Re: [RFT] Testing 1.22

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Em Thu, May 27, 2021 at 01:41:13PM -0700, Andrii Nakryiko escreveu:
> On Thu, May 27, 2021 at 12:57 PM Arnaldo <arnaldo.melo@xxxxxxxxx> wrote:
> > On May 27, 2021 4:14:17 PM GMT-03:00, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:
> > >If we make 1.22 mandatory there will be no good reason to make 1.23
> > >mandatory again. So I will have absolutely no inclination to work on
> > >this, for example. So we are just wasting a chance to clean up the
> > >Kbuild story w.r.t. pahole. And we are talking about just a few days
> > >at most, while we do have a reasonable work around on the kernel side.

> > So there were patches for stop using objcopy, which we thought could
> > uncover some can of worms, were there patches for the detached BTF
> > file?
 
> No, there weren't, if I remember correctly. What's the concern,
> though? That detached BTF file isn't even an ELF, so it's
> btf__get_raw_data() and write it to the file. Done.

See patch below, lightly tested, now working on making pahole accept raw
BTF files out of /sys/kernel/btf/

Please test, and if works as expected, try to bolt this into the kbuild
process, as intended.

- Arnaldo

commit b579a18a1ea0ee84b90b5302f597dda2edf2f61b
Author: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Date:   Fri May 28 16:41:30 2021 -0300

    pahole: Allow encoding BTF into a detached file
    
    Previously the newly encoded BTF info was stored into a ELF section in
    the file where the DWARF info was obtained, but it is useful to just
    dump it into a separate file, do it.
    
    Requested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
    Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

diff --git a/btf_encoder.c b/btf_encoder.c
index 033c927b537dad1e..bc3ac72968cea826 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -21,6 +21,14 @@
 #include <stdlib.h> /* for qsort() and bsearch() */
 #include <inttypes.h>
 
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include <unistd.h>
+
+#include <errno.h>
+
 /*
  * This corresponds to the same macro defined in
  * include/linux/kallsyms.h
@@ -267,14 +275,62 @@ static struct btf_elf *btfe;
 static uint32_t array_index_id;
 static bool has_index_type;
 
-int btf_encoder__encode()
+static int btf_encoder__dump(struct btf *btf, const char *filename)
+{
+	uint32_t raw_btf_size;
+	const void *raw_btf_data;
+	int fd, err;
+
+	/* Empty file, nothing to do, so... done! */
+	if (btf__get_nr_types(btf) == 0)
+		return 0;
+
+	if (btf__dedup(btf, NULL, NULL)) {
+		fprintf(stderr, "%s: btf__dedup failed!\n", __func__);
+		return -1;
+	}
+
+	raw_btf_data = btf__get_raw_data(btf, &raw_btf_size);
+	if (raw_btf_data == NULL) {
+                fprintf(stderr, "%s: btf__get_raw_data failed!\n", __func__);
+		return -1;
+	}
+
+	fd = open(filename, O_WRONLY | O_CREAT);
+	if (fd < 0) {
+                fprintf(stderr, "%s: Couldn't open %s for writing the raw BTF info: %s\n", __func__, filename, strerror(errno));
+		return -1;
+	}
+	err = write(fd, raw_btf_data, raw_btf_size);
+	if (err < 0)
+                fprintf(stderr, "%s: Couldn't open %s for writing the raw BTF info: %s\n", __func__, filename, strerror(errno));
+
+	close(fd);
+
+	if (err != raw_btf_size) {
+                fprintf(stderr, "%s: Could only write %d bytes to %s of raw BTF info out of %d, aborting\n", __func__, err, filename, raw_btf_size);
+		unlink(filename);
+		err = -1;
+	} else {
+		/* go from bytes written == raw_btf_size to an indication that all went fine */
+		err = 0;
+	}
+
+	return err;
+}
+
+int btf_encoder__encode(const char *filename)
 {
 	int err;
 
 	if (gobuffer__size(&btfe->percpu_secinfo) != 0)
 		btf_elf__add_datasec_type(btfe, PERCPU_SECTION, &btfe->percpu_secinfo);
 
