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From: Hao Luo <haoluo@google.com>
To: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	daniel@iogearbox.net, dwarves@vger.kernel.org, yhs@fb.com,
	Hao Luo <haoluo@google.com>
Subject: [PATCH 1/2] btf_encoder: Make encoding vars into BTF optional.
Date: Fri, 18 Sep 2020 13:40:57 -0700
Message-ID: <20200918204058.1030519-2-haoluo@google.com> (raw)
In-Reply-To: <20200918204058.1030519-1-haoluo@google.com>

Introduce an option --btf_encode_symbols to pahole so that pahole
will only encode global symbols upon request. On the kernel side,
we can add a Kconfig to turn on this feature. This would make the
rollout of pahole v1.18 safe against potential bugs in the feature
introduced in commit f3d9054ba8ff ("btf_encoder: Teach pahole to
store percpu variables in vmlinux BTF.").

Signed-off-by: Hao Luo <haoluo@google.com>
---
 btf_encoder.c |  5 ++++-
 btf_encoder.h |  2 +-
 pahole.c      | 11 ++++++++++-
 3 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/btf_encoder.c b/btf_encoder.c
index 982f59d..54ffdd1 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -237,7 +237,7 @@ 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 encode_symbols)
 {
 	bool add_index_type = false;
 	uint32_t type_id_off;
@@ -314,6 +314,9 @@ int cu__encode_btf(struct cu *cu, int verbose, bool force)
 		}
 	}
 
+	/* if there is no request to encode symbols, just finish. */
+	if (!encode_symbols)
+		goto out;
 
 	if (btfe->percpu_shndx == 0 || !btfe->symtab)
 		goto out;
diff --git a/btf_encoder.h b/btf_encoder.h
index bca2348..f2e95fe 100644
--- a/btf_encoder.h
+++ b/btf_encoder.h
@@ -13,6 +13,6 @@ 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 encode_symbols);
 
 #endif /* _BTF_ENCODER_H_ */
diff --git a/pahole.c b/pahole.c
index e1cde61..079d951 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 btf_encode_symbols;
 
 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_btf_encode_symbols	   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 = "btf_encode_symbols",
+		.key  = ARGP_btf_encode_symbols,
+		.doc  = "Encode global symbols in BTF. Off by default."
+	},
 	{
 		.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_btf_encode_symbols:
+		btf_encode_symbols = 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, btf_encode_symbols);
 		return LSK__KEEPIT;
 	}
 
-- 
2.28.0.681.g6f77f65b4e-goog


  reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-18 20:40 [PATCH 0/2] pahole: Make encoding percpu " Hao Luo
2020-09-18 20:40 ` Hao Luo [this message]
2020-09-18 21:24   ` [PATCH 1/2] btf_encoder: Make encoding " Arnaldo Carvalho de Melo
2020-09-18 21:26     ` Hao Luo
2020-09-18 21:40       ` Arnaldo Carvalho de Melo
2020-09-18 20:40 ` [PATCH 2/2] btf_encoder: Introduce option '--btf_encode_force' Hao Luo
2020-09-19  0:57 ` [PATCH 0/2] pahole: Make encoding percpu vars into BTF optional Alexei Starovoitov
2020-09-19  4:00   ` Hao Luo
2020-09-21 12:27     ` Arnaldo Carvalho de Melo

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