[PATCH dwarves 0/4] Add split BTF support to pahole

[PATCH dwarves 0/4] Add split BTF support to pahole

[Andrii Nakryiko]

Add ability to generate split BTF (for kernel modules), as well as load split
BTF. --btf_base argument is added to specify base BTF for split BTF. This
works for both btf_loader and btf_encoder.

Andrii Nakryiko (4):
  btf_encoder: fix array index type numbering
  libbtf: improve variable naming and error reporting when writing out
    BTF
  libbpf: update libbpf submodlue reference to latest master
  btf: add support for split BTF loading and encoding

 btf_encoder.c | 15 ++++++++-------
 btf_loader.c  |  2 +-
 lib/bpf       |  2 +-
 libbtf.c      | 43 +++++++++++++++++++++++++++----------------
 libbtf.h      |  4 +++-
 pahole.c      | 23 +++++++++++++++++++++++
 6 files changed, 63 insertions(+), 26 deletions(-)

-- 
2.24.1

[PATCH dwarves 1/4] btf_encoder: fix array index type numbering

[Andrii Nakryiko]

Take into account type ID offset, accumulated from previous CUs, when
calculating a new type ID for the generated array index type.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 btf_encoder.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/btf_encoder.c b/btf_encoder.c
index 4c92908beab2..b3e47f172bb3 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -358,22 +358,22 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force,
 			printf("File %s:\n", btfe->filename);
 	}
 
+	btf_elf__verbose = verbose;
+	btf_elf__force = force;
+	type_id_off = btf__get_nr_types(btfe->btf);
+
 	if (!has_index_type) {
 		/* cu__find_base_type_by_name() takes "type_id_t *id" */
 		type_id_t id;
 		if (cu__find_base_type_by_name(cu, "int", &id)) {
 			has_index_type = true;
-			array_index_id = id;
+			array_index_id = type_id_off + id;
 		} else {
 			has_index_type = false;
-			array_index_id = cu->types_table.nr_entries;
+			array_index_id = type_id_off + cu->types_table.nr_entries;
 		}
 	}
 
-	btf_elf__verbose = verbose;
-	btf_elf__force = force;
-	type_id_off = btf__get_nr_types(btfe->btf);
-
 	cu__for_each_type(cu, core_id, pos) {
 		int32_t btf_type_id = tag__encode_btf(cu, pos, core_id, btfe, array_index_id, type_id_off);
 
-- 
2.24.1

[PATCH dwarves 2/4] libbtf: improve variable naming and error reporting when writing out BTF

[Andrii Nakryiko]

Rename few local variables to reflects the purpose a bit better. Also separate
writing out BTF raw data and objcopy invocation into two separate steps and
improve error reporting for each.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 libbtf.c | 33 +++++++++++++++++++++------------
 1 file changed, 21 insertions(+), 12 deletions(-)

diff --git a/libbtf.c b/libbtf.c
index babf4fe8cd9e..b6ddd7599395 100644
--- a/libbtf.c
+++ b/libbtf.c
@@ -679,11 +679,11 @@ static int btf_elf__write(const char *filename, struct btf *btf)
 {
 	GElf_Shdr shdr_mem, *shdr;
 	GElf_Ehdr ehdr_mem, *ehdr;
-	Elf_Data *btf_elf = NULL;
+	Elf_Data *btf_data = NULL;
 	Elf_Scn *scn = NULL;
 	Elf *elf = NULL;
-	const void *btf_data;
-	uint32_t btf_size;
+	const void *raw_btf_data;
+	uint32_t raw_btf_size;
 	int fd, err = -1;
 	size_t strndx;
 
@@ -735,18 +735,18 @@ static int btf_elf__write(const char *filename, struct btf *btf)
 			continue;
 		char *secname = elf_strptr(elf, strndx, shdr->sh_name);
 		if (strcmp(secname, ".BTF") == 0) {
-			btf_elf = elf_getdata(scn, btf_elf);
+			btf_data = elf_getdata(scn, btf_data);
 			break;
 		}
 	}
 
-	btf_data = btf__get_raw_data(btf, &btf_size);
+	raw_btf_data = btf__get_raw_data(btf, &raw_btf_size);
 
-	if (btf_elf) {
+	if (btf_data) {
 		/* Exisiting .BTF section found */
-		btf_elf->d_buf = (void *)btf_data;
-		btf_elf->d_size = btf_size;
-		elf_flagdata(btf_elf, ELF_C_SET, ELF_F_DIRTY);
+		btf_data->d_buf = (void *)raw_btf_data;
+		btf_data->d_size = raw_btf_size;
+		elf_flagdata(btf_data, ELF_C_SET, ELF_F_DIRTY);
 
 		if (elf_update(elf, ELF_C_NULL) >= 0 &&
 		    elf_update(elf, ELF_C_WRITE) >= 0)
@@ -770,12 +770,21 @@ static int btf_elf__write(const char *filename, struct btf *btf)
 			goto out;
 		}
 
+		if (write(fd, raw_btf_data, raw_btf_size) != raw_btf_size) {
+			fprintf(stderr, "%s: write of %d bytes to '%s' failed: %d!\n",
+				__func__, raw_btf_size, tmp_fn, errno);
+			goto out;
+		}
+
 		snprintf(cmd, sizeof(cmd), "%s --add-section .BTF=%s %s",
 			 llvm_objcopy, tmp_fn, filename);
+		if (system(cmd)) {
+			fprintf(stderr, "%s: failed to add .BTF section to '%s': %d!\n",
+				__func__, tmp_fn, errno);
+			goto out;
+		}
 
