[PATCH bpf v2 1/2] libbpf: fix deduplication of typedef with base definitions

[PATCH bpf v2 1/2] libbpf: fix deduplication of typedef with base definitions

[Antoine Tenart]

When deduplicating definitions for a module, typedef defined in the base
are not removed. This is because the hash used for base types differs
from the one used in the deduplication logic in btf_dedup_struct_type.

This was introduced by the referenced commit when moving the typedef
deduplication logic handling from btf_dedup_ref_type to
btf_dedup_struct_type, as this also changed the hash logic
(btf_hash_common to btf_hash_typedef).

This also impacts other types referencing those typedef (e.g. const). In
my test, the BTF section size of the openvswitch module went from 31KB
to 45KB.

Cc: Paul Houssel <paulhoussel2@gmail.com>
Fixes: 3781413465df ("libbpf: Fix BTF dedup to support recursive typedef definitions").
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Antoine Tenart <atenart@kernel.org>
---
 tools/lib/bpf/btf.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index ceb57b46a878..771aeaa0262b 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -4578,12 +4578,14 @@ static int btf_dedup_prep(struct btf_dedup *d)
 		case BTF_KIND_RESTRICT:
 		case BTF_KIND_PTR:
 		case BTF_KIND_FWD:
-		case BTF_KIND_TYPEDEF:
 		case BTF_KIND_FUNC:
 		case BTF_KIND_FLOAT:
 		case BTF_KIND_TYPE_TAG:
 			h = btf_hash_common(t);
 			break;
+		case BTF_KIND_TYPEDEF:
+			h = btf_hash_typedef(t);
+			break;
 		case BTF_KIND_INT:
 		case BTF_KIND_DECL_TAG:
 			h = btf_hash_int_decl_tag(t);
-- 
2.53.0

[PATCH bpf v2 2/2] selftests/bpf: ensure typedef are deduplicated in split BTF

[Antoine Tenart]

If a typedef is defined both in a base and in a split BTF, after
deduplication a single instance should be found in the base BTF.

Suggested-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Antoine Tenart <atenart@kernel.org>
---

Since v1:
- Added this patch.

 .../bpf/prog_tests/btf_dedup_split.c          | 48 ++++++++++++-------
 1 file changed, 32 insertions(+), 16 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/btf_dedup_split.c b/tools/testing/selftests/bpf/prog_tests/btf_dedup_split.c
index 5bc15bb6b7ce..0db7707ae90d 100644
--- a/tools/testing/selftests/bpf/prog_tests/btf_dedup_split.c
+++ b/tools/testing/selftests/bpf/prog_tests/btf_dedup_split.c
@@ -20,18 +20,22 @@ static void test_split_simple() {
 	btf__add_struct(btf1, "s1", 4);			/* [3] struct s1 { */
 	btf__add_field(btf1, "f1", 1, 0, 0);		/*      int f1; */
 							/* } */
+	btf__add_typedef(btf1, "t1", 1);		/* [4] typedef int */
 
 	VALIDATE_RAW_BTF(
 		btf1,
 		"[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
 		"[2] PTR '(anon)' type_id=1",
 		"[3] STRUCT 's1' size=4 vlen=1\n"
-		"\t'f1' type_id=1 bits_offset=0");
+		"\t'f1' type_id=1 bits_offset=0",
+		"[4] TYPEDEF 't1' type_id=1");
 
 	ASSERT_STREQ(btf_type_c_dump(btf1), "\
 struct s1 {\n\
 	int f1;\n\
-};\n\n", "c_dump");
+};\n\
+\n\
+typedef int t1;\n\n", "c_dump");
 
 	btf2 = btf__new_empty_split(btf1);
 	if (!ASSERT_OK_PTR(btf2, "empty_split_btf"))
@@ -49,39 +53,46 @@ struct s1 {\n\
 	ASSERT_EQ(btf_is_int(t), true, "int_kind");
 	ASSERT_STREQ(btf__str_by_offset(btf2, t->name_off), "int", "int_name");
 
-	btf__add_struct(btf2, "s2", 16);		/* [4] struct s2 {	*/
-	btf__add_field(btf2, "f1", 6, 0, 0);		/*      struct s1 f1;	*/
-	btf__add_field(btf2, "f2", 5, 32, 0);		/*      int f2;		*/
+	btf__add_struct(btf2, "s2", 16);		/* [5] struct s2 {	*/
+	btf__add_field(btf2, "f1", 7, 0, 0);		/*      struct s1 f1;	*/
+	btf__add_field(btf2, "f2", 6, 32, 0);		/*      int f2;		*/
 	btf__add_field(btf2, "f3", 2, 64, 0);		/*      int *f3;	*/
 							/* } */
 
 	/* duplicated int */
-	btf__add_int(btf2, "int", 4, BTF_INT_SIGNED);	/* [5] int */
+	btf__add_int(btf2, "int", 4, BTF_INT_SIGNED);	/* [6] int */
 
 	/* duplicated struct s1 */
-	btf__add_struct(btf2, "s1", 4);			/* [6] struct s1 { */
-	btf__add_field(btf2, "f1", 5, 0, 0);		/*      int f1; */
+	btf__add_struct(btf2, "s1", 4);			/* [7] struct s1 { */
+	btf__add_field(btf2, "f1", 6, 0, 0);		/*      int f1; */
 							/* } */
 
