[PATCHv3 bpf-next 0/3] perf tools: Fix prologue generation

[PATCHv3 bpf-next 0/3] perf tools: Fix prologue generation

[Jiri Olsa]

hi,
sending change we discussed some time ago [1] to get rid of
some deprecated functions we use in perf prologue code.

Despite the gloomy discussion I think the final code does
not look that bad ;-)

This patchset removes following libbpf functions from perf:
  bpf_program__set_prep
  bpf_program__nth_fd
  struct bpf_prog_prep_result

v3 changes:
  - removed R0/R1 zero init in libbpf_prog_prepare_load_fn,
    because it's not needed [Andrii]
  - rebased/post on top of bpf-next/master which now has
    all the needed perf/core changes

v2 changes:
  - use fallback section prog handler, so we don't need to
    use section prefix [Andrii]
  - realloc prog->insns array in bpf_program__set_insns [Andrii]
  - squash patch 1 from previous version with
    bpf_program__set_insns change [Daniel]
  - patch 3 already merged [Arnaldo]
  - added more comments

  meanwhile.. perf/core and bpf-next diverged, so:
    - libbpf bpf_program__set_insns change is based on bpf-next/master
    - perf changes do not apply on bpf-next/master so they are based on
      perf/core ... however they can be merged only after we release
      libbpf 0.8.0 with bpf_program__set_insns change, so we don't break
      the dynamic linking
      I'm sending perf changes now just for review, I'll resend them
      once libbpf 0.8.0 is released

thanks,
jirka


[1] https://lore.kernel.org/bpf/CAEf4BzaiBO3_617kkXZdYJ8hS8YF--ZLgapNbgeeEJ-pY0H88g@mail.gmail.com/
---
Jiri Olsa (2):
      perf tools: Register fallback libbpf section handler
      perf tools: Rework prologue generation code

 tools/perf/util/bpf-loader.c | 173 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 155 insertions(+), 18 deletions(-)

[PATCHv3 bpf-next 1/2] perf tools: Register fallback libbpf section handler

[Jiri Olsa]

Perf is using section name to declare special kprobe arguments,
which no longer works with current libbpf, that either requires
certain form of the section name or allows to register custom
handler.

Adding perf support to register 'fallback' section handler to take
care of perf kprobe programs. The fallback means that it handles
any section definition besides the ones that libbpf handles.

The handler serves two purposes:
  - allows perf programs to have special arguments in section name
  - allows perf to use pre-load callback where we can attach init
    code (zeroing all argument registers) to each perf program

The second is essential part of new prologue generation code,
that's coming in following patch.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/perf/util/bpf-loader.c | 45 ++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
index f8ad581ea247..e7992a0eb477 100644
--- a/tools/perf/util/bpf-loader.c
+++ b/tools/perf/util/bpf-loader.c
@@ -86,6 +86,7 @@ bpf_perf_object__next(struct bpf_perf_object *prev)
 	     (perf_obj) = (tmp), (tmp) = bpf_perf_object__next(tmp))
 
 static bool libbpf_initialized;
+static int libbpf_sec_handler;
 
 static int bpf_perf_object__add(struct bpf_object *obj)
 {
@@ -99,12 +100,56 @@ static int bpf_perf_object__add(struct bpf_object *obj)
 	return perf_obj ? 0 : -ENOMEM;
 }
 
