Merge branch 'libbpf: support loading/storing any BTF'

Andrii Nakryiko says:

====================
Add support for loading and storing BTF in either little- or big-endian
integer encodings, regardless of host endianness. This allows users of libbpf
to not care about endianness when they don't want to and transparently
open/load BTF of any endianness. libbpf will preserve original endianness and
will convert output raw data as necessary back to original endianness, if
necessary. This allows tools like pahole to be ignorant to such issues during
cross-compilation.

While working with BTF data in memory, the endianness is always native to the
host. Convetion can happen only during btf__get_raw_data() call, and only in
a raw data copy.

Additionally, it's possible to force output BTF endianness through new
btf__set_endianness() API. This which allows to create flexible tools doing
arbitrary conversions of BTF endianness, just by relying on libbpf.

Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Cc: Tony Ambardar <tony.ambardar@gmail.com>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Luka Perkov <luka.perkov@sartura.hr>
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 246 insertions, 64 deletions

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index c25f49fad5a6..e1dbd766c698 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
 /* Copyright (c) 2018 Facebook */
 
+#include <byteswap.h>
 #include <endian.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -27,8 +28,13 @@
 static struct btf_type btf_void;
 
 struct btf {
+	/* raw BTF data in native endianness */
 	void *raw_data;
+	/* raw BTF data in non-native endianness */
+	void *raw_data_swapped;
 	__u32 raw_size;
+	/* whether target endianness differs from the native one */
+	bool swapped_endian;
 
 	/*
 	 * When BTF is loaded from an ELF or raw memory it is stored
@@ -153,9 +159,19 @@ static int btf_add_type_idx_entry(struct btf *btf, __u32 type_off)
 	return 0;
 }
 
+static void btf_bswap_hdr(struct btf_header *h)
+{
+	h->magic = bswap_16(h->magic);
+	h->hdr_len = bswap_32(h->hdr_len);
+	h->type_off = bswap_32(h->type_off);
+	h->type_len = bswap_32(h->type_len);
+	h->str_off = bswap_32(h->str_off);
+	h->str_len = bswap_32(h->str_len);
+}
+
 static int btf_parse_hdr(struct btf *btf)
 {
-	const struct btf_header *hdr = btf->hdr;
+	struct btf_header *hdr = btf->hdr;
 	__u32 meta_left;
 
 	if (btf->raw_size < sizeof(struct btf_header)) {
@@ -163,21 +179,19 @@ static int btf_parse_hdr(struct btf *btf)
 		return -EINVAL;
 	}
 
-	if (hdr->magic != BTF_MAGIC) {
+	if (hdr->magic == bswap_16(BTF_MAGIC)) {
+		btf->swapped_endian = true;
+		if (bswap_32(hdr->hdr_len) != sizeof(struct btf_header)) {
+			pr_warn("Can't load BTF with non-native endianness due to unsupported header length %u\n",
+				bswap_32(hdr->hdr_len));
+			return -ENOTSUP;
+		}
+		btf_bswap_hdr(hdr);
+	} else if (hdr->magic != BTF_MAGIC) {
 		pr_debug("Invalid BTF magic:%x\n", hdr->magic);
 		return -EINVAL;
 	}
 
-	if (hdr->version != BTF_VERSION) {
-		pr_debug("Unsupported BTF version:%u\n", hdr->version);
-		return -ENOTSUP;
-	}
-
-	if (hdr->flags) {
-		pr_debug("Unsupported BTF flags:%x\n", hdr->flags);
-		return -ENOTSUP;
-	}
-
 	meta_left = btf->raw_size - sizeof(*hdr);
 	if (!meta_left) {
 		pr_debug("BTF has no data\n");
@@ -224,7 +238,7 @@ static int btf_parse_str_sec(struct btf *btf)
 
 static int btf_type_size(const struct btf_type *t)
 {
-	int base_size = sizeof(struct btf_type);
+	const int base_size = sizeof(struct btf_type);
 	__u16 vlen = btf_vlen(t);
 
 	switch (btf_kind(t)) {
@@ -257,12 +271,83 @@ static int btf_type_size(const struct btf_type *t)
 	}
 }
 