-		if (write(fd, btf_data, btf_size) == btf_size && !system(cmd))
-			err = 0;
-
+		err = 0;
 		unlink(tmp_fn);
 	}
 
-- 
2.24.1

[PATCH dwarves 3/4] libbpf: update libbpf submodlue reference to latest master

[Andrii Nakryiko]

Pull in latest libbpf changes, containing split BTF APIs.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 lib/bpf | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/bpf b/lib/bpf
index ff797cc905d9..5af3d86b5a2c 160000
--- a/lib/bpf
+++ b/lib/bpf
@@ -1 +1 @@
-Subproject commit ff797cc905d9c5fe9acab92d2da127342b20f80f
+Subproject commit 5af3d86b5a2c5fecdc3ab83822d083edd32b4396
-- 
2.24.1

[PATCH dwarves 4/4] btf: add support for split BTF loading and encoding

[Andrii Nakryiko]

Add support for generating split BTF, in which there is a designated base
BTF, containing a base set of types, and a split BTF, which extends main BTF
with extra types, that can reference types and strings from the main BTF.

This is going to be used to generate compact BTFs for kernel modules, with
vmlinux BTF being a main BTF, which all kernel modules are based off of.

These changes rely on patch set [0] to be present in libbpf submodule.

  [0] https://patchwork.kernel.org/project/netdevbpf/list/?series=377859&state=*

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 btf_encoder.c |  3 ++-
 btf_loader.c  |  2 +-
 libbtf.c      | 10 ++++++----
 libbtf.h      |  4 +++-
 pahole.c      | 23 +++++++++++++++++++++++
 5 files changed, 35 insertions(+), 7 deletions(-)

diff --git a/btf_encoder.c b/btf_encoder.c
index b3e47f172bb3..d67e29b9cbee 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -12,6 +12,7 @@
 #include "dwarves.h"
 #include "libbtf.h"
 #include "lib/bpf/include/uapi/linux/btf.h"
+#include "lib/bpf/src/libbpf.h"
 #include "hash.h"
 #include "elf_symtab.h"
 #include "btf_encoder.h"
@@ -343,7 +344,7 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force,
 	}
 
 	if (!btfe) {
-		btfe = btf_elf__new(cu->filename, cu->elf);
+		btfe = btf_elf__new(cu->filename, cu->elf, base_btf);
 		if (!btfe)
 			return -1;
 
diff --git a/btf_loader.c b/btf_loader.c
index 6ea207ea65b4..ec286f413f36 100644
--- a/btf_loader.c
+++ b/btf_loader.c
@@ -534,7 +534,7 @@ struct debug_fmt_ops btf_elf__ops;
 int btf_elf__load_file(struct cus *cus, struct conf_load *conf, const char *filename)
 {
 	int err;
-	struct btf_elf *btfe = btf_elf__new(filename, NULL);
+	struct btf_elf *btfe = btf_elf__new(filename, NULL, base_btf);
 
 	if (btfe == NULL)
 		return -1;
diff --git a/libbtf.c b/libbtf.c
index b6ddd7599395..3c52aa0d482b 100644
--- a/libbtf.c
+++ b/libbtf.c
@@ -27,6 +27,7 @@
 #include "dwarves.h"
 #include "elf_symtab.h"
 
+struct btf *base_btf;
 uint8_t btf_elf__verbose;
 uint8_t btf_elf__force;
 
@@ -52,9 +53,9 @@ int btf_elf__load(struct btf_elf *btfe)
 	/* free initial empty BTF */
 	btf__free(btfe->btf);
 	if (btfe->raw_btf)
-		btfe->btf = btf__parse_raw(btfe->filename);
+		btfe->btf = btf__parse_raw_split(btfe->filename, btfe->base_btf);
 	else
-		btfe->btf = btf__parse_elf(btfe->filename, NULL);
+		btfe->btf = btf__parse_elf_split(btfe->filename, btfe->base_btf);
 
 	err = libbpf_get_error(btfe->btf);
 	if (err)
@@ -63,7 +64,7 @@ int btf_elf__load(struct btf_elf *btfe)
 	return 0;
 }
 
-struct btf_elf *btf_elf__new(const char *filename, Elf *elf)
+struct btf_elf *btf_elf__new(const char *filename, Elf *elf, struct btf *base_btf)
 {
 	struct btf_elf *btfe = zalloc(sizeof(*btfe));
 	GElf_Shdr shdr;
@@ -77,7 +78,8 @@ struct btf_elf *btf_elf__new(const char *filename, Elf *elf)
 	if (btfe->filename == NULL)
 		goto errout;
 
-	btfe->btf = btf__new_empty();
+	btfe->base_btf = base_btf;
+	btfe->btf = btf__new_empty_split(base_btf);
 	if (libbpf_get_error(btfe->btf)) {
 		fprintf(stderr, "%s: failed to create empty BTF.\n", __func__);
 		goto errout;
diff --git a/libbtf.h b/libbtf.h
index 887b5bc55c8e..71f6cecbea93 100644
--- a/libbtf.h
+++ b/libbtf.h
@@ -27,8 +27,10 @@ struct btf_elf {
 	uint32_t	  percpu_shndx;
 	uint64_t	  percpu_base_addr;
 	struct btf	  *btf;
+	struct btf	  *base_btf;
 };
 