+static struct bpf_insn prologue_init_insn[] = {
+	BPF_MOV64_IMM(BPF_REG_2, 0),
+	BPF_MOV64_IMM(BPF_REG_3, 0),
+	BPF_MOV64_IMM(BPF_REG_4, 0),
+	BPF_MOV64_IMM(BPF_REG_5, 0),
+};
+
+static int libbpf_prog_prepare_load_fn(struct bpf_program *prog,
+				       struct bpf_prog_load_opts *opts __maybe_unused,
+				       long cookie __maybe_unused)
+{
+	size_t init_size_cnt = ARRAY_SIZE(prologue_init_insn);
+	size_t orig_insn_cnt, insn_cnt, init_size, orig_size;
+	const struct bpf_insn *orig_insn;
+	struct bpf_insn *insn;
+
+	/* prepend initialization code to program instructions */
+	orig_insn = bpf_program__insns(prog);
+	orig_insn_cnt = bpf_program__insn_cnt(prog);
+	init_size = init_size_cnt * sizeof(*insn);
+	orig_size = orig_insn_cnt * sizeof(*insn);
+
+	insn_cnt = orig_insn_cnt + init_size_cnt;
+	insn = malloc(insn_cnt * sizeof(*insn));
+	if (!insn)
+		return -ENOMEM;
+
+	memcpy(insn, prologue_init_insn, init_size);
+	memcpy((char *) insn + init_size, orig_insn, orig_size);
+	bpf_program__set_insns(prog, insn, insn_cnt);
+	return 0;
+}
+
 static int libbpf_init(void)
 {
+	LIBBPF_OPTS(libbpf_prog_handler_opts, handler_opts,
+		.prog_prepare_load_fn = libbpf_prog_prepare_load_fn,
+	);
+
 	if (libbpf_initialized)
 		return 0;
 
 	libbpf_set_print(libbpf_perf_print);
+	libbpf_sec_handler = libbpf_register_prog_handler(NULL, BPF_PROG_TYPE_KPROBE,
+							  0, &handler_opts);
+	if (libbpf_sec_handler < 0) {
+		pr_debug("bpf: failed to register libbpf section handler: %d\n",
+			 libbpf_sec_handler);
+		return -BPF_LOADER_ERRNO__INTERNAL;
+	}
 	libbpf_initialized = true;
 	return 0;
 }
-- 
2.35.3

[PATCHv3 bpf-next 2/2] perf tools: Rework prologue generation code

[Jiri Olsa]

Some functions we use for bpf prologue generation are going to be
deprecated. This change reworks current code not to use them.

We need to replace following functions/struct:
   bpf_program__set_prep
   bpf_program__nth_fd
   struct bpf_prog_prep_result

Currently we use bpf_program__set_prep to hook perf callback before
program is loaded and provide new instructions with the prologue.

We replace this function/ality by taking instructions for specific
program, attaching prologue to them and load such new ebpf programs
with prologue using separate bpf_prog_load calls (outside libbpf
load machinery).

Before we can take and use program instructions, we need libbpf to
actually load it. This way we get the final shape of its instructions
with all relocations and verifier adjustments).

There's one glitch though.. perf kprobe program already assumes
generated prologue code with proper values in argument registers,
so loading such program directly will fail in the verifier.

That's where the fallback pre-load handler fits in and prepends
the initialization code to the program. Once such program is loaded
we take its instructions, cut off the initialization code and prepend
the prologue.

I know.. sorry ;-)

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/perf/util/bpf-loader.c | 128 ++++++++++++++++++++++++++++++-----
 1 file changed, 110 insertions(+), 18 deletions(-)

diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
index e7992a0eb477..2ce5f9684863 100644
--- a/tools/perf/util/bpf-loader.c
+++ b/tools/perf/util/bpf-loader.c
@@ -9,6 +9,7 @@
 #include <linux/bpf.h>
 #include <bpf/libbpf.h>
 #include <bpf/bpf.h>
+#include <linux/filter.h>
 #include <linux/err.h>
 #include <linux/kernel.h>
 #include <linux/string.h>
@@ -49,6 +50,7 @@ struct bpf_prog_priv {
 	struct bpf_insn *insns_buf;
 	int nr_types;
 	int *type_mapping;
+	int *proglogue_fds;
 };
 
 struct bpf_perf_object {
@@ -56,6 +58,11 @@ struct bpf_perf_object {
 	struct bpf_object *obj;
 };
 
+struct bpf_preproc_result {
+	struct bpf_insn *new_insn_ptr;
+	int new_insn_cnt;
+};
+
 static LIST_HEAD(bpf_objects_list);
 static struct hashmap *bpf_program_hash;
 static struct hashmap *bpf_map_hash;
@@ -233,14 +240,31 @@ struct bpf_object *bpf__prepare_load(const char *filename, bool source)
 	return obj;
 }
 
