[PATCH v1 08/14] bfd: parse Object Attributes v2's section in input object files
Matthieu Longo
matthieu.longo@arm.com
Fri Mar 21 17:14:42 GMT 2025
This patch adds to BFD the capability of parsing the Object Attributes v2
(OAv2) stored into the section defined by the backend (i.e. .ARM.attributes
for AArch64).
An OAv2 section is organized with the following syntactic structure:
<format-version: 'A'>
[ <uint32: subsection-length>
<NTBS: vendor-name>
<uint8: optionality>
<uint8: OAv2's value encoding>
<attribute>*
]*
Once parsing is completed, OAv2 are stored in a list of subsections in
elf_obj_tdata.
---
bfd/elf-attrs.c | 214 +++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 212 insertions(+), 2 deletions(-)
diff --git a/bfd/elf-attrs.c b/bfd/elf-attrs.c
index 002b7fe3c59..5f1cf5cbb1a 100644
--- a/bfd/elf-attrs.c
+++ b/bfd/elf-attrs.c
@@ -770,7 +770,214 @@ bfd_elf_parse_attr_section_v1 (bfd *abfd, bfd_byte *p, bfd_byte *p_end)
}
}
-/* Parse an object attributes section. */
+/* A helper struct for parsing, which returns the parsed object, the number of
+ bytes read, and whether or not an error occurred. */
+typedef struct {
+ /* Was an error met during parsing. */
+ bool err;
+ /* How many bytes were read ? (until error if an error occurred) */
+ uint64_t read;
+ /* The parsed object. */
+ void *object;
+} BufferReadOp_t ;
+
+#define READ_ULEB128(abfd, var, cursor, end, op) \
+ do \
+ { \
+ bfd_byte *_begin = cursor; \
+ (var) = _bfd_safe_read_leb128 (abfd, &cursor, false, end);\
+ op.read += cursor - _begin; \
+ } \
+ while (0)
+
+#define READ_NTBS(abfd, var, cursor, end, op) \
+ do \
+ { \
+ (var) = strdup ((const char*) cursor); \
+ size_t read_ = strnlen (var, end - cursor) + 1; \
+ op.read += read_; \
+ (cursor) += read_; \
+ } \
+ while (0)
+
+#define READ_UINT8(abfd, var, cursor, end, op) \
+ do \
+ { \
+ (var) = bfd_get_8 (abfd, (cursor)); \
+ (cursor) += sizeof(uint8_t); \
+ op.read += sizeof(uint8_t); \
+ } \
+ while (0)
+
+/* Parse an object attribute (v2 only). */
+static BufferReadOp_t
+bfd_elf_parse_attr_v2 (bfd *abfd,
+ bfd_byte *cursor,
+ bfd_byte *const end,
+ obj_attr_encoding_v2 attr_type)
+{
+ BufferReadOp_t op = { .err = false, .read = 0, .object = NULL };
+
+ uint32_t attr_tag;
+ READ_ULEB128 (abfd, attr_tag, cursor, end, op);
+
+ union obj_attr_value_v2 vals;
+ switch (attr_type)
+ {
+ case NTBS:
+ READ_NTBS (abfd, vals.string_val, cursor, end, op);
+ break;
+ case ULEB128:
+ READ_ULEB128 (abfd, vals.uint_val, cursor, end, op);
+ break;
+ }
+
+ op.object = _bfd_elf_obj_attr_v2_init (attr_tag, vals);
+ return op;
+}
+
+/* Parse a subsection (object attributes v2 only). */
+static BufferReadOp_t
+bfd_elf_parse_attrs_subsection_v2 (bfd *abfd,
+ bfd_byte *cursor,
+ const uint64_t max_read)
+{
+ BufferReadOp_t op = { .err = false, .read = 0, .object = NULL };
+
+ const uint32_t F_SUBSECTION_LEN = sizeof(uint32_t);
+ /* The minimum subsection length is 5: 4 bytes for the length itself, and 1
+ byte for an empty NUL-terminated string, and no vendor-data. */
+ const uint32_t F_MIN_SUBSECTION_DATA_LEN = F_SUBSECTION_LEN + 1;
+
+ if (max_read <= F_SUBSECTION_LEN)
+ {
+ _bfd_error_handler (_("%pB: error: attributes subsection ends "
+ "prematurely"), abfd);
+ bfd_set_error (bfd_error_malformed_archive);
+ return op;
+ }
+
+ uint32_t subsection_len = bfd_get_32 (abfd, cursor);
+ op.read += F_SUBSECTION_LEN;
+ cursor += F_SUBSECTION_LEN;
+ if (subsection_len > max_read)
+ {
+ _bfd_error_handler (_("%pB: error: bad subsection length (%u > max=%lu)"),
+ abfd, subsection_len, max_read);
+ bfd_set_error (bfd_error_malformed_archive);
+ op.err = true;
+ return op;
+ }
+ /* PR 17531: file: 001-101425-0.004 */