+extern struct btf *base_btf;
 extern uint8_t btf_elf__verbose;
 extern uint8_t btf_elf__force;
 #define btf_elf__verbose_log(fmt, ...) { if (btf_elf__verbose) printf(fmt, __VA_ARGS__); }
@@ -39,7 +41,7 @@ struct cu;
 struct base_type;
 struct ftype;
 
-struct btf_elf *btf_elf__new(const char *filename, Elf *elf);
+struct btf_elf *btf_elf__new(const char *filename, Elf *elf, struct btf *base_btf);
 void btf_elf__delete(struct btf_elf *btf);
 
 int32_t btf_elf__add_base_type(struct btf_elf *btf, const struct base_type *bt,
diff --git a/pahole.c b/pahole.c
index bd9b993777ee..d18092c1212c 100644
--- a/pahole.c
+++ b/pahole.c
@@ -22,12 +22,15 @@
 #include "dutil.h"
 #include "ctf_encoder.h"
 #include "btf_encoder.h"
+#include "libbtf.h"
+#include "lib/bpf/src/libbpf.h"
 
 static bool btf_encode;
 static bool ctf_encode;
 static bool first_obj_only;
 static bool skip_encoding_btf_vars;
 static bool btf_encode_force;
+static const char *base_btf_file;
 
 static uint8_t class__include_anonymous;
 static uint8_t class__include_nested_anonymous;
@@ -820,6 +823,7 @@ ARGP_PROGRAM_VERSION_HOOK_DEF = dwarves_print_version;
 #define ARGP_skip_encoding_btf_vars 317
 #define ARGP_btf_encode_force	   318
 #define ARGP_just_packed_structs   319
+#define ARGP_btf_base		   320
 
 static const struct argp_option pahole__options[] = {
 	{
@@ -1093,6 +1097,12 @@ static const struct argp_option pahole__options[] = {
 		.key  = ARGP_hex_fmt,
 		.doc  = "Print offsets and sizes in hexadecimal",
 	},
+	{
+		.name = "btf_base",
+		.key  = ARGP_btf_base,
+		.arg  = "SIZE",
+		.doc  = "Path to the base BTF file",
+	},
 	{
 		.name = "btf_encode",
 		.key  = 'J',
@@ -1234,6 +1244,9 @@ static error_t pahole__options_parser(int key, char *arg,
 		skip_encoding_btf_vars = true;		break;
 	case ARGP_btf_encode_force:
 		btf_encode_force = true;		break;
+	case ARGP_btf_base:
+		base_btf_file = arg;
+		break;
 	default:
 		return ARGP_ERR_UNKNOWN;
 	}
@@ -2682,6 +2695,15 @@ int main(int argc, char *argv[])
 		goto out;
 	}
 
+	if (base_btf_file) {
+		base_btf = btf__parse(base_btf_file, NULL);
+		if (libbpf_get_error(base_btf)) {
+			fprintf(stderr, "Failed to parse base BTF '%s': %ld\n",
+				base_btf_file, libbpf_get_error(base_btf));
+			goto out;
+		}
+	}
+
 	struct cus *cus = cus__new();
 	if (cus == NULL) {
 		fputs("pahole: insufficient memory\n", stderr);
@@ -2766,6 +2788,7 @@ out_cus_delete:
 #ifdef DEBUG_CHECK_LEAKS
 	cus__delete(cus);
 	structures__delete();
+	btf__free(base_btf);
 #endif
 out_dwarves_exit:
 #ifdef DEBUG_CHECK_LEAKS
-- 
2.24.1

Re: [PATCH dwarves 0/4] Add split BTF support to pahole

[Andrii Nakryiko]

On Thu, Nov 5, 2020 at 9:25 PM Andrii Nakryiko <andrii@kernel.org> wrote:
>
> Add ability to generate split BTF (for kernel modules), as well as load split
> BTF. --btf_base argument is added to specify base BTF for split BTF. This
> works for both btf_loader and btf_encoder.

Arnaldo, can you please take a look at these patches? Would be nice to
get them landed ASAP so that we can start testing out kernel module
BTFs without locally applying patches first. Thanks!

>
> Andrii Nakryiko (4):
>   btf_encoder: fix array index type numbering
>   libbtf: improve variable naming and error reporting when writing out
>     BTF
>   libbpf: update libbpf submodlue reference to latest master
>   btf: add support for split BTF loading and encoding
>
>  btf_encoder.c | 15 ++++++++-------
>  btf_loader.c  |  2 +-
>  lib/bpf       |  2 +-
>  libbtf.c      | 43 +++++++++++++++++++++++++++----------------
>  libbtf.h      |  4 +++-
>  pahole.c      | 23 +++++++++++++++++++++++
>  6 files changed, 63 insertions(+), 26 deletions(-)
>
> --
> 2.24.1
>

Re: [PATCH dwarves 0/4] Add split BTF support to pahole

[Arnaldo]

On November 10, 2020 8:34:18 PM GMT-03:00, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
>On Thu, Nov 5, 2020 at 9:25 PM Andrii Nakryiko <andrii@kernel.org>
>wrote:
>>
>> Add ability to generate split BTF (for kernel modules), as well as
>load split
>> BTF. --btf_base argument is added to specify base BTF for split BTF.
>This
>> works for both btf_loader and btf_encoder.
>
>Arnaldo, can you please take a look at these patches? Would be nice to
>get them landed ASAP so that we can start testing out kernel module
>BTFs without locally applying patches first. Thanks!