+static void close_prologue_programs(struct bpf_prog_priv *priv)
+{
+	struct perf_probe_event *pev;
+	int i, fd;
+
+	if (!priv->need_prologue)
+		return;
+	pev = &priv->pev;
+	for (i = 0; i < pev->ntevs; i++) {
+		fd = priv->proglogue_fds[i];
+		if (fd != -1)
+			close(fd);
+	}
+}
+
 static void
 clear_prog_priv(const struct bpf_program *prog __maybe_unused,
 		void *_priv)
 {
 	struct bpf_prog_priv *priv = _priv;
 
+	close_prologue_programs(priv);
 	cleanup_perf_probe_events(&priv->pev, 1);
 	zfree(&priv->insns_buf);
+	zfree(&priv->proglogue_fds);
 	zfree(&priv->type_mapping);
 	zfree(&priv->sys_name);
 	zfree(&priv->evt_name);
@@ -603,8 +627,8 @@ static int bpf__prepare_probe(void)
 
 static int
 preproc_gen_prologue(struct bpf_program *prog, int n,
-		     struct bpf_insn *orig_insns, int orig_insns_cnt,
-		     struct bpf_prog_prep_result *res)
+		     const struct bpf_insn *orig_insns, int orig_insns_cnt,
+		     struct bpf_preproc_result *res)
 {
 	struct bpf_prog_priv *priv = program_priv(prog);
 	struct probe_trace_event *tev;
@@ -652,7 +676,6 @@ preproc_gen_prologue(struct bpf_program *prog, int n,
 
 	res->new_insn_ptr = buf;
 	res->new_insn_cnt = prologue_cnt + orig_insns_cnt;
-	res->pfd = NULL;
 	return 0;
 
 errout:
@@ -760,7 +783,7 @@ static int hook_load_preprocessor(struct bpf_program *prog)
 	struct bpf_prog_priv *priv = program_priv(prog);
 	struct perf_probe_event *pev;
 	bool need_prologue = false;
-	int err, i;
+	int i;
 
 	if (IS_ERR_OR_NULL(priv)) {
 		pr_debug("Internal error when hook preprocessor\n");
@@ -798,6 +821,13 @@ static int hook_load_preprocessor(struct bpf_program *prog)
 		return -ENOMEM;
 	}
 
+	priv->proglogue_fds = malloc(sizeof(int) * pev->ntevs);
+	if (!priv->proglogue_fds) {
+		pr_debug("Not enough memory: alloc prologue fds failed\n");
+		return -ENOMEM;
+	}
+	memset(priv->proglogue_fds, -1, sizeof(int) * pev->ntevs);
+
 	priv->type_mapping = malloc(sizeof(int) * pev->ntevs);
 	if (!priv->type_mapping) {
 		pr_debug("Not enough memory: alloc type_mapping failed\n");
@@ -806,13 +836,7 @@ static int hook_load_preprocessor(struct bpf_program *prog)
 	memset(priv->type_mapping, -1,
 	       sizeof(int) * pev->ntevs);
 
-	err = map_prologue(pev, priv->type_mapping, &priv->nr_types);
-	if (err)
-		return err;
-
-	err = bpf_program__set_prep(prog, priv->nr_types,
-				    preproc_gen_prologue);
-	return err;
+	return map_prologue(pev, priv->type_mapping, &priv->nr_types);
 }
 
 int bpf__probe(struct bpf_object *obj)
@@ -919,6 +943,77 @@ int bpf__unprobe(struct bpf_object *obj)
 	return ret;
 }
 