+static void btf_bswap_type_base(struct btf_type *t)
+{
+	t->name_off = bswap_32(t->name_off);
+	t->info = bswap_32(t->info);
+	t->type = bswap_32(t->type);
+}
+
+static int btf_bswap_type_rest(struct btf_type *t)
+{
+	struct btf_var_secinfo *v;
+	struct btf_member *m;
+	struct btf_array *a;
+	struct btf_param *p;
+	struct btf_enum *e;
+	__u16 vlen = btf_vlen(t);
+	int i;
+
+	switch (btf_kind(t)) {
+	case BTF_KIND_FWD:
+	case BTF_KIND_CONST:
+	case BTF_KIND_VOLATILE:
+	case BTF_KIND_RESTRICT:
+	case BTF_KIND_PTR:
+	case BTF_KIND_TYPEDEF:
+	case BTF_KIND_FUNC:
+		return 0;
+	case BTF_KIND_INT:
+		*(__u32 *)(t + 1) = bswap_32(*(__u32 *)(t + 1));
+		return 0;
+	case BTF_KIND_ENUM:
+		for (i = 0, e = btf_enum(t); i < vlen; i++, e++) {
+			e->name_off = bswap_32(e->name_off);
+			e->val = bswap_32(e->val);
+		}
+		return 0;
+	case BTF_KIND_ARRAY:
+		a = btf_array(t);
+		a->type = bswap_32(a->type);
+		a->index_type = bswap_32(a->index_type);
+		a->nelems = bswap_32(a->nelems);
+		return 0;
+	case BTF_KIND_STRUCT:
+	case BTF_KIND_UNION:
+		for (i = 0, m = btf_members(t); i < vlen; i++, m++) {
+			m->name_off = bswap_32(m->name_off);
+			m->type = bswap_32(m->type);
+			m->offset = bswap_32(m->offset);
+		}
+		return 0;
+	case BTF_KIND_FUNC_PROTO:
+		for (i = 0, p = btf_params(t); i < vlen; i++, p++) {
+			p->name_off = bswap_32(p->name_off);
+			p->type = bswap_32(p->type);
+		}
+		return 0;
+	case BTF_KIND_VAR:
+		btf_var(t)->linkage = bswap_32(btf_var(t)->linkage);
+		return 0;
+	case BTF_KIND_DATASEC:
+		for (i = 0, v = btf_var_secinfos(t); i < vlen; i++, v++) {
+			v->type = bswap_32(v->type);
+			v->offset = bswap_32(v->offset);
+			v->size = bswap_32(v->size);
+		}
+		return 0;
+	default:
+		pr_debug("Unsupported BTF_KIND:%u\n", btf_kind(t));
+		return -EINVAL;
+	}
+}
+
 static int btf_parse_type_sec(struct btf *btf)
 {
 	struct btf_header *hdr = btf->hdr;
 	void *next_type = btf->types_data;
 	void *end_type = next_type + hdr->type_len;
-	int err, type_size;
+	int err, i, type_size;
 
 	/* VOID (type_id == 0) is specially handled by btf__get_type_by_id(),
 	 * so ensure we can never properly use its offset from index by
@@ -272,19 +357,36 @@ static int btf_parse_type_sec(struct btf *btf)
 	if (err)
 		return err;
 
-	while (next_type < end_type) {
-		err = btf_add_type_idx_entry(btf, next_type - btf->types_data);
-		if (err)
-			return err;
+	while (next_type + sizeof(struct btf_type) <= end_type) {
+		i++;
+
+		if (btf->swapped_endian)
+			btf_bswap_type_base(next_type);
 
 		type_size = btf_type_size(next_type);
 		if (type_size < 0)
 			return type_size;
+		if (next_type + type_size > end_type) {
+			pr_warn("BTF type [%d] is malformed\n", i);
+			return -EINVAL;
+		}
+
+		if (btf->swapped_endian && btf_bswap_type_rest(next_type))
+			return -EINVAL;
+
+		err = btf_add_type_idx_entry(btf, next_type - btf->types_data);
+		if (err)
+			return err;
 
 		next_type += type_size;
 		btf->nr_types++;
 	}
 
+	if (next_type != end_type) {
+		pr_warn("BTF types data is malformed\n");
+		return -EINVAL;
+	}
+
 	return 0;
 }
 
@@ -373,6 +475,38 @@ int btf__set_pointer_size(struct btf *btf, size_t ptr_sz)
 	return 0;
 }
 
+static bool is_host_big_endian(void)
+{
+#if __BYTE_ORDER == __LITTLE_ENDIAN
+	return false;
+#elif __BYTE_ORDER == __BIG_ENDIAN
+	return true;
+#else
+# error "Unrecognized __BYTE_ORDER__"
+#endif
+}
+
+enum btf_endianness btf__endianness(const struct btf *btf)
+{
+	if (is_host_big_endian())
+		return btf->swapped_endian ? BTF_LITTLE_ENDIAN : BTF_BIG_ENDIAN;
+	else
+		return btf->swapped_endian ? BTF_BIG_ENDIAN : BTF_LITTLE_ENDIAN;
+}
+
+int btf__set_endianness(struct btf *btf, enum btf_endianness endian)
+{
+	if (endian != BTF_LITTLE_ENDIAN && endian != BTF_BIG_ENDIAN)
+		return -EINVAL;
+
+	btf->swapped_endian = is_host_big_endian() != (endian == BTF_BIG_ENDIAN);
+	if (!btf->swapped_endian) {
+		free(btf->raw_data_swapped);
+		btf->raw_data_swapped = NULL;
+	}
+	return 0;
+}
+
 static bool btf_type_is_void(const struct btf_type *t)
 {
 	return t == &btf_void || btf_is_fwd(t);
@@ -561,6 +695,7 @@ void btf__free(struct btf *btf)
 		free(btf->strs_data);
 	}
 	free(btf->raw_data);
+	free(btf->raw_data_swapped);
 	free(btf->type_offs);
 	free(btf);
 }
@@ -572,8 +707,10 @@ struct btf *btf__new_empty(void)
 	btf = calloc(1, sizeof(*btf));
 	if (!btf)
 		return ERR_PTR(-ENOMEM);
+
 	btf->fd = -1;
 	btf->ptr_sz = sizeof(void *);
+	btf->swapped_endian = false;
 