I've been working on prepping up v1.19, will process these patches first thing in the morning, tomorrow,

Thanks,

- Arnaldo
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

Re: [PATCH dwarves 0/4] Add split BTF support to pahole

[Andrii Nakryiko]

On Tue, Nov 10, 2020 at 4:30 PM Arnaldo <arnaldo.melo@gmail.com> wrote:
>
>
>
> On November 10, 2020 8:34:18 PM GMT-03:00, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
> >On Thu, Nov 5, 2020 at 9:25 PM Andrii Nakryiko <andrii@kernel.org>
> >wrote:
> >>
> >> Add ability to generate split BTF (for kernel modules), as well as
> >load split
> >> BTF. --btf_base argument is added to specify base BTF for split BTF.
> >This
> >> works for both btf_loader and btf_encoder.
> >
> >Arnaldo, can you please take a look at these patches? Would be nice to
> >get them landed ASAP so that we can start testing out kernel module
> >BTFs without locally applying patches first. Thanks!
>
>
> I've been working on prepping up v1.19, will process these patches first thing in the morning, tomorrow,
>

Thanks! Do you plan to include these changes into v1.19 as well?


> Thanks,
>
> - Arnaldo
> --
> Sent from my Android device with K-9 Mail. Please excuse my brevity.

Re: [PATCH dwarves 0/4] Add split BTF support to pahole

[Arnaldo]

On November 10, 2020 9:35:25 PM GMT-03:00, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
>On Tue, Nov 10, 2020 at 4:30 PM Arnaldo <arnaldo.melo@gmail.com> wrote:
>> On November 10, 2020 8:34:18 PM GMT-03:00, Andrii Nakryiko
><andrii.nakryiko@gmail.com> wrote:
>> >On Thu, Nov 5, 2020 at 9:25 PM Andrii Nakryiko <andrii@kernel.org>
>> >wrote:
>> >>
>> >> Add ability to generate split BTF (for kernel modules), as well as
>> >load split
>> >> BTF. --btf_base argument is added to specify base BTF for split
>BTF.
>> >This
>> >> works for both btf_loader and btf_encoder.
>> >
>> >Arnaldo, can you please take a look at these patches? Would be nice
>to
>> >get them landed ASAP so that we can start testing out kernel module
>> >BTFs without locally applying patches first. Thanks!
>>
>>
>> I've been working on prepping up v1.19, will process these patches
>first thing in the morning, tomorrow,
>>
>
>Thanks! Do you plan to include these changes into v1.19 as well?


Lemme test it tomorrow morning.

- Arnaldo
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

Re: [PATCH dwarves 4/4] btf: add support for split BTF loading and encoding

[Arnaldo Carvalho de Melo]

Em Thu, Nov 05, 2020 at 09:25:49PM -0800, Andrii Nakryiko escreveu:
> Add support for generating split BTF, in which there is a designated base
> BTF, containing a base set of types, and a split BTF, which extends main BTF
> with extra types, that can reference types and strings from the main BTF.
 
> This is going to be used to generate compact BTFs for kernel modules, with
> vmlinux BTF being a main BTF, which all kernel modules are based off of.
 
> These changes rely on patch set [0] to be present in libbpf submodule.
 
>   [0] https://patchwork.kernel.org/project/netdevbpf/list/?series=377859&state=*

So, applied and added this:

diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
index 4b5e0a1bf5462b28..20ee91fc911d4b39 100644
--- a/man-pages/pahole.1
+++ b/man-pages/pahole.1
@@ -185,6 +185,10 @@ Do not encode VARs in BTF.
 .B \-\-btf_encode_force
 Ignore those symbols found invalid when encoding BTF.
 
+.TP
+.B \-\-btf_base
+Path to the base BTF file, for instance: vmlinux when encoding kernel module BTF information.
+
 .TP
 .B \-l, \-\-show_first_biggest_size_base_type_member
 Show first biggest size base_type member.

---------------

The entry for btf_encode/-J is missing, I'll add in a followup patch.

Also I had to fixup ARGP_btf_base to 321 as I added this, to simplify
the kernel scripts and Makefiles:

  $ pahole --numeric_version
  118
  $

Now to test this all by applying the kernel patches and the encoding
module BTF, looking at it, etc.

