[PATCH v0 06/15] readelf: add support to dump build attributes v2
Matthieu Longo
matthieu.longo@arm.com
Mon Mar 10 17:51:19 GMT 2025
From: Richard Ball <richard.ball@arm.com>
Co-Authored-By: Matthieu Longo <matthieu.longo@arm.com>
---
bfd/elf-attrs.h | 18 +++
binutils/readelf.c | 261 ++++++++++++++++++++++++++++++++++++++++++
include/elf/aarch64.h | 13 +++
3 files changed, 292 insertions(+)
diff --git a/bfd/elf-attrs.h b/bfd/elf-attrs.h
index 5d41bb98538..a4af0da1f68 100644
--- a/bfd/elf-attrs.h
+++ b/bfd/elf-attrs.h
@@ -100,3 +100,21 @@ typedef struct obj_attr_subsection_list
/* The size of the list. */
uint64_t size;
} obj_attr_subsection_list;
+
+typedef struct
+{
+ const uint32_t tag;
+ const char * name;
+ union obj_attr_value_v2 default_value;
+} known_tag_v2;
+
+#define OBJ_ATTR_TAG_v2(s) "Tag_" # s
+typedef struct
+{
+ const char *subsec_name;
+ const known_tag_v2 *known_tags;
+ const bool optional;
+ const obj_attr_encoding_v2 encoding;
+ const size_t len;
+} known_subsection_v2;
+
diff --git a/binutils/readelf.c b/binutils/readelf.c
index dd1871d8c75..b69180e4e33 100644
--- a/binutils/readelf.c
+++ b/binutils/readelf.c
@@ -58,6 +58,7 @@
#define BFD64
#include "bfd.h"
+#include "elf-attrs.h"
#include "bucomm.h"
#include "elfcomm.h"
#include "demanguse.h"
@@ -19456,6 +19457,263 @@ free_data:
return res;
}
+static unsigned char *
+display_attr_v2 (unsigned char * cursor,
+ const unsigned char * const end,
+ const char *subsec_name,
+ obj_attr_encoding_v2 value_encoding)
+{
+ static const known_tag_v2 known_tags_aeabi_feature_and_bits [] =
+ {
+ {Tag_Feature_BTI, "Feature_BTI", {0}},
+ {Tag_Feature_PAC, "Feature_PAC", {0}},
+ {Tag_Feature_GCS, "Feature_GCS", {0}},
+ };
+ static const known_tag_v2 known_tags_aeabi_pauthabi [] =
+ {
+ {Tag_PAuth_Platform, "PAuth_Platform", {0}},
+ {Tag_PAuth_Schema, "PAuth_Schema", {0}},
+ };
+ static const known_subsection_v2 known_subsections[] =
+ {
+ {
+ .subsec_name = "aeabi_feature_and_bits",
+ .known_tags = known_tags_aeabi_feature_and_bits,
+ .optional = true,
+ .encoding = ULEB128,
+ .len = sizeof (known_tags_aeabi_feature_and_bits),
+ },
+ {
+ .subsec_name = "aeabi_pauthabi",
+ .known_tags = known_tags_aeabi_pauthabi,
+ .optional = false,
+ .encoding = ULEB128,
+ .len = sizeof (known_tags_aeabi_pauthabi),
+ },
+ };
+
+ const known_subsection_v2 *
+ identify_subsection_ (const char* name)
+ {
+ for (unsigned i = 0; i < ARRAY_SIZE (known_subsections); ++i)
+ if (strcmp (name, known_subsections[i].subsec_name) == 0)
+ return &known_subsections[i];
+ return NULL;
+ }
+
+ const known_tag_v2 *
+ identify_tag_ (const known_subsection_v2* subsec,
+ uint32_t tag)
+ {
+ for (unsigned i = 0; i < subsec->len; ++i)
+ {
+ const known_tag_v2 *known_tag = &subsec->known_tags[i];
+ if (known_tag->tag == tag)
+ return known_tag;
+ }
+ return NULL;
+ }
+
+ uint32_t tag;
+ READ_ULEB (tag, cursor, end);
+
+ const known_tag_v2 *tag_info = NULL;