+	/* duplicated typedef t1 */
+	btf__add_typedef(btf2, "t1", 6);		/* [8] typedef int */
+
 	VALIDATE_RAW_BTF(
 		btf2,
 		"[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
 		"[2] PTR '(anon)' type_id=1",
 		"[3] STRUCT 's1' size=4 vlen=1\n"
 		"\t'f1' type_id=1 bits_offset=0",
-		"[4] STRUCT 's2' size=16 vlen=3\n"
-		"\t'f1' type_id=6 bits_offset=0\n"
-		"\t'f2' type_id=5 bits_offset=32\n"
+		"[4] TYPEDEF 't1' type_id=1",
+		"[5] STRUCT 's2' size=16 vlen=3\n"
+		"\t'f1' type_id=7 bits_offset=0\n"
+		"\t'f2' type_id=6 bits_offset=32\n"
 		"\t'f3' type_id=2 bits_offset=64",
-		"[5] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
-		"[6] STRUCT 's1' size=4 vlen=1\n"
-		"\t'f1' type_id=5 bits_offset=0");
+		"[6] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED",
+		"[7] STRUCT 's1' size=4 vlen=1\n"
+		"\t'f1' type_id=6 bits_offset=0",
+		"[8] TYPEDEF 't1' type_id=6");
 
 	ASSERT_STREQ(btf_type_c_dump(btf2), "\
 struct s1 {\n\
 	int f1;\n\
 };\n\
 \n\
+typedef int t1;\n\
+\n\
 struct s1___2 {\n\
 	int f1;\n\
 };\n\
@@ -90,7 +101,9 @@ struct s2 {\n\
 	struct s1___2 f1;\n\
 	int f2;\n\
 	int *f3;\n\
-};\n\n", "c_dump");
+};\n\
+\n\
+typedef int t1___2;\n\n", "c_dump");
 
 	err = btf__dedup(btf2, NULL);
 	if (!ASSERT_OK(err, "btf_dedup"))
@@ -102,7 +115,8 @@ struct s2 {\n\
 		"[2] PTR '(anon)' type_id=1",
 		"[3] STRUCT 's1' size=4 vlen=1\n"
 		"\t'f1' type_id=1 bits_offset=0",
-		"[4] STRUCT 's2' size=16 vlen=3\n"
+		"[4] TYPEDEF 't1' type_id=1",
+		"[5] STRUCT 's2' size=16 vlen=3\n"
 		"\t'f1' type_id=3 bits_offset=0\n"
 		"\t'f2' type_id=1 bits_offset=32\n"
 		"\t'f3' type_id=2 bits_offset=64");
@@ -112,6 +126,8 @@ struct s1 {\n\
 	int f1;\n\
 };\n\
 \n\
+typedef int t1;\n\
+\n\
 struct s2 {\n\
 	struct s1 f1;\n\
 	int f2;\n\
-- 
2.53.0

Re: [PATCH bpf v2 1/2] libbpf: fix deduplication of typedef with base definitions

[Alan Maguire]

On 17/04/2026 09:33, Antoine Tenart wrote:
> When deduplicating definitions for a module, typedef defined in the base
> are not removed. This is because the hash used for base types differs
> from the one used in the deduplication logic in btf_dedup_struct_type.
> 
> This was introduced by the referenced commit when moving the typedef
> deduplication logic handling from btf_dedup_ref_type to
> btf_dedup_struct_type, as this also changed the hash logic
> (btf_hash_common to btf_hash_typedef).
> 
> This also impacts other types referencing those typedef (e.g. const). In
> my test, the BTF section size of the openvswitch module went from 31KB
> to 45KB.
> 
> Cc: Paul Houssel <paulhoussel2@gmail.com>
> Fixes: 3781413465df ("libbpf: Fix BTF dedup to support recursive typedef definitions").
> Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
> Signed-off-by: Antoine Tenart <atenart@kernel.org>

Thanks; verified that this patch resolves issues with duplicated typedefs
in modules. Selftest in patch 2 fails prior to this patch, and succeeds after 
it is applied. So for the series

Tested-by: Alan Maguire <alan.maguire@oracle.com>

> ---
>  tools/lib/bpf/btf.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index ceb57b46a878..771aeaa0262b 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -4578,12 +4578,14 @@ static int btf_dedup_prep(struct btf_dedup *d)
>  		case BTF_KIND_RESTRICT:
>  		case BTF_KIND_PTR:
>  		case BTF_KIND_FWD:
> -		case BTF_KIND_TYPEDEF:
>  		case BTF_KIND_FUNC:
>  		case BTF_KIND_FLOAT:
>  		case BTF_KIND_TYPE_TAG:
>  			h = btf_hash_common(t);
>  			break;
> +		case BTF_KIND_TYPEDEF:
> +			h = btf_hash_typedef(t);
> +			break;
>  		case BTF_KIND_INT:
>  		case BTF_KIND_DECL_TAG:
>  			h = btf_hash_int_decl_tag(t);