- Arnaldo
 
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---
>  btf_encoder.c |  3 ++-
>  btf_loader.c  |  2 +-
>  libbtf.c      | 10 ++++++----
>  libbtf.h      |  4 +++-
>  pahole.c      | 23 +++++++++++++++++++++++
>  5 files changed, 35 insertions(+), 7 deletions(-)
> 
> diff --git a/btf_encoder.c b/btf_encoder.c
> index b3e47f172bb3..d67e29b9cbee 100644
> --- a/btf_encoder.c
> +++ b/btf_encoder.c
> @@ -12,6 +12,7 @@
>  #include "dwarves.h"
>  #include "libbtf.h"
>  #include "lib/bpf/include/uapi/linux/btf.h"
> +#include "lib/bpf/src/libbpf.h"
>  #include "hash.h"
>  #include "elf_symtab.h"
>  #include "btf_encoder.h"
> @@ -343,7 +344,7 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force,
>  	}
>  
>  	if (!btfe) {
> -		btfe = btf_elf__new(cu->filename, cu->elf);
> +		btfe = btf_elf__new(cu->filename, cu->elf, base_btf);
>  		if (!btfe)
>  			return -1;
>  
> diff --git a/btf_loader.c b/btf_loader.c
> index 6ea207ea65b4..ec286f413f36 100644
> --- a/btf_loader.c
> +++ b/btf_loader.c
> @@ -534,7 +534,7 @@ struct debug_fmt_ops btf_elf__ops;
>  int btf_elf__load_file(struct cus *cus, struct conf_load *conf, const char *filename)
>  {
>  	int err;
> -	struct btf_elf *btfe = btf_elf__new(filename, NULL);
> +	struct btf_elf *btfe = btf_elf__new(filename, NULL, base_btf);
>  
>  	if (btfe == NULL)
>  		return -1;
> diff --git a/libbtf.c b/libbtf.c
> index b6ddd7599395..3c52aa0d482b 100644
> --- a/libbtf.c
> +++ b/libbtf.c
> @@ -27,6 +27,7 @@
>  #include "dwarves.h"
>  #include "elf_symtab.h"
>  
> +struct btf *base_btf;
>  uint8_t btf_elf__verbose;
>  uint8_t btf_elf__force;
>  
> @@ -52,9 +53,9 @@ int btf_elf__load(struct btf_elf *btfe)
>  	/* free initial empty BTF */
>  	btf__free(btfe->btf);
>  	if (btfe->raw_btf)
> -		btfe->btf = btf__parse_raw(btfe->filename);
> +		btfe->btf = btf__parse_raw_split(btfe->filename, btfe->base_btf);
>  	else
> -		btfe->btf = btf__parse_elf(btfe->filename, NULL);
> +		btfe->btf = btf__parse_elf_split(btfe->filename, btfe->base_btf);
>  
>  	err = libbpf_get_error(btfe->btf);
>  	if (err)
> @@ -63,7 +64,7 @@ int btf_elf__load(struct btf_elf *btfe)
>  	return 0;
>  }
>  
> -struct btf_elf *btf_elf__new(const char *filename, Elf *elf)
> +struct btf_elf *btf_elf__new(const char *filename, Elf *elf, struct btf *base_btf)
>  {
>  	struct btf_elf *btfe = zalloc(sizeof(*btfe));
>  	GElf_Shdr shdr;
> @@ -77,7 +78,8 @@ struct btf_elf *btf_elf__new(const char *filename, Elf *elf)
>  	if (btfe->filename == NULL)
>  		goto errout;
>  
> -	btfe->btf = btf__new_empty();
> +	btfe->base_btf = base_btf;
> +	btfe->btf = btf__new_empty_split(base_btf);
>  	if (libbpf_get_error(btfe->btf)) {
>  		fprintf(stderr, "%s: failed to create empty BTF.\n", __func__);
>  		goto errout;
> diff --git a/libbtf.h b/libbtf.h
> index 887b5bc55c8e..71f6cecbea93 100644
> --- a/libbtf.h
> +++ b/libbtf.h
> @@ -27,8 +27,10 @@ struct btf_elf {
>  	uint32_t	  percpu_shndx;
>  	uint64_t	  percpu_base_addr;
>  	struct btf	  *btf;
> +	struct btf	  *base_btf;
>  };
>  
> +extern struct btf *base_btf;
>  extern uint8_t btf_elf__verbose;
>  extern uint8_t btf_elf__force;
>  #define btf_elf__verbose_log(fmt, ...) { if (btf_elf__verbose) printf(fmt, __VA_ARGS__); }
> @@ -39,7 +41,7 @@ struct cu;
>  struct base_type;
>  struct ftype;
>  
> -struct btf_elf *btf_elf__new(const char *filename, Elf *elf);
> +struct btf_elf *btf_elf__new(const char *filename, Elf *elf, struct btf *base_btf);
>  void btf_elf__delete(struct btf_elf *btf);
>  
>  int32_t btf_elf__add_base_type(struct btf_elf *btf, const struct base_type *bt,
> diff --git a/pahole.c b/pahole.c
> index bd9b993777ee..d18092c1212c 100644
> --- a/pahole.c
> +++ b/pahole.c
> @@ -22,12 +22,15 @@
>  #include "dutil.h"
>  #include "ctf_encoder.h"
>  #include "btf_encoder.h"
> +#include "libbtf.h"
> +#include "lib/bpf/src/libbpf.h"
>  
>  static bool btf_encode;
>  static bool ctf_encode;
>  static bool first_obj_only;
>  static bool skip_encoding_btf_vars;
>  static bool btf_encode_force;
> +static const char *base_btf_file;
>  
>  static uint8_t class__include_anonymous;
>  static uint8_t class__include_nested_anonymous;
> @@ -820,6 +823,7 @@ ARGP_PROGRAM_VERSION_HOOK_DEF = dwarves_print_version;
>  #define ARGP_skip_encoding_btf_vars 317
>  #define ARGP_btf_encode_force	   318
>  #define ARGP_just_packed_structs   319
> +#define ARGP_btf_base		   320
>  
>  static const struct argp_option pahole__options[] = {
>  	{
> @@ -1093,6 +1097,12 @@ static const struct argp_option pahole__options[] = {
>  		.key  = ARGP_hex_fmt,
>  		.doc  = "Print offsets and sizes in hexadecimal",
>  	},
> +	{
> +		.name = "btf_base",
> +		.key  = ARGP_btf_base,
> +		.arg  = "SIZE",
> +		.doc  = "Path to the base BTF file",
> +	},
>  	{
>  		.name = "btf_encode",
>  		.key  = 'J',
> @@ -1234,6 +1244,9 @@ static error_t pahole__options_parser(int key, char *arg,
>  		skip_encoding_btf_vars = true;		break;
>  	case ARGP_btf_encode_force:
>  		btf_encode_force = true;		break;
> +	case ARGP_btf_base:
> +		base_btf_file = arg;
> +		break;
>  	default:
>  		return ARGP_ERR_UNKNOWN;
>  	}
> @@ -2682,6 +2695,15 @@ int main(int argc, char *argv[])
>  		goto out;
>  	}
>  
> +	if (base_btf_file) {
> +		base_btf = btf__parse(base_btf_file, NULL);
> +		if (libbpf_get_error(base_btf)) {
> +			fprintf(stderr, "Failed to parse base BTF '%s': %ld\n",
> +				base_btf_file, libbpf_get_error(base_btf));
> +			goto out;
> +		}
> +	}
> +
>  	struct cus *cus = cus__new();
>  	if (cus == NULL) {
>  		fputs("pahole: insufficient memory\n", stderr);
> @@ -2766,6 +2788,7 @@ out_cus_delete:
>  #ifdef DEBUG_CHECK_LEAKS
>  	cus__delete(cus);
>  	structures__delete();
> +	btf__free(base_btf);
>  #endif
>  out_dwarves_exit:
>  #ifdef DEBUG_CHECK_LEAKS
> -- 
> 2.24.1
> 