+ const known_subsection_v2 *subsec_info = identify_subsection_ (subsec_name);
+ if (subsec_info != NULL)
+ tag_info = identify_tag_ (subsec_info, tag);
+
+ if (tag_info != NULL)
+ printf (" Tag_%s: ", tag_info->name);
+ else
+ printf (" Tag_unknown_%u: ", tag);
+
+ switch (value_encoding)
+ {
+ case NTBS:
+ cursor = display_tag_value (-1, cursor, end);
+ break;
+ case ULEB128:
+ cursor = display_tag_value (0, cursor, end);
+ break;
+ }
+
+ return cursor;
+}
+
+typedef struct {
+ bool err;
+ uint64_t read;
+} BufferReadOp_t ;
+
+static BufferReadOp_t
+elf_parse_attrs_subsection_v2 (unsigned char* cursor,
+ const uint64_t max_read,
+ const char* public_name)
+{
+ BufferReadOp_t op = { .err = false, .read = 0 };
+
+ 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)
+ {
+ error (_("Build attributes section ends prematurely\n"));
+ return op;
+ }
+ uint32_t subsection_len = byte_get (cursor, F_SUBSECTION_LEN);
+ op.read += F_SUBSECTION_LEN;
+ cursor += F_SUBSECTION_LEN;
+ if (subsection_len > max_read)
+ {
+ error (_("Bad subsection length (%u > max=%lu)\n"),
+ subsection_len, max_read);
+ // error, but still try to display the content until meeting a more serious error.
+ subsection_len = max_read;
+ op.err = true;
+ }
+ /* PR 17531: file: 001-101425-0.004 */
+ else if (subsection_len < F_MIN_SUBSECTION_DATA_LEN)
+ {
+ error (_("Subsection length of %u is too small\n"), subsection_len);
+ op.err = true;
+ return op;
+ }
+
+ size_t subsection_name_len = strnlen ((char *) cursor, subsection_len) + 1;
+ if (subsection_name_len >= subsection_len)
+ {
+ error (_("Subsection name seems corrupted (missing '\\0')\n"));
+ op.err = true;
+ return op;
+ }
+ //if (subsection_name_len == 0)
+ // // do something here when the string is '\0'
+
+ unsigned char * const end = cursor + subsection_len - F_SUBSECTION_LEN;
+ while (cursor < end)
+ {
+ const char* subsec_name = (const char*) cursor;
+ printf (_(" - Name: %s\n"), subsec_name);
+ bool public_subsection =
+ strncmp (subsec_name, public_name, strlen (public_name)) == 0;
+ cursor += subsection_name_len;
+ op.read += subsection_name_len;
+
+ printf (" Scope: %s\n", public_subsection ? "public" : "private");
+ printf (" Length: %u\n", subsection_len);
+
+ uint8_t optional;
+ READ_ULEB (optional, cursor, end);
+ op.read += 1;
+
+ if (optional > 1)
+ {
+ error (_("Optional value seems corrupted, got %u but only"
+ " 0x0 (false) or 0x1 (true) are valid values."), optional);
+ op.err = true;
+ op.read = subsection_len;
+ return op;
+ }
+
+ printf (" Optional: %s\n", optional ? "True" : "False");
+
+ uint8_t value_encoding_raw;
+ READ_ULEB (value_encoding_raw, cursor, end);
+ op.read += 1;
+
+ if (value_encoding_raw > NTBS)
+ {
+ error (_("Attribute type seems corrupted, got %u but only 0x0 (ULEB128)"
+ " or 0x1 (NTBS) are valid types."), value_encoding_raw);
+ op.err = true;
+ op.read = subsection_len;
+ return op;
+ }
+
+ enum obj_attr_encoding_v2 value_encoding = value_encoding_raw;
+ switch (value_encoding)
