[PATCH v2 0/2] pahole: Make encoding percpu vars into BTF optional.

[PATCH v2 0/2] pahole: Make encoding percpu vars into BTF optional.

[Hao Luo]

v1 -> v2:
 - Use opt-out instead of opt-in. Rename the flag name to
   '--skip_encoding_btf_vars'

Previous commit f3d9054ba8ff ("btf_encoder: Teach pahole to store
percpu variables in vmlinux BTF.") introduced a feature in btf_encoder
that encodes global symbols in BTF. However, this feature is not
protected by any flag. In order to avoid surprises after Pahole v1.18
rolls out, add a flag to toggle this feature off.

Also as a refactor, introduce '--btf_encode_force' to replace the
old '--force' and '-j' option that is used to forcefully emit BTF.

Hao Luo (2):
  btf_encoder: Allow disabling BTF var encoding.
  btf_encoder: Introduce option '--btf_encode_force'

 btf_encoder.c |  5 ++++-
 btf_encoder.h |  3 ++-
 pahole.c      | 22 +++++++++++++++++-----
 3 files changed, 23 insertions(+), 7 deletions(-)

-- 
2.28.0.681.g6f77f65b4e-goog

[PATCH v2 1/2] btf_encoder: Allow disabling BTF var encoding.

[Hao Luo]

A new feature was introduced in commit f3d9054ba8ff ("btf_encoder:
Teach pahole to store percpu variables in vmlinux BTF.") which encodes
kernel percpu variables into BTF. Add a flag --skip_encoding_btf_vars
to allow users to toggle this feature off, so that the rollout of
pahole v1.18 can be protected by potential bugs in this feature.

Signed-off-by: Hao Luo <haoluo@google.com>
---
 btf_encoder.c |  5 ++++-
 btf_encoder.h |  3 ++-
 pahole.c      | 11 ++++++++++-
 3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/btf_encoder.c b/btf_encoder.c
index 982f59d..d26c0b6 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -237,7 +237,8 @@ static struct variable *hashaddr__find_variable(const struct hlist_head hashtabl
 	return NULL;
 }
 
-int cu__encode_btf(struct cu *cu, int verbose, bool force)
+int cu__encode_btf(struct cu *cu, int verbose, bool force,
+		   bool skip_encoding_vars)
 {
 	bool add_index_type = false;
 	uint32_t type_id_off;
@@ -314,6 +315,8 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force)
 		}
 	}
 
+	if (skip_encoding_vars)
+		goto out;
 
 	if (btfe->percpu_shndx == 0 || !btfe->symtab)
 		goto out;
diff --git a/btf_encoder.h b/btf_encoder.h
index bca2348..46fb231 100644
--- a/btf_encoder.h
+++ b/btf_encoder.h
@@ -13,6 +13,7 @@ struct cu;
 
 int btf_encoder__encode();
 
-int cu__encode_btf(struct cu *cu, int verbose, bool force);
+int cu__encode_btf(struct cu *cu, int verbose, bool force,
+		   bool skip_encoding_vars);
 
 #endif /* _BTF_ENCODER_H_ */
diff --git a/pahole.c b/pahole.c
index e1cde61..4cc8d9f 100644
--- a/pahole.c
+++ b/pahole.c
@@ -26,6 +26,7 @@
 static bool btf_encode;
 static bool ctf_encode;
 static bool first_obj_only;
+static bool skip_encoding_btf_vars;
 
 static uint8_t class__include_anonymous;
 static uint8_t class__include_nested_anonymous;
@@ -809,6 +810,7 @@ ARGP_PROGRAM_VERSION_HOOK_DEF = dwarves_print_version;
 #define ARGP_header_type	   314
 #define ARGP_size_bytes		   315
 #define ARGP_range		   316
+#define ARGP_skip_encoding_btf_vars 317
 
 static const struct argp_option pahole__options[] = {
 	{
@@ -1087,6 +1089,11 @@ static const struct argp_option pahole__options[] = {
 		.key  = 'J',
 		.doc  = "Encode as BTF",
 	},
+	{
+		.name = "skip_encoding_btf_vars",
+		.key  = ARGP_skip_encoding_btf_vars,
+		.doc  = "Do not encode VARs in BTF."
+	},
 	{
 		.name = "force",
 		.key  = 'j',
@@ -1207,6 +1214,8 @@ static error_t pahole__options_parser(int key, char *arg,
 		conf.range = arg;			break;
 	case ARGP_header_type:
 		conf.header_type = arg;			break;
+	case ARGP_skip_encoding_btf_vars:
+		skip_encoding_btf_vars = true;		break;
 	default:
 		return ARGP_ERR_UNKNOWN;
 	}
@@ -2352,7 +2361,7 @@ static enum load_steal_kind pahole_stealer(struct cu *cu,
 		goto filter_it;
 
 	if (btf_encode) {
-		cu__encode_btf(cu, global_verbose, force);
+		cu__encode_btf(cu, global_verbose, force, skip_encoding_btf_vars);
 		return LSK__KEEPIT;
 	}
 
-- 
2.28.0.681.g6f77f65b4e-goog

[PATCH v2 2/2] btf_encoder: Introduce option '--btf_encode_force'

[Hao Luo]

Commit f3d9054ba8ff ("btf_encoder: Teach pahole to store percpu
variables in vmlinux BTF.") introduced an option '-j' that makes
effort in emitting VAR entries in BTF. Before no one has been using
this flag, replace the one-letter option '-j' with a full flag name
'--btf_encode_force' to save '-j' for future uses.