-- 

- Arnaldo

Re: [PATCH dwarves 4/4] btf: add support for split BTF loading and encoding

[Arnaldo Carvalho de Melo]

Em Wed, Nov 11, 2020 at 08:56:27AM -0300, Arnaldo Carvalho de Melo escreveu:
> 
> The entry for btf_encode/-J is missing, I'll add in a followup patch.
> 
> Also I had to fixup ARGP_btf_base to 321 as I added this, to simplify
> the kernel scripts and Makefiles:
> 
>   $ pahole --numeric_version
>   118
>   $

Added this:

[acme@five pahole]$ git diff
diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
index 20ee91fc911d4b39..f44c649924383a32 100644
--- a/man-pages/pahole.1
+++ b/man-pages/pahole.1
@@ -181,6 +181,14 @@ the debugging information.
 .B \-\-skip_encoding_btf_vars
 Do not encode VARs in BTF.

+.TP
+.B \-J, \-\-btf_encode
+Encode BTF information from DWARF, used in the Linux kernel build process when
+CONFIG_DEBUG_INFO_BTF=y is present, introduced in Linux v5.2. Used to implement
+features such as BPF CO-RE (Compile Once - Run Everywhere).
+
+See \fIhttp://vger.kernel.org/bpfconf2019_talks/bpf-core.pdf\fR.
+
 .TP
 .B \-\-btf_encode_force
 Ignore those symbols found invalid when encoding BTF.
[acme@five pahole]$

Re: [PATCH dwarves 4/4] btf: add support for split BTF loading and encoding

[Andrii Nakryiko]

On Wed, Nov 11, 2020 at 3:56 AM Arnaldo Carvalho de Melo
<acme@kernel.org> wrote:
>
> Em Thu, Nov 05, 2020 at 09:25:49PM -0800, Andrii Nakryiko escreveu:
> > Add support for generating split BTF, in which there is a designated base
> > BTF, containing a base set of types, and a split BTF, which extends main BTF
> > with extra types, that can reference types and strings from the main BTF.
>
> > This is going to be used to generate compact BTFs for kernel modules, with
> > vmlinux BTF being a main BTF, which all kernel modules are based off of.
>
> > These changes rely on patch set [0] to be present in libbpf submodule.
>
> >   [0] https://patchwork.kernel.org/project/netdevbpf/list/?series=377859&state=*
>
> So, applied and added this:

Awesome, thanks! Do you plan to release v1.19 soon?

>
> diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
> index 4b5e0a1bf5462b28..20ee91fc911d4b39 100644
> --- a/man-pages/pahole.1
> +++ b/man-pages/pahole.1
> @@ -185,6 +185,10 @@ Do not encode VARs in BTF.
>  .B \-\-btf_encode_force
>  Ignore those symbols found invalid when encoding BTF.
>
> +.TP
> +.B \-\-btf_base
> +Path to the base BTF file, for instance: vmlinux when encoding kernel module BTF information.
> +
>  .TP
>  .B \-l, \-\-show_first_biggest_size_base_type_member
>  Show first biggest size base_type member.
>
> ---------------
>
> The entry for btf_encode/-J is missing, I'll add in a followup patch.
>
> Also I had to fixup ARGP_btf_base to 321 as I added this, to simplify
> the kernel scripts and Makefiles:
>
>   $ pahole --numeric_version
>   118
>   $

Oh, this is nice! Can't really use it with Kbuild now due to backwards
compatibility, but maybe someday.

>
> Now to test this all by applying the kernel patches and the encoding
> module BTF, looking at it, etc.
>
> - Arnaldo
>

[...]

Re: [PATCH dwarves 4/4] btf: add support for split BTF loading and encoding

[Andrii Nakryiko]

On Wed, Nov 11, 2020 at 4:19 AM Arnaldo Carvalho de Melo
<acme@kernel.org> wrote:
>
> Em Wed, Nov 11, 2020 at 08:56:27AM -0300, Arnaldo Carvalho de Melo escreveu:
> >
> > The entry for btf_encode/-J is missing, I'll add in a followup patch.
> >
> > Also I had to fixup ARGP_btf_base to 321 as I added this, to simplify
> > the kernel scripts and Makefiles:
> >
> >   $ pahole --numeric_version
> >   118
> >   $
>
> Added this:
>
> [acme@five pahole]$ git diff
> diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
> index 20ee91fc911d4b39..f44c649924383a32 100644
> --- a/man-pages/pahole.1
> +++ b/man-pages/pahole.1
> @@ -181,6 +181,14 @@ the debugging information.
>  .B \-\-skip_encoding_btf_vars
>  Do not encode VARs in BTF.
>
> +.TP
> +.B \-J, \-\-btf_encode
> +Encode BTF information from DWARF, used in the Linux kernel build process when
> +CONFIG_DEBUG_INFO_BTF=y is present, introduced in Linux v5.2. Used to implement
> +features such as BPF CO-RE (Compile Once - Run Everywhere).
> +
> +See \fIhttp://vger.kernel.org/bpfconf2019_talks/bpf-core.pdf\fR.