+ {
+ case ULEB128:
+ printf (" Encoding: ULEB128\n");
+ break;
+ case NTBS:
+ printf (" Encoding: asciz\n");
+ break;
+ }
+
+ printf (" Values:\n");
+ while (cursor < end)
+ {
+ unsigned char* cursor_new =
+ display_attr_v2 (cursor, end, subsec_name, value_encoding);
+ op.read += (cursor_new - cursor);
+ cursor = cursor_new;
+ }
+ putchar ('\n');
+ }
+
+ if (cursor != end)
+ abort();
+
+ return op;
+}
+
+static bool
+process_attributes_v2 (Filedata *filedata,
+ const char *public_name,
+ uint32_t section_type)
+{
+ /* Find the section header so that we get the size. */
+ Elf_Internal_Shdr *sec_hdr = find_section_by_type (filedata, section_type);
+ if (sec_hdr == NULL)
+ /* No section, exit without error. */
+ return true;
+
+ unsigned char * const data = (unsigned char*)
+ get_data (NULL, filedata, sec_hdr->sh_offset, 1, sec_hdr->sh_size,
+ _("build attributes"));
+ if (data == NULL)
+ return false;
+
+ unsigned char *cursor = data;
+ bool res = true;
+
+ /* The first character is the version of the attributes.
+ Currently only version 1, (aka 'A') is recognised here. */
+ if (*cursor != 'A')
+ {
+ error (_("Unknown attributes version '%c'(%d) - expecting 'A'\n"),
+ *cursor, *cursor);
+ res = false;
+ goto free_data;
+ }
+
+ ++cursor;
+
+ printf (("Subsections:\n"));
+ BufferReadOp_t op;
+ for (uint64_t remaining = sec_hdr->sh_size - 1; // already read 'A'
+ remaining > 1;
+ remaining -= op.read, cursor += op.read)
+ {
+ op = elf_parse_attrs_subsection_v2 (cursor, remaining, public_name);
+ if (op.err)
+ {
+ error (_("Cannot parse subsection at offset %lx"),
+ sec_hdr->sh_size - remaining);
+ res = false;
+ goto free_data;
+ }
+ }
+
+free_data:
+ free ((void*) data);
+
+ return res;
+}
+
/* DATA points to the contents of a MIPS GOT that starts at VMA PLTGOT.
Print the Address, Access and Initial fields of an entry at VMA ADDR
and return the VMA of the next entry, or -1 if there was a problem.
@@ -23444,6 +23702,9 @@ process_arch_specific (Filedata * filedata)
display_arm_attribute,
display_generic_attribute);
+ case EM_AARCH64:
+ return process_attributes_v2 (filedata, "aeabi", SHT_AARCH64_ATTRIBUTES);
+
case EM_MIPS:
case EM_MIPS_RS3_LE:
return process_mips_specific (filedata);
diff --git a/include/elf/aarch64.h b/include/elf/aarch64.h
index e218e07fa73..c076174a7ac 100644
--- a/include/elf/aarch64.h
+++ b/include/elf/aarch64.h
@@ -57,6 +57,19 @@
#define STO_AARCH64_VARIANT_PCS 0x80 /* Symbol may follow different call
convention from the base PCS. */
+/* Tags used in aeabi_feature_and_bits subsection. */
+typedef enum Tag_Feature_XXX {
+ Tag_Feature_BTI = 0,
+ Tag_Feature_PAC = 1,
+ Tag_Feature_GCS = 2,
+} Tag_Feature_XXX;
+
+/* Tags used in aeabi_pauthabi subsection. */
+typedef enum Tag_PAuth_XXX {
+ Tag_PAuth_Platform = 1,
+ Tag_PAuth_Schema = 2,
+} Tag_PAuth_XXX;
+
/* Relocation types. */
START_RELOC_NUMBERS (elf_aarch64_reloc_type)
--
2.48.1
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