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[v3,bpf-next,01/17] btf: add kind layout encoding, crcs to UAPI

Message ID 20231110110304.63910-2-alan.maguire@oracle.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series Add kind layout, CRCs to BTF | expand

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Commit Message

Alan Maguire Nov. 10, 2023, 11:02 a.m. UTC 
BTF kind layouts provide information to parse BTF kinds.
By separating parsing BTF from using all the information
it provides, we allow BTF to encode new features even if
they cannot be used.  This is helpful in particular for
cases where newer tools for BTF generation run on an
older kernel; BTF kinds may be present that the kernel
cannot yet use, but at least it can parse the BTF
provided.  Meanwhile userspace tools with newer libbpf
may be able to use the newer information.

The intent is to support encoding of kind layouts
optionally so that tools like pahole can add this
information.  So for each kind we record

- kind-related flags
- length of singular element following struct btf_type
- length of each of the btf_vlen() elements following

In addition we make space in the BTF header for
CRC32s computed over the BTF along with a CRC for
the base BTF; this allows split BTF to identify
a mismatch explicitly.

The ideas here were discussed at [1], [2]; hence

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>

[1] https://lore.kernel.org/bpf/CAEf4BzYjWHRdNNw4B=eOXOs_ONrDwrgX4bn=Nuc1g8JPFC34MA@mail.gmail.com/
[2] https://lore.kernel.org/bpf/20230531201936.1992188-1-alan.maguire@oracle.com/
---
 include/uapi/linux/btf.h       | 18 ++++++++++++++++++
 tools/include/uapi/linux/btf.h | 18 ++++++++++++++++++
 2 files changed, 36 insertions(+)
diff mbox series

Patch

diff --git a/include/uapi/linux/btf.h b/include/uapi/linux/btf.h
index ec1798b6d3ff..f4965de18f0c 100644
--- a/include/uapi/linux/btf.h
+++ b/include/uapi/linux/btf.h
@@ -8,6 +8,19 @@ 
 #define BTF_MAGIC	0xeB9F
 #define BTF_VERSION	1
 
+/* kind layout section consists of a struct btf_kind_layout for each known
+ * kind at BTF encoding time.
+ */
+struct btf_kind_layout {
+	__u16 flags;		/* see BTF_KIND_LAYOUT_* values above */
+	__u8 info_sz;		/* size of singular element after btf_type */
+	__u8 elem_sz;		/* size of each of btf_vlen(t) elements */
+};
+
+/* for CRCs for BTF, base BTF to be considered usable, flags must be set. */
+#define BTF_FLAG_CRC_SET		(1 << 0)
+#define BTF_FLAG_BASE_CRC_SET		(1 << 1)
+
 struct btf_header {
 	__u16	magic;
 	__u8	version;
@@ -19,6 +32,11 @@  struct btf_header {
 	__u32	type_len;	/* length of type section	*/
 	__u32	str_off;	/* offset of string section	*/
 	__u32	str_len;	/* length of string section	*/
+	__u32	kind_layout_off;/* offset of kind layout section */
+	__u32	kind_layout_len;/* length of kind layout section */
+
+	__u32	crc;		/* crc of BTF; used if flags set BTF_FLAG_CRC_SET */
+	__u32	base_crc;	/* crc of base BTF; used if flags set BTF_FLAG_BASE_CRC_SET */
 };
 
 /* Max # of type identifier */
diff --git a/tools/include/uapi/linux/btf.h b/tools/include/uapi/linux/btf.h
index ec1798b6d3ff..f4965de18f0c 100644
--- a/tools/include/uapi/linux/btf.h
+++ b/tools/include/uapi/linux/btf.h
@@ -8,6 +8,19 @@ 
 #define BTF_MAGIC	0xeB9F
 #define BTF_VERSION	1
 
+/* kind layout section consists of a struct btf_kind_layout for each known
+ * kind at BTF encoding time.
+ */
+struct btf_kind_layout {
+	__u16 flags;		/* see BTF_KIND_LAYOUT_* values above */
+	__u8 info_sz;		/* size of singular element after btf_type */
+	__u8 elem_sz;		/* size of each of btf_vlen(t) elements */
+};
+
+/* for CRCs for BTF, base BTF to be considered usable, flags must be set. */
+#define BTF_FLAG_CRC_SET		(1 << 0)
+#define BTF_FLAG_BASE_CRC_SET		(1 << 1)
+
 struct btf_header {
 	__u16	magic;
 	__u8	version;
@@ -19,6 +32,11 @@  struct btf_header {
 	__u32	type_len;	/* length of type section	*/
 	__u32	str_off;	/* offset of string section	*/
 	__u32	str_len;	/* length of string section	*/
+	__u32	kind_layout_off;/* offset of kind layout section */
+	__u32	kind_layout_len;/* length of kind layout section */
+
+	__u32	crc;		/* crc of BTF; used if flags set BTF_FLAG_CRC_SET */
+	__u32	base_crc;	/* crc of base BTF; used if flags set BTF_FLAG_BASE_CRC_SET */
 };
 
 /* Max # of type identifier */