Can you please point to [0] instead? That linked presentation is
already a bit out of date and will bitrot much faster. Blog post has
at least a chance at being updated with relevant important stuff. Plus
it has links both to the bpfconf2019 presentation, as well as some
other resources (including your presentation).

  [0] https://nakryiko.com/posts/bpf-portability-and-co-re/

> +
>  .TP
>  .B \-\-btf_encode_force
>  Ignore those symbols found invalid when encoding BTF.
> [acme@five pahole]$

Re: [PATCH dwarves 4/4] btf: add support for split BTF loading and encoding

[Arnaldo]

On November 11, 2020 3:29:32 PM GMT-03:00, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
>On Wed, Nov 11, 2020 at 4:19 AM Arnaldo Carvalho de Melo
><acme@kernel.org> wrote:
>>
>> Em Wed, Nov 11, 2020 at 08:56:27AM -0300, Arnaldo Carvalho de Melo
>escreveu:
>> >
>> > The entry for btf_encode/-J is missing, I'll add in a followup
>patch.
>> >
>> > Also I had to fixup ARGP_btf_base to 321 as I added this, to
>simplify
>> > the kernel scripts and Makefiles:
>> >
>> >   $ pahole --numeric_version
>> >   118
>> >   $
>>
>> Added this:
>>
>> [acme@five pahole]$ git diff
>> diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
>> index 20ee91fc911d4b39..f44c649924383a32 100644
>> --- a/man-pages/pahole.1
>> +++ b/man-pages/pahole.1
>> @@ -181,6 +181,14 @@ the debugging information.
>>  .B \-\-skip_encoding_btf_vars
>>  Do not encode VARs in BTF.
>>
>> +.TP
>> +.B \-J, \-\-btf_encode
>> +Encode BTF information from DWARF, used in the Linux kernel build
>process when
>> +CONFIG_DEBUG_INFO_BTF=y is present, introduced in Linux v5.2. Used
>to implement
>> +features such as BPF CO-RE (Compile Once - Run Everywhere).
>> +
>> +See \fIhttp://vger.kernel.org/bpfconf2019_talks/bpf-core.pdf\fR.
>
>Can you please point to [0] instead? That linked

Sure.

> presentation is
>already a bit out of date and will bitrot much faster. Blog post has
>at least a chance at being updated with relevant important stuff. Plus
>it has links both to the bpfconf2019 presentation, as well as some
>other resources (including your presentation).
>
>  [0] https://nakryiko.com/posts/bpf-portability-and-co-re/

-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

Re: [PATCH dwarves 4/4] btf: add support for split BTF loading and encoding

[Arnaldo]

On November 11, 2020 3:27:58 PM GMT-03:00, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
>On Wed, Nov 11, 2020 at 3:56 AM Arnaldo Carvalho de Melo
><acme@kernel.org> wrote:
>>
>> Em Thu, Nov 05, 2020 at 09:25:49PM -0800, Andrii Nakryiko escreveu:
>> > Add support for generating split BTF, in which there is a
>designated base
>> > BTF, containing a base set of types, and a split BTF, which extends
>main BTF
>> > with extra types, that can reference types and strings from the
>main BTF.
>>
>> > This is going to be used to generate compact BTFs for kernel
>modules, with
>> > vmlinux BTF being a main BTF, which all kernel modules are based
>off of.
>>
>> > These changes rely on patch set [0] to be present in libbpf
>submodule.
>>
>> >   [0]
>https://patchwork.kernel.org/project/netdevbpf/list/?series=377859&state=*
>>
>> So, applied and added this:
>
>Awesome, thanks! Do you plan to release v1.19 soon?

Yes

>
>>
>> diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
>> index 4b5e0a1bf5462b28..20ee91fc911d4b39 100644
>> --- a/man-pages/pahole.1
>> +++ b/man-pages/pahole.1
>> @@ -185,6 +185,10 @@ Do not encode VARs in BTF.
>>  .B \-\-btf_encode_force
>>  Ignore those symbols found invalid when encoding BTF.
>>
>> +.TP
>> +.B \-\-btf_base
>> +Path to the base BTF file, for instance: vmlinux when encoding
>kernel module BTF information.
>> +
>>  .TP
>>  .B \-l, \-\-show_first_biggest_size_base_type_member
>>  Show first biggest size base_type member.
>>
>> ---------------
>>
>> The entry for btf_encode/-J is missing, I'll add in a followup patch.
>>
>> Also I had to fixup ARGP_btf_base to 321 as I added this, to simplify
>> the kernel scripts and Makefiles:
>>
>>   $ pahole --numeric_version
>>   118
>>   $
>
>Oh, this is nice! Can't really use it with Kbuild now due to backwards
>compatibility, but maybe someday.

Well, if it fails with --numeric_version, then it is old and the warning about the minimal version being v1.19 should be emitted :)

- Arnaldo
>
>>
>> Now to test this all by applying the kernel patches and the encoding
>> module BTF, looking at it, etc.
>>
>> - Arnaldo
>>
>
>[...]