-	err = btf_elf__encode(btfe, 0);
+	if (filename == NULL)
+		err = btf_elf__encode(btfe, 0);
+	else
+		err = btf_encoder__dump(btfe->btf, filename);
+
 	delete_functions();
 	btf_elf__delete(btfe);
 	btfe = NULL;
@@ -412,7 +468,7 @@ static bool has_arg_names(struct cu *cu, struct ftype *ftype)
 }
 
 int cu__encode_btf(struct cu *cu, int verbose, bool force,
-		   bool skip_encoding_vars)
+		   bool skip_encoding_vars, const char *detached_btf_filename)
 {
 	uint32_t type_id_off;
 	uint32_t core_id;
@@ -425,7 +481,7 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force,
 	btf_elf__force = force;
 
 	if (btfe && strcmp(btfe->filename, cu->filename)) {
-		err = btf_encoder__encode();
+		err = btf_encoder__encode(detached_btf_filename);
 		if (err)
 			goto out;
 
diff --git a/btf_encoder.h b/btf_encoder.h
index 46fb2312fc0eea9b..bfc6085092028adc 100644
--- a/btf_encoder.h
+++ b/btf_encoder.h
@@ -11,9 +11,9 @@
 
 struct cu;
 
-int btf_encoder__encode();
+int btf_encoder__encode(const char *filename);
 
 int cu__encode_btf(struct cu *cu, int verbose, bool force,
-		   bool skip_encoding_vars);
+		   bool skip_encoding_vars, const char *detached_btf_filename);
 
 #endif /* _BTF_ENCODER_H_ */
diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
index 2659fe6f231405d8..6e7ded59595f5ea7 100644
--- a/man-pages/pahole.1
+++ b/man-pages/pahole.1
@@ -189,6 +189,10 @@ features such as BPF CO-RE (Compile Once - Run Everywhere).
 
 See \fIhttps://nakryiko.com/posts/bpf-portability-and-co-re/\fR.
 
+.TP
+.B \-j, \-\-btf_encode_detached=FILENAME
+Same thing as -J/--btf_encode, but storing the raw BTF info into a separate file.
+
 .TP
 .B \-\-btf_encode_force
 Ignore those symbols found invalid when encoding BTF.
diff --git a/pahole.c b/pahole.c
index 24659e2969c8fb85..1cbff6175b60af51 100644
--- a/pahole.c
+++ b/pahole.c
@@ -26,6 +26,7 @@
 #include "lib/bpf/src/libbpf.h"
 #include "pahole_strings.h"
 
+static char *detached_btf_filename;
 static bool btf_encode;
 static bool ctf_encode;
 static bool first_obj_only;
@@ -1152,6 +1153,12 @@ static const struct argp_option pahole__options[] = {
 		.key  = 'J',
 		.doc  = "Encode as BTF",
 	},
+	{
+		.name = "btf_encode_detached",
+		.key  = 'j',
+		.arg  = "FILENAME",
+		.doc  = "Encode as BTF in a detached file",
+	},
 	{
 		.name = "skip_encoding_btf_vars",
 		.key  = ARGP_skip_encoding_btf_vars,
@@ -1223,6 +1230,7 @@ static error_t pahole__options_parser(int key, char *arg,
 		  conf_load.extra_dbg_info = 1;		break;
 	case 'i': find_containers = 1;
 		  class_name = arg;			break;
+	case 'j': detached_btf_filename = arg; // fallthru
 	case 'J': btf_encode = 1;
 		  conf_load.get_addr_info = true;
 		  no_bitfield_type_recode = true;	break;
@@ -2458,7 +2466,7 @@ static enum load_steal_kind pahole_stealer(struct cu *cu,
 
 	if (btf_encode) {
 		if (cu__encode_btf(cu, global_verbose, btf_encode_force,
-				   skip_encoding_btf_vars)) {
+				   skip_encoding_btf_vars, detached_btf_filename)) {
 			fprintf(stderr, "Encountered error while encoding BTF.\n");
 			exit(1);
 		}
@@ -2872,7 +2880,7 @@ try_sole_arg_as_class_names:
 	header = NULL;
 
 	if (btf_encode) {
-		err = btf_encoder__encode();
+		err = btf_encoder__encode(detached_btf_filename);
 		if (err) {
 			fputs("Failed to encode BTF\n", stderr);
 			goto out_cus_delete;



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