Commit 4cedc0da authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
Browse files

libbpf: add .BTF.ext offset relocation section loading 



Add support for BPF CO-RE offset relocations. Add section/record
iteration macros for .BTF.ext. These macro are useful for iterating over
each .BTF.ext record, either for dumping out contents or later for BPF
CO-RE relocation handling.

To enable other parts of libbpf to work with .BTF.ext contents, moved
a bunch of type definitions into libbpf_internal.h.

Signed-off-by: default avatarAndrii Nakryiko <andriin@fb.com>
Acked-by: default avatarSong Liu <songliubraving@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent b03bc685

tools/lib/bpf/btf.c

+27 −42
Original line number Diff line number Diff line
@@ -35,47 +35,6 @@ struct btf { 
	int fd;

};



struct btf_ext_info {

	/*

	 * info points to the individual info section (e.g. func_info and

	 * line_info) from the .BTF.ext. It does not include the __u32 rec_size.

	 */

	void *info;

	__u32 rec_size;

	__u32 len;

};



struct btf_ext {

	union {

		struct btf_ext_header *hdr;

		void *data;

	};

	struct btf_ext_info func_info;

	struct btf_ext_info line_info;

	__u32 data_size;

};



struct btf_ext_info_sec {

	__u32	sec_name_off;

	__u32	num_info;

	/* Followed by num_info * record_size number of bytes */

	__u8	data[0];

};



/* The minimum bpf_func_info checked by the loader */

struct bpf_func_info_min {

	__u32   insn_off;

	__u32   type_id;

};



/* The minimum bpf_line_info checked by the loader */

struct bpf_line_info_min {

	__u32	insn_off;

	__u32	file_name_off;

	__u32	line_off;

	__u32	line_col;

};



static inline __u64 ptr_to_u64(const void *ptr)

{

	return (__u64) (unsigned long) ptr;
@@ -822,6 +781,9 @@ static int btf_ext_setup_info(struct btf_ext *btf_ext, 
	/* The start of the info sec (including the __u32 record_size). */

	void *info;



	if (ext_sec->len == 0)

		return 0;



	if (ext_sec->off & 0x03) {

		pr_debug(".BTF.ext %s section is not aligned to 4 bytes\n",

		     ext_sec->desc);
@@ -925,11 +887,24 @@ static int btf_ext_setup_line_info(struct btf_ext *btf_ext) 
	return btf_ext_setup_info(btf_ext, &param);

}



static int btf_ext_setup_offset_reloc(struct btf_ext *btf_ext)

{

	struct btf_ext_sec_setup_param param = {

		.off = btf_ext->hdr->offset_reloc_off,

		.len = btf_ext->hdr->offset_reloc_len,

		.min_rec_size = sizeof(struct bpf_offset_reloc),

		.ext_info = &btf_ext->offset_reloc_info,

		.desc = "offset_reloc",

	};



	return btf_ext_setup_info(btf_ext, &param);

}



static int btf_ext_parse_hdr(__u8 *data, __u32 data_size)

{

	const struct btf_ext_header *hdr = (struct btf_ext_header *)data;



	if (data_size < offsetof(struct btf_ext_header, func_info_off) ||

	if (data_size < offsetofend(struct btf_ext_header, hdr_len) ||

	    data_size < hdr->hdr_len) {

		pr_debug("BTF.ext header not found");

		return -EINVAL;
@@ -987,6 +962,9 @@ struct btf_ext *btf_ext__new(__u8 *data, __u32 size) 
	}

	memcpy(btf_ext->data, data, size);



	if (btf_ext->hdr->hdr_len <

	    offsetofend(struct btf_ext_header, line_info_len))

		goto done;

	err = btf_ext_setup_func_info(btf_ext);

	if (err)

		goto done;
@@ -995,6 +973,13 @@ struct btf_ext *btf_ext__new(__u8 *data, __u32 size) 
	if (err)

		goto done;



	if (btf_ext->hdr->hdr_len <

	    offsetofend(struct btf_ext_header, offset_reloc_len))

		goto done;

	err = btf_ext_setup_offset_reloc(btf_ext);

	if (err)

		goto done;



done:

	if (err) {

		btf_ext__free(btf_ext);

tools/lib/bpf/btf.h

+4 −0
Original line number Diff line number Diff line
@@ -58,6 +58,10 @@ struct btf_ext_header { 
	__u32	func_info_len;

