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

[Hao Luo <haoluo@xxxxxxxxxx>]

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@xxxxxxxxxx>
---
 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