Signed-off-by: Hao Luo <haoluo@google.com>
---
 pahole.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/pahole.c b/pahole.c
index 4cc8d9f..ee5f2f7 100644
--- a/pahole.c
+++ b/pahole.c
@@ -27,6 +27,7 @@ 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 uint8_t class__include_anonymous;
 static uint8_t class__include_nested_anonymous;
@@ -62,7 +63,6 @@ static int show_reorg_steps;
 static const char *class_name;
 static LIST_HEAD(class_names);
 static char separator = '\t';
-static bool force;
 
 static struct conf_fprintf conf = {
 	.emit_stats = 1,
@@ -811,6 +811,7 @@ ARGP_PROGRAM_VERSION_HOOK_DEF = dwarves_print_version;
 #define ARGP_size_bytes		   315
 #define ARGP_range		   316
 #define ARGP_skip_encoding_btf_vars 317
+#define ARGP_btf_encode_force	   318
 
 static const struct argp_option pahole__options[] = {
 	{
@@ -1095,8 +1096,8 @@ static const struct argp_option pahole__options[] = {
 		.doc  = "Do not encode VARs in BTF."
 	},
 	{
-		.name = "force",
-		.key  = 'j',
+		.name = "btf_encode_force",
+		.key  = ARGP_btf_encode_force,
 		.doc  = "Ignore those symbols found invalid when encoding BTF."
 	},
 	{
@@ -1143,7 +1144,6 @@ static error_t pahole__options_parser(int key, char *arg,
 	case 'J': btf_encode = 1;
 		  conf_load.get_addr_info = true;
 		  no_bitfield_type_recode = true;	break;
-	case 'j': force = true;				break;
 	case 'l': conf.show_first_biggest_size_base_type_member = 1;	break;
 	case 'M': conf.show_only_data_members = 1;	break;
 	case 'm': stats_formatter = nr_methods_formatter; break;
@@ -1216,6 +1216,8 @@ static error_t pahole__options_parser(int key, char *arg,
 		conf.header_type = arg;			break;
 	case ARGP_skip_encoding_btf_vars:
 		skip_encoding_btf_vars = true;		break;
+	case ARGP_btf_encode_force:
+		btf_encode_force = true;		break;
 	default:
 		return ARGP_ERR_UNKNOWN;
 	}
@@ -2361,7 +2363,8 @@ static enum load_steal_kind pahole_stealer(struct cu *cu,
 		goto filter_it;
 
 	if (btf_encode) {
-		cu__encode_btf(cu, global_verbose, force, skip_encoding_btf_vars);
+		cu__encode_btf(cu, global_verbose, btf_encode_force,
+			       skip_encoding_btf_vars);
 		return LSK__KEEPIT;
 	}
 
-- 
2.28.0.681.g6f77f65b4e-goog

Re: [PATCH v2 0/2] pahole: Make encoding percpu vars into BTF optional.

[Arnaldo Carvalho de Melo]

Em Mon, Sep 21, 2020 at 12:53:08PM -0700, Hao Luo escreveu:
> v1 -> v2:
>  - Use opt-out instead of opt-in. Rename the flag name to
>    '--skip_encoding_btf_vars'
> 
> Previous commit f3d9054ba8ff ("btf_encoder: Teach pahole to store
> percpu variables in vmlinux BTF.") introduced a feature in btf_encoder
> that encodes global symbols in BTF. However, this feature is not
> protected by any flag. In order to avoid surprises after Pahole v1.18
> rolls out, add a flag to toggle this feature off.
> 
> Also as a refactor, introduce '--btf_encode_force' to replace the
> old '--force' and '-j' option that is used to forcefully emit BTF.
> 
> Hao Luo (2):
>   btf_encoder: Allow disabling BTF var encoding.
>   btf_encoder: Introduce option '--btf_encode_force'
> 
>  btf_encoder.c |  5 ++++-
>  btf_encoder.h |  3 ++-
>  pahole.c      | 22 +++++++++++++++++-----
>  3 files changed, 23 insertions(+), 7 deletions(-)
> 
> -- 
> 2.28.0.681.g6f77f65b4e-goog

You forgot to update the man page, I'll do it this time,

Thanks

- Arnaldo

Re: [PATCH v2 0/2] pahole: Make encoding percpu vars into BTF optional.

[Hao Luo]

Thanks, Arnaldo. I will remember to do it next time.

Hao

On Mon, Sep 21, 2020 at 12:56 PM Arnaldo Carvalho de Melo
<acme@kernel.org> wrote:
>
> Em Mon, Sep 21, 2020 at 12:53:08PM -0700, Hao Luo escreveu:
> > v1 -> v2:
> >  - Use opt-out instead of opt-in. Rename the flag name to
> >    '--skip_encoding_btf_vars'
> >
> > Previous commit f3d9054ba8ff ("btf_encoder: Teach pahole to store
> > percpu variables in vmlinux BTF.") introduced a feature in btf_encoder
> > that encodes global symbols in BTF. However, this feature is not
> > protected by any flag. In order to avoid surprises after Pahole v1.18
> > rolls out, add a flag to toggle this feature off.
> >
> > Also as a refactor, introduce '--btf_encode_force' to replace the
> > old '--force' and '-j' option that is used to forcefully emit BTF.
> >
> > Hao Luo (2):
> >   btf_encoder: Allow disabling BTF var encoding.
> >   btf_encoder: Introduce option '--btf_encode_force'
> >
> >  btf_encoder.c |  5 ++++-
> >  btf_encoder.h |  3 ++-
> >  pahole.c      | 22 +++++++++++++++++-----
> >  3 files changed, 23 insertions(+), 7 deletions(-)
> >
> > --
> > 2.28.0.681.g6f77f65b4e-goog
>
> You forgot to update the man page, I'll do it this time,
>
> Thanks
>
> - Arnaldo