+ else if (subsection_len < F_MIN_SUBSECTION_DATA_LEN)
+ {
+ _bfd_error_handler (_("%pB: error: subsection length of %u is too small"),
+ abfd, subsection_len);
+ bfd_set_error (bfd_error_malformed_archive);
+ op.err = true;
+ return op;
+ }
+
+ size_t subsection_name_len = strnlen ((char *) cursor, subsection_len) + 1;
+ if (subsection_name_len >= subsection_len)
+ {
+ _bfd_error_handler (_("%pB: error: subsection name seems corrupted "
+ "(missing '\\0')"), abfd);
+ bfd_set_error (bfd_error_malformed_archive);
+ op.err = true;
+ return op;
+ }
+ /* Note: if the length of the subsection name is 0 (i.e. the string is '\0'),
+ it is still considered a valid name, even if it is not particularly
+ usefull. */
+
+ unsigned char * const end = cursor + subsection_len - F_SUBSECTION_LEN;
+ BFD_ASSERT (cursor < end);
+
+ const char* subsection_name;
+ READ_NTBS (abfd, subsection_name, cursor, end, op);
+
+ uint8_t optional_raw;
+ READ_UINT8 (abfd, optional_raw, cursor, end, op);
+
+ if (optional_raw > 1)
+ {
+ _bfd_error_handler (_("%pB: error: optional value seems corrupted, got"
+ " %u but only 0x0 (false) or 0x1 (true) are "
+ "valid values."), abfd, optional_raw);
+ bfd_set_error (bfd_error_malformed_archive);
+ op.err = true;
+ free ((void*) subsection_name);
+ return op;
+ }
+
+ uint8_t attr_type_raw;
+ READ_UINT8 (abfd, attr_type_raw, cursor, end, op);
+ if (attr_type_raw > NTBS)
+ {
+ _bfd_error_handler (_("%pB: error: attribute type seems corrupted, got"
+ " %u but only 0x0 (ULEB128) or 0x1 (NTBS) are "
+ "valid types."), abfd, attr_type_raw);
+ bfd_set_error (bfd_error_malformed_archive);
+ op.err = true;
+ free ((void*) subsection_name);
+ return op;
+ }
+
+ const char *vendor_name = get_elf_backend_data (abfd)->obj_attrs_vendor;
+ obj_attr_subsection_scope_v2 scope =
+ (strncmp (subsection_name, vendor_name, strlen (vendor_name)) == 0)
+ ? SUBSEC_PUBLIC
+ : SUBSEC_PRIVATE;
+
+ obj_attr_subsection_v2 *subsec =
+ _bfd_elf_obj_attr_subsection_v2_init (subsection_name, scope, optional_raw,
+ attr_type_raw);
+ while (cursor < end)
+ {
+ BufferReadOp_t op_ =
+ bfd_elf_parse_attr_v2 (abfd, cursor, end, attr_type_raw);
+ LINKED_LIST_APPEND(obj_attr_v2) (subsec, op_.object);
+ op.read += op_.read;
+ cursor += op_.read;
+ }
+
+ op.object = subsec;
+
+ BFD_ASSERT (cursor == end);
+
+ return op;
+}
+
+/* Parse the list of subsections (object attributes v2 only). */
+static void
+bfd_elf_parse_attr_section_v2 (bfd *abfd,
+ Elf_Internal_Shdr *hdr,
+ bfd_byte *cursor)
+{
+ obj_attr_subsection_list *subsecs = &elf_obj_attr_subsections (abfd);
+ BufferReadOp_t op;
+ for (uint64_t remaining = hdr->sh_size - 1; // already read 'A'
+ remaining > 0;
+ remaining -= op.read, cursor += op.read)
+ {
+ op = bfd_elf_parse_attrs_subsection_v2 (abfd, cursor, remaining);
+ if (op.err)
+ {
+ _bfd_error_handler (_("%pB: error: could not parse subsection at "
+ "offset %lx"),
+ abfd, hdr->sh_size - remaining);
+ bfd_set_error (bfd_error_wrong_format);
+ break;
+ }
+ else
+ LINKED_LIST_APPEND(obj_attr_subsection_v2) (subsecs,
+ (obj_attr_subsection_v2 *) op.object);
+ }
+}
+
+/* Parse an object attributes section.
+ Note: The parsing setup is common between object attributes v1 and v2. */
void
_bfd_elf_parse_attributes (bfd *abfd, Elf_Internal_Shdr * hdr)
{
@@ -808,7 +1015,10 @@ _bfd_elf_parse_attributes (bfd *abfd, Elf_Internal_Shdr * hdr)
++cursor;
- bfd_elf_parse_attr_section_v1 (abfd, cursor, data + hdr->sh_size);
+ if (get_elf_backend_data (abfd)->obj_attrs_version == 2)
+ bfd_elf_parse_attr_section_v2 (abfd, hdr, cursor);
+ else
+ bfd_elf_parse_attr_section_v1 (abfd, cursor, data + hdr->sh_size);
free_data:
free (data);
--
2.49.0
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