	__u32	line_info_off;

	__u32	line_info_len;



	/* optional part of .BTF.ext header */

	__u32	offset_reloc_off;

	__u32	offset_reloc_len;

};



LIBBPF_API void btf__free(struct btf *btf);

tools/lib/bpf/libbpf_internal.h

+105 −0
Original line number Diff line number Diff line
@@ -29,6 +29,10 @@ 
#ifndef max

# define max(x, y) ((x) < (y) ? (y) : (x))

#endif

#ifndef offsetofend

# define offsetofend(TYPE, FIELD) \

	(offsetof(TYPE, FIELD) + sizeof(((TYPE *)0)->FIELD))

#endif



extern void libbpf_print(enum libbpf_print_level level,

			 const char *format, ...)
@@ -46,4 +50,105 @@ do { \ 
int libbpf__load_raw_btf(const char *raw_types, size_t types_len,

			 const char *str_sec, size_t str_len);



struct btf_ext_info {

	/*

	 * info points to the individual info section (e.g. func_info and

	 * line_info) from the .BTF.ext. It does not include the __u32 rec_size.

	 */

	void *info;

	__u32 rec_size;

	__u32 len;

};



#define for_each_btf_ext_sec(seg, sec)					\

	for (sec = (seg)->info;						\

	     (void *)sec < (seg)->info + (seg)->len;			\

	     sec = (void *)sec + sizeof(struct btf_ext_info_sec) +	\

		   (seg)->rec_size * sec->num_info)



#define for_each_btf_ext_rec(seg, sec, i, rec)				\

	for (i = 0, rec = (void *)&(sec)->data;				\

	     i < (sec)->num_info;					\

	     i++, rec = (void *)rec + (seg)->rec_size)



struct btf_ext {

	union {

		struct btf_ext_header *hdr;

		void *data;

	};

	struct btf_ext_info func_info;

	struct btf_ext_info line_info;

	struct btf_ext_info offset_reloc_info;

	__u32 data_size;

};



struct btf_ext_info_sec {

	__u32	sec_name_off;

	__u32	num_info;

	/* Followed by num_info * record_size number of bytes */

	__u8	data[0];

};



/* The minimum bpf_func_info checked by the loader */

struct bpf_func_info_min {

	__u32   insn_off;

	__u32   type_id;

};



/* The minimum bpf_line_info checked by the loader */

struct bpf_line_info_min {

	__u32	insn_off;

	__u32	file_name_off;

	__u32	line_off;

	__u32	line_col;

};



/* The minimum bpf_offset_reloc checked by the loader

 *

 * Offset relocation captures the following data:

 * - insn_off - instruction offset (in bytes) within a BPF program that needs

 *   its insn->imm field to be relocated with actual offset;

 * - type_id - BTF type ID of the "root" (containing) entity of a relocatable

 *   offset;

 * - access_str_off - offset into corresponding .BTF string section. String

 *   itself encodes an accessed field using a sequence of field and array

 *   indicies, separated by colon (:). It's conceptually very close to LLVM's

 *   getelementptr ([0]) instruction's arguments for identifying offset to 

 *   a field.

 *

 * Example to provide a better feel.

 *

 *   struct sample {

 *       int a;

 *       struct {

 *           int b[10];

 *       };

 *   };

 *

 *   struct sample *s = ...;

 *   int x = &s->a;     // encoded as "0:0" (a is field #0)

 *   int y = &s->b[5];  // encoded as "0:1:0:5" (anon struct is field #1, 

 *                      // b is field #0 inside anon struct, accessing elem #5)

 *   int z = &s[10]->b; // encoded as "10:1" (ptr is used as an array)

 *

 * type_id for all relocs in this example  will capture BTF type id of

 * `struct sample`.

 *

 * Such relocation is emitted when using __builtin_preserve_access_index()

 * Clang built-in, passing expression that captures field address, e.g.:

 *

 * bpf_probe_read(&dst, sizeof(dst),

 *		  __builtin_preserve_access_index(&src->a.b.c));

 *

 * In this case Clang will emit offset relocation recording necessary data to

 * be able to find offset of embedded `a.b.c` field within `src` struct.

 *

 *   [0] https://llvm.org/docs/LangRef.html#getelementptr-instruction

 */

struct bpf_offset_reloc {

	__u32   insn_off;

	__u32   type_id;

	__u32   access_str_off;

};



#endif /* __LIBBPF_LIBBPF_INTERNAL_H */

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