prog(struct bpf_dispatcher *d,
 					      struct bpf_prog *from,
diff --git a/include/linux/filter.h b/include/linux/filter.h
index f349e2c0884c..eafe72644282 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -577,7 +577,7 @@ DECLARE_STATIC_KEY_FALSE(bpf_stats_enabled_key);
 	ret; })

 #define BPF_PROG_RUN(prog, ctx) __BPF_PROG_RUN(prog, ctx,		\
-					       bpf_dispatcher_nopfunc)
+					       bpf_dispatcher_nop_func)

 #define BPF_SKB_CB_LEN QDISC_CB_PRIV_LEN

@@ -701,7 +701,7 @@ static inline u32 bpf_prog_run_clear_cb(const struct 
bpf_prog *prog,
 	return res;
 }

-DECLARE_BPF_DISPATCHER(bpf_dispatcher_xdp)
+DECLARE_BPF_DISPATCHER(xdp)

 static __always_inline u32 bpf_prog_run_xdp(const struct bpf_prog *prog,
 					    struct xdp_buff *xdp)
@@ -712,8 +712,7 @@ static __always_inline u32 bpf_prog_run_xdp(const 
struct bpf_prog *prog,
 	 * already takes rcu_read_lock() when fetching the program, so
 	 * it's not necessary here anymore.
 	 */
-	return __BPF_PROG_RUN(prog, xdp,
-			      BPF_DISPATCHER_FUNC(bpf_dispatcher_xdp));
+	return __BPF_PROG_RUN(prog, xdp, BPF_DISPATCHER_FUNC(xdp));
 }

 void bpf_prog_change_xdp(struct bpf_prog *prev_prog, struct bpf_prog 
*prog);
diff --git a/net/core/filter.c b/net/core/filter.c
index 792e3744b915..5db435141e16 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -8835,10 +8835,9 @@ const struct bpf_prog_ops sk_reuseport_prog_ops = {
 };
 #endif /* CONFIG_INET */

-DEFINE_BPF_DISPATCHER(bpf_dispatcher_xdp)
+DEFINE_BPF_DISPATCHER(xdp)

 void bpf_prog_change_xdp(struct bpf_prog *prev_prog, struct bpf_prog 
*prog)
 {
-	bpf_dispatcher_change_prog(BPF_DISPATCHER_PTR(bpf_dispatcher_xdp),
-				   prev_prog, prog);
+	bpf_dispatcher_change_prog(BPF_DISPATCHER_PTR(xdp), prev_prog, prog);
 }