[v3,bpf-next,04/17] libbpf: add kind layout encoding, crc support

Commit Message

Alan Maguire Nov. 10, 2023, 11:02 a.m. UTC

Support encoding of BTF kind layout data and crcs via
btf__new_empty_opts().

Current supported opts are base_btf, add_kind_layout and
add_crc.

Kind layout information is maintained in btf.c in the
kind_layouts[] array; when BTF is created with the
add_kind_layout option it represents the current view
of supported BTF kinds.

Signed-off-by: Alan Maguire <[e-mail]>
---
 tools/lib/bpf/btf.c      | 74 ++++++++++++++++++++++++++++++++++++++--
 tools/lib/bpf/btf.h      | 11 ++++++
 tools/lib/bpf/libbpf.map |  1 +
 3 files changed, 83 insertions(+), 3 deletions(-)

Patch

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 007ce6bcad70..ed728d0511a4 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -16,6 +16,7 @@ 
 #include <linux/err.h>
 #include <linux/btf.h>
 #include <gelf.h>
+#include <zlib.h>
 #include "btf.h"
 #include "bpf.h"
 #include "libbpf.h"
@@ -28,6 +29,35 @@ 
 
 static struct btf_type btf_void;
 
+/* Describe how kinds are laid out; some have a singular element following the "struct btf_type",
+ * some have BTF_INFO_VLEN(t->info) elements.  Specify sizes for both.  Flags are currently unused.
+ * Kind layout can be optionally added to the BTF representation in a dedicated section to
+ * facilitate parsing.  New kinds must be added here.
+ */
+struct btf_kind_layout kind_layouts[NR_BTF_KINDS] = {
+/*	flags	singular element size		vlen element(s) size */
+{	0,	0,				0				}, /* _UNKN */
+{	0,	sizeof(__u32),			0				}, /* _INT */
+{	0,	0,				0				}, /* _PTR */
+{	0,	sizeof(struct btf_array),	0				}, /* _ARRAY */
+{	0,	0,				sizeof(struct btf_member)	}, /* _STRUCT */
+{	0,	0,				sizeof(struct btf_member)	}, /* _UNION */
+{	0,	0,				sizeof(struct btf_enum)		}, /* _ENUM */
+{	0,	0,				0				}, /* _FWD */
+{	0,	0,				0				}, /* _TYPEDEF */
+{	0,	0,				0				}, /* _VOLATILE */
+{	0,	0,				0				}, /* _CONST */
+{	0,	0,				0				}, /* _RESTRICT */
+{	0,	0,				0				}, /* _FUNC */
+{	0,	0,				sizeof(struct btf_param)	}, /* _FUNC_PROTO */
+{	0,	sizeof(struct btf_var),		0				}, /* _VAR */
+{	0,	0,				sizeof(struct btf_var_secinfo)	}, /* _DATASEC */
+{	0,	0,				0				}, /* _FLOAT */
+{	0,	sizeof(struct btf_decl_tag),	0				}, /* _DECL_TAG */
+{	0,	0,				0				}, /* _TYPE_TAG */
+{	0,	0,				sizeof(struct btf_enum64)	}, /* _ENUM64 */
+};
+
 struct btf {
 	/* raw BTF data in native endianness */
 	void *raw_data;
@@ -1061,8 +1091,9 @@  void btf__free(struct btf *btf)
 	free(btf);
 }
 
-static struct btf *btf_new_empty(struct btf *base_btf)
+static struct btf *btf_new_empty(struct btf_new_opts *opts)
 {
+	struct btf *base_btf = OPTS_GET(opts, base_btf, NULL);
 	struct btf_header *hdr;
 	struct btf *btf;
 
@@ -1104,6 +1135,23 @@  static struct btf *btf_new_empty(struct btf *base_btf)
 		free(btf);
 		return ERR_PTR(-ENOMEM);
 	}
+
+	if (opts->add_kind_layout) {
+		btf->kind_layout = kind_layouts;
+		hdr->kind_layout_len = sizeof(kind_layouts);
+	}
+	if (opts->add_crc) {
+		if (btf->base_btf) {
+			struct btf_header *base_hdr = btf->base_btf->hdr;
+
+			if (base_hdr->hdr_len >= sizeof(struct btf_header) &&
+			    base_hdr->flags & BTF_FLAG_CRC_SET) {
+				hdr->base_crc = base_hdr->crc;
+				hdr->flags |= BTF_FLAG_BASE_CRC_SET;
+			}
+		}
+		hdr->flags |= BTF_FLAG_CRC_SET;
+	}
 	memcpy(btf->hdr, hdr, sizeof(*hdr));
 
 	return btf;
@@ -1111,12 +1159,26 @@  static struct btf *btf_new_empty(struct btf *base_btf)
 
 struct btf *btf__new_empty(void)
 {
-	return libbpf_ptr(btf_new_empty(NULL));
+	LIBBPF_OPTS(btf_new_opts, opts);
+
+	return libbpf_ptr(btf_new_empty(&opts));
 }
 
 struct btf *btf__new_empty_split(struct btf *base_btf)
 {
-	return libbpf_ptr(btf_new_empty(base_btf));
+	LIBBPF_OPTS(btf_new_opts, opts);
+
+	opts.base_btf = base_btf;
+
+	return libbpf_ptr(btf_new_empty(&opts));
+}
+
+struct btf *btf__new_empty_opts(struct btf_new_opts *opts)
+{
+	if (!OPTS_VALID(opts, btf_new_opts))
+		return libbpf_err_ptr(-EINVAL);
+
+	return libbpf_ptr(btf_new_empty(opts));
 }
 
 static struct btf *btf_new(const void *data, __u32 size, struct btf *base_btf)
@@ -1562,6 +1624,12 @@  static void *btf_get_raw_data(const struct btf *btf, __u32 *size, bool swap_endi
 			btf_bswap_kind_layout_sec(p, hdr->kind_layout_len);
 	}
 
+	if (hdr->flags & BTF_FLAG_CRC_SET) {
+		struct btf_header *h = data;
+
+		h->crc = crc32(0L, (const Bytef *)data, data_sz);
+	}
+
 	*size = data_sz;
 	return data;
 err_out:
diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
index 8e6880d91c84..d25bd5c19eec 100644
--- a/tools/lib/bpf/btf.h
+++ b/tools/lib/bpf/btf.h
@@ -107,6 +107,17 @@  LIBBPF_API struct btf *btf__new_empty(void);
  */
 LIBBPF_API struct btf *btf__new_empty_split(struct btf *base_btf);
 
+struct btf_new_opts {
+	size_t sz;
+	struct btf *base_btf;	/* optional base BTF */
+	bool add_kind_layout;	/* add BTF kind layout information */
+	bool add_crc;		/* add CRC information */
+	size_t:0;
+};
+#define btf_new_opts__last_field add_crc
+
+LIBBPF_API struct btf *btf__new_empty_opts(struct btf_new_opts *opts);
+
 LIBBPF_API struct btf *btf__parse(const char *path, struct btf_ext **btf_ext);
 LIBBPF_API struct btf *btf__parse_split(const char *path, struct btf *base_btf);
 LIBBPF_API struct btf *btf__parse_elf(const char *path, struct btf_ext **btf_ext);
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index b52dc28dc8af..b8c0716133d1 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -401,6 +401,7 @@  LIBBPF_1.3.0 {
 		bpf_program__attach_netkit;
 		bpf_program__attach_tcx;
 		bpf_program__attach_uprobe_multi;
+		btf__new_empty_opts;
 		ring__avail_data_size;
 		ring__consume;
 		ring__consumer_pos;