 	/* +1 for empty string at offset 0 */
 	btf->raw_size = sizeof(struct btf_header) + 1;
@@ -604,8 +741,6 @@ struct btf *btf__new(const void *data, __u32 size)
 	if (!btf)
 		return ERR_PTR(-ENOMEM);
 
-	btf->fd = -1;
-
 	btf->raw_data = malloc(size);
 	if (!btf->raw_data) {
 		err = -ENOMEM;
@@ -624,6 +759,10 @@ struct btf *btf__new(const void *data, __u32 size)
 
 	err = btf_parse_str_sec(btf);
 	err = err ?: btf_parse_type_sec(btf);
+	if (err)
+		goto done;
+
+	btf->fd = -1;
 
 done:
 	if (err) {
@@ -634,17 +773,6 @@ done:
 	return btf;
 }
 
-static bool btf_check_endianness(const GElf_Ehdr *ehdr)
-{
-#if __BYTE_ORDER == __LITTLE_ENDIAN
-	return ehdr->e_ident[EI_DATA] == ELFDATA2LSB;
-#elif __BYTE_ORDER == __BIG_ENDIAN
-	return ehdr->e_ident[EI_DATA] == ELFDATA2MSB;
-#else
-# error "Unrecognized __BYTE_ORDER__"
-#endif
-}
-
 struct btf *btf__parse_elf(const char *path, struct btf_ext **btf_ext)
 {
 	Elf_Data *btf_data = NULL, *btf_ext_data = NULL;
@@ -677,10 +805,6 @@ struct btf *btf__parse_elf(const char *path, struct btf_ext **btf_ext)
 		pr_warn("failed to get EHDR from %s\n", path);
 		goto done;
 	}
-	if (!btf_check_endianness(&ehdr)) {
-		pr_warn("non-native ELF endianness is not supported\n");
-		goto done;
-	}
 	if (!elf_rawdata(elf_getscn(elf, ehdr.e_shstrndx), NULL)) {
 		pr_warn("failed to get e_shstrndx from %s\n", path);
 		goto done;
@@ -792,7 +916,7 @@ struct btf *btf__parse_raw(const char *path)
 		err = -EIO;
 		goto err_out;
 	}
-	if (magic != BTF_MAGIC) {
+	if (magic != BTF_MAGIC && magic != bswap_16(BTF_MAGIC)) {
 		/* definitely not a raw BTF */
 		err = -EPROTO;
 		goto err_out;
@@ -942,11 +1066,13 @@ int btf__finalize_data(struct bpf_object *obj, struct btf *btf)
 	return err;
 }
 
+static void *btf_get_raw_data(const struct btf *btf, __u32 *size, bool swap_endian);
+
 int btf__load(struct btf *btf)
 {
 	__u32 log_buf_size = 0, raw_size;
 	char *log_buf = NULL;
-	const void *raw_data;
+	void *raw_data;
 	int err = 0;
 
 	if (btf->fd >= 0)
@@ -961,11 +1087,14 @@ retry_load:
 		*log_buf = 0;
 	}
 
-	raw_data = btf__get_raw_data(btf, &raw_size);
+	raw_data = btf_get_raw_data(btf, &raw_size, false);
 	if (!raw_data) {
 		err = -ENOMEM;
 		goto done;
 	}
+	/* cache native raw data representation */
+	btf->raw_size = raw_size;
+	btf->raw_data = raw_data;
 
 	btf->fd = bpf_load_btf(raw_data, raw_size, log_buf, log_buf_size, false);
 	if (btf->fd < 0) {
@@ -998,31 +1127,73 @@ void btf__set_fd(struct btf *btf, int fd)
 	btf->fd = fd;
 }
 
-const void *btf__get_raw_data(const struct btf *btf_ro, __u32 *size)
+static void *btf_get_raw_data(const struct btf *btf, __u32 *size, bool swap_endian)
 {
-	struct btf *btf = (struct btf *)btf_ro;
+	struct btf_header *hdr = btf->hdr;
+	struct btf_type *t;
+	void *data, *p;
+	__u32 data_sz;
+	int i;
 