-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

Re: [PATCH dwarves 4/4] btf: add support for split BTF loading and encoding

[Andrii Nakryiko]

On Wed, Nov 11, 2020 at 10:34 AM Arnaldo <arnaldo.melo@gmail.com> wrote:
>
>
>
> On November 11, 2020 3:27:58 PM GMT-03:00, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
> >On Wed, Nov 11, 2020 at 3:56 AM Arnaldo Carvalho de Melo
> ><acme@kernel.org> wrote:
> >>
> >> Em Thu, Nov 05, 2020 at 09:25:49PM -0800, Andrii Nakryiko escreveu:
> >> > Add support for generating split BTF, in which there is a
> >designated base
> >> > BTF, containing a base set of types, and a split BTF, which extends
> >main BTF
> >> > with extra types, that can reference types and strings from the
> >main BTF.
> >>
> >> > This is going to be used to generate compact BTFs for kernel
> >modules, with
> >> > vmlinux BTF being a main BTF, which all kernel modules are based
> >off of.
> >>
> >> > These changes rely on patch set [0] to be present in libbpf
> >submodule.
> >>
> >> >   [0]
> >https://patchwork.kernel.org/project/netdevbpf/list/?series=377859&state=*
> >>
> >> So, applied and added this:
> >
> >Awesome, thanks! Do you plan to release v1.19 soon?
>
> Yes
>
> >
> >>
> >> diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
> >> index 4b5e0a1bf5462b28..20ee91fc911d4b39 100644
> >> --- a/man-pages/pahole.1
> >> +++ b/man-pages/pahole.1
> >> @@ -185,6 +185,10 @@ Do not encode VARs in BTF.
> >>  .B \-\-btf_encode_force
> >>  Ignore those symbols found invalid when encoding BTF.
> >>
> >> +.TP
> >> +.B \-\-btf_base
> >> +Path to the base BTF file, for instance: vmlinux when encoding
> >kernel module BTF information.
> >> +
> >>  .TP
> >>  .B \-l, \-\-show_first_biggest_size_base_type_member
> >>  Show first biggest size base_type member.
> >>
> >> ---------------
> >>
> >> The entry for btf_encode/-J is missing, I'll add in a followup patch.
> >>
> >> Also I had to fixup ARGP_btf_base to 321 as I added this, to simplify
> >> the kernel scripts and Makefiles:
> >>
> >>   $ pahole --numeric_version
> >>   118
> >>   $
> >
> >Oh, this is nice! Can't really use it with Kbuild now due to backwards
> >compatibility, but maybe someday.
>
> Well, if it fails with --numeric_version, then it is old and the warning about the minimal version being v1.19 should be emitted :)

Right, but for CONFIG_DEBUG_INFO_BTF v1.13 is still adequate enough
and will generates useful BTF (no functions and no module BTF, but all
the CO-RE stuff is there), I wouldn't want to force everyone to get
v1.19 immediately...

>
> - Arnaldo
> >
> >>
> >> Now to test this all by applying the kernel patches and the encoding
> >> module BTF, looking at it, etc.
> >>
> >> - Arnaldo
> >>
> >
> >[...]
>
> --
> Sent from my Android device with K-9 Mail. Please excuse my brevity.

Re: [PATCH dwarves 4/4] btf: add support for split BTF loading and encoding

[Arnaldo Carvalho de Melo]

Em Wed, Nov 11, 2020 at 10:29:32AM -0800, Andrii Nakryiko escreveu:
> On Wed, Nov 11, 2020 at 4:19 AM Arnaldo Carvalho de Melo
> <acme@kernel.org> wrote:
> >
> > Em Wed, Nov 11, 2020 at 08:56:27AM -0300, Arnaldo Carvalho de Melo escreveu:
> > >
> > > The entry for btf_encode/-J is missing, I'll add in a followup patch.
> > >
> > > Also I had to fixup ARGP_btf_base to 321 as I added this, to simplify
> > > the kernel scripts and Makefiles:
> > >
> > >   $ pahole --numeric_version
> > >   118
> > >   $
> >
> > Added this:
> >
> > [acme@five pahole]$ git diff
> > diff --git a/man-pages/pahole.1 b/man-pages/pahole.1
> > index 20ee91fc911d4b39..f44c649924383a32 100644
> > --- a/man-pages/pahole.1
> > +++ b/man-pages/pahole.1
> > @@ -181,6 +181,14 @@ the debugging information.
> >  .B \-\-skip_encoding_btf_vars
> >  Do not encode VARs in BTF.
> >
> > +.TP
> > +.B \-J, \-\-btf_encode
> > +Encode BTF information from DWARF, used in the Linux kernel build process when
> > +CONFIG_DEBUG_INFO_BTF=y is present, introduced in Linux v5.2. Used to implement
> > +features such as BPF CO-RE (Compile Once - Run Everywhere).
> > +
> > +See \fIhttp://vger.kernel.org/bpfconf2019_talks/bpf-core.pdf\fR.
> 
> Can you please point to [0] instead? That linked presentation is
> already a bit out of date and will bitrot much faster. Blog post has
> at least a chance at being updated with relevant important stuff. Plus
> it has links both to the bpfconf2019 presentation, as well as some
> other resources (including your presentation).
> 
>   [0] https://nakryiko.com/posts/bpf-portability-and-co-re/

Done, thanks for the pinter.

- Arnaldo