+static int bpf_object__load_prologue(struct bpf_object *obj)
+{
+	int init_cnt = ARRAY_SIZE(prologue_init_insn);
+	const struct bpf_insn *orig_insns;
+	struct bpf_preproc_result res;
+	struct perf_probe_event *pev;
+	struct bpf_program *prog;
+	int orig_insns_cnt;
+
+	bpf_object__for_each_program(prog, obj) {
+		struct bpf_prog_priv *priv = program_priv(prog);
+		int err, i, fd;
+
+		if (IS_ERR_OR_NULL(priv)) {
+			pr_debug("bpf: failed to get private field\n");
+			return -BPF_LOADER_ERRNO__INTERNAL;
+		}
+
+		if (!priv->need_prologue)
+			continue;
+
+		/*
+		 * For each program that needs prologue we do following:
+		 *
+		 * - take its current instructions and use them
+		 *   to generate the new code with prologue
+		 * - load new instructions with bpf_prog_load
+		 *   and keep the fd in proglogue_fds
+		 * - new fd will be used in bpf__foreach_event
+		 *   to connect this program with perf evsel
+		 */
+		orig_insns = bpf_program__insns(prog);
+		orig_insns_cnt = bpf_program__insn_cnt(prog);
+
+		pev = &priv->pev;
+		for (i = 0; i < pev->ntevs; i++) {
+			/*
+			 * Skipping artificall prologue_init_insn instructions
+			 * (init_cnt), so the prologue can be generated instead
+			 * of them.
+			 */
+			err = preproc_gen_prologue(prog, i,
+						   orig_insns + init_cnt,
+						   orig_insns_cnt - init_cnt,
+						   &res);
+			if (err)
+				return err;
+
+			fd = bpf_prog_load(bpf_program__get_type(prog),
+					   bpf_program__name(prog), "GPL",
+					   res.new_insn_ptr,
+					   res.new_insn_cnt, NULL);
+			if (fd < 0) {
+				char bf[128];
+
+				libbpf_strerror(-errno, bf, sizeof(bf));
+				pr_debug("bpf: load objects with prologue failed: err=%d: (%s)\n",
+					 -errno, bf);
+				return -errno;
+			}
+			priv->proglogue_fds[i] = fd;
+		}
+		/*
+		 * We no longer need the original program,
+		 * we can unload it.
+		 */
+		bpf_program__unload(prog);
+	}
+	return 0;
+}
+
 int bpf__load(struct bpf_object *obj)
 {
 	int err;
@@ -930,7 +1025,7 @@ int bpf__load(struct bpf_object *obj)
 		pr_debug("bpf: load objects failed: err=%d: (%s)\n", err, bf);
 		return err;
 	}
-	return 0;
+	return bpf_object__load_prologue(obj);
 }
 
 int bpf__foreach_event(struct bpf_object *obj,
@@ -965,13 +1060,10 @@ int bpf__foreach_event(struct bpf_object *obj,
 		for (i = 0; i < pev->ntevs; i++) {
 			tev = &pev->tevs[i];
 
-			if (priv->need_prologue) {
-				int type = priv->type_mapping[i];
-
-				fd = bpf_program__nth_fd(prog, type);
-			} else {
+			if (priv->need_prologue)
+				fd = priv->proglogue_fds[i];
+			else
 				fd = bpf_program__fd(prog);
-			}
 
 			if (fd < 0) {
 				pr_debug("bpf: failed to get file descriptor\n");
-- 
2.35.3

Re: [PATCHv3 bpf-next 2/2] perf tools: Rework prologue generation code

[Andrii Nakryiko]

On Fri, Jun 3, 2022 at 2:21 AM Jiri Olsa <jolsa@kernel.org> wrote:
>
> Some functions we use for bpf prologue generation are going to be
> deprecated. This change reworks current code not to use them.
>
> We need to replace following functions/struct:
>    bpf_program__set_prep
>    bpf_program__nth_fd
>    struct bpf_prog_prep_result
>
> Currently we use bpf_program__set_prep to hook perf callback before
> program is loaded and provide new instructions with the prologue.
>
> We replace this function/ality by taking instructions for specific
> program, attaching prologue to them and load such new ebpf programs
> with prologue using separate bpf_prog_load calls (outside libbpf
> load machinery).
>
> Before we can take and use program instructions, we need libbpf to
> actually load it. This way we get the final shape of its instructions
> with all relocations and verifier adjustments).
>
> There's one glitch though.. perf kprobe program already assumes
> generated prologue code with proper values in argument registers,
> so loading such program directly will fail in the verifier.
>
> That's where the fallback pre-load handler fits in and prepends
> the initialization code to the program. Once such program is loaded
> we take its instructions, cut off the initialization code and prepend
> the prologue.
>
> I know.. sorry ;-)
>
> Suggested-by: Andrii Nakryiko <andrii@kernel.org>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>  tools/perf/util/bpf-loader.c | 128 ++++++++++++++++++++++++++++++-----
>  1 file changed, 110 insertions(+), 18 deletions(-)
>
> diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
> index e7992a0eb477..2ce5f9684863 100644
> --- a/tools/perf/util/bpf-loader.c
> +++ b/tools/perf/util/bpf-loader.c
> @@ -9,6 +9,7 @@
>  #include <linux/bpf.h>
>  #include <bpf/libbpf.h>
>  #include <bpf/bpf.h>
> +#include <linux/filter.h>
>  #include <linux/err.h>
>  #include <linux/kernel.h>
>  #include <linux/string.h>
> @@ -49,6 +50,7 @@ struct bpf_prog_priv {
>         struct bpf_insn *insns_buf;
>         int nr_types;
>         int *type_mapping;
> +       int *proglogue_fds;