-	if (!btf->raw_data) {
-		struct btf_header *hdr = btf->hdr;
-		void *data;
+	data = swap_endian ? btf->raw_data_swapped : btf->raw_data;
+	if (data) {
+		*size = btf->raw_size;
+		return data;
+	}
+
+	data_sz = hdr->hdr_len + hdr->type_len + hdr->str_len;
+	data = calloc(1, data_sz);
+	if (!data)
+		return NULL;
+	p = data;
+
+	memcpy(p, hdr, hdr->hdr_len);
+	if (swap_endian)
+		btf_bswap_hdr(p);
+	p += hdr->hdr_len;
+
+	memcpy(p, btf->types_data, hdr->type_len);
+	if (swap_endian) {
+		for (i = 1; i <= btf->nr_types; i++) {
+			t = p  + btf->type_offs[i];
+			/* btf_bswap_type_rest() relies on native t->info, so
+			 * we swap base type info after we swapped all the
+			 * additional information
+			 */
+			if (btf_bswap_type_rest(t))
+				goto err_out;
+			btf_bswap_type_base(t);
+		}
+	}
+	p += hdr->type_len;
+
+	memcpy(p, btf->strs_data, hdr->str_len);
+	p += hdr->str_len;
 
-		btf->raw_size = hdr->hdr_len + hdr->type_len + hdr->str_len;
-		btf->raw_data = calloc(1, btf->raw_size);
-		if (!btf->raw_data)
-			return NULL;
-		data = btf->raw_data;
+	*size = data_sz;
+	return data;
+err_out:
+	free(data);
+	return NULL;
+}
 
-		memcpy(data, hdr, hdr->hdr_len);
-		data += hdr->hdr_len;
+const void *btf__get_raw_data(const struct btf *btf_ro, __u32 *size)
+{
+	struct btf *btf = (struct btf *)btf_ro;
+	__u32 data_sz;
+	void *data;
 
-		memcpy(data, btf->types_data, hdr->type_len);
-		data += hdr->type_len;
+	data = btf_get_raw_data(btf, &data_sz, btf->swapped_endian);
+	if (!data)
+		return NULL;
 
-		memcpy(data, btf->strs_data, hdr->str_len);
-		data += hdr->str_len;
-	}
-	*size = btf->raw_size;
-	return btf->raw_data;
+	btf->raw_size = data_sz;
+	if (btf->swapped_endian)
+		btf->raw_data_swapped = data;
+	else
+		btf->raw_data = data;
+	*size = data_sz;
+	return data;
 }
 
 const char *btf__str_by_offset(const struct btf *btf, __u32 offset)
@@ -1190,6 +1361,18 @@ static bool strs_hash_equal_fn(const void *key1, const void *key2, void *ctx)
 	return strcmp(str1, str2) == 0;
 }
 
+static void btf_invalidate_raw_data(struct btf *btf)
+{
+	if (btf->raw_data) {
+		free(btf->raw_data);
+		btf->raw_data = NULL;
+	}
+	if (btf->raw_data_swapped) {
+		free(btf->raw_data_swapped);
+		btf->raw_data_swapped = NULL;
+	}
+}
+
 /* Ensure BTF is ready to be modified (by splitting into a three memory
  * regions for header, types, and strings). Also invalidate cached
  * raw_data, if any.
@@ -1203,10 +1386,7 @@ static int btf_ensure_modifiable(struct btf *btf)
 
 	if (btf_is_modifiable(btf)) {
 		/* any BTF modification invalidates raw_data */
-		if (btf->raw_data) {
-			free(btf->raw_data);
-			btf->raw_data = NULL;
-		}
+		btf_invalidate_raw_data(btf);
 		return 0;
 	}
 
@@ -1254,8 +1434,7 @@ static int btf_ensure_modifiable(struct btf *btf)
 	btf->strs_deduped = btf->hdr->str_len <= 1;
 
 	/* invalidate raw_data representation */
-	free(btf->raw_data);
-	btf->raw_data = NULL;
+	btf_invalidate_raw_data(btf);
 
 	return 0;
 
@@ -2275,7 +2454,10 @@ static int btf_ext_parse_hdr(__u8 *data, __u32 data_size)
 		return -EINVAL;
 	}
 
-	if (hdr->magic != BTF_MAGIC) {
+	if (hdr->magic == bswap_16(BTF_MAGIC)) {
+		pr_warn("BTF.ext in non-native endianness is not supported\n");
+		return -ENOTSUP;
+	} else if (hdr->magic != BTF_MAGIC) {
 		pr_debug("Invalid BTF.ext magic:%x\n", hdr->magic);
 		return -EINVAL;
 	}