massively copy/pasted typo? prologue_fds?

Other than that looks good to me, but we'll need Arnaldo's ack before
merging into bpf-next.

>  };
>
>  struct bpf_perf_object {
> @@ -56,6 +58,11 @@ struct bpf_perf_object {
>         struct bpf_object *obj;
>  };
>

[...]

Re: [PATCHv3 bpf-next 2/2] perf tools: Rework prologue generation code

[Jiri Olsa]

On Fri, Jun 03, 2022 at 11:46:52AM -0700, Andrii Nakryiko wrote:
> On Fri, Jun 3, 2022 at 2:21 AM Jiri Olsa <jolsa@kernel.org> wrote:
> >
> > Some functions we use for bpf prologue generation are going to be
> > deprecated. This change reworks current code not to use them.
> >
> > We need to replace following functions/struct:
> >    bpf_program__set_prep
> >    bpf_program__nth_fd
> >    struct bpf_prog_prep_result
> >
> > Currently we use bpf_program__set_prep to hook perf callback before
> > program is loaded and provide new instructions with the prologue.
> >
> > We replace this function/ality by taking instructions for specific
> > program, attaching prologue to them and load such new ebpf programs
> > with prologue using separate bpf_prog_load calls (outside libbpf
> > load machinery).
> >
> > Before we can take and use program instructions, we need libbpf to
> > actually load it. This way we get the final shape of its instructions
> > with all relocations and verifier adjustments).
> >
> > There's one glitch though.. perf kprobe program already assumes
> > generated prologue code with proper values in argument registers,
> > so loading such program directly will fail in the verifier.
> >
> > That's where the fallback pre-load handler fits in and prepends
> > the initialization code to the program. Once such program is loaded
> > we take its instructions, cut off the initialization code and prepend
> > the prologue.
> >
> > I know.. sorry ;-)
> >
> > Suggested-by: Andrii Nakryiko <andrii@kernel.org>
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> >  tools/perf/util/bpf-loader.c | 128 ++++++++++++++++++++++++++++++-----
> >  1 file changed, 110 insertions(+), 18 deletions(-)
> >
> > diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
> > index e7992a0eb477..2ce5f9684863 100644
> > --- a/tools/perf/util/bpf-loader.c
> > +++ b/tools/perf/util/bpf-loader.c
> > @@ -9,6 +9,7 @@
> >  #include <linux/bpf.h>
> >  #include <bpf/libbpf.h>
> >  #include <bpf/bpf.h>
> > +#include <linux/filter.h>
> >  #include <linux/err.h>
> >  #include <linux/kernel.h>
> >  #include <linux/string.h>
> > @@ -49,6 +50,7 @@ struct bpf_prog_priv {
> >         struct bpf_insn *insns_buf;
> >         int nr_types;
> >         int *type_mapping;
> > +       int *proglogue_fds;
> 
> massively copy/pasted typo? prologue_fds?

mama mia :)) time to have my eyes checked..  sry, I'll send new version

jirka

> 
> Other than that looks good to me, but we'll need Arnaldo's ack before
> merging into bpf-next.
> 
> >  };
> >
> >  struct bpf_perf_object {
> > @@ -56,6 +58,11 @@ struct bpf_perf_object {
> >         struct bpf_object *obj;
> >  };
> >
> 
> [...]