[PATCH v5 08/20] readelf: dump Object Attributes v2
Richard Earnshaw (lists)
Richard.Earnshaw@arm.com
Wed Jul 9 14:02:13 GMT 2025
On 07/07/2025 17:49, Matthieu Longo wrote:
> From: Richard Ball <richard.ball@arm.com>
>
This is still lacking a proper commit message.
> Co-Authored-By: Matthieu Longo <matthieu.longo@arm.com>
> ---
> binutils/readelf.c | 317 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 317 insertions(+)
>
> diff --git a/binutils/readelf.c b/binutils/readelf.c
> index 573024727f2..afefdc388fe 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"
> @@ -19430,6 +19431,318 @@ free_data:
> return res;
> }
>
> +typedef gas_symbol_t known_tag_v2;
> +typedef struct
> +{
> + const char *subsec_name;
> + const known_tag_v2 *known_tags;
> + const size_t len;
> +} _known_subsection_v2;
> +
> +static const known_tag_v2 known_tags_aeabi_feature_and_bits [] =
> +{
> + {"Tag_Feature_BTI", .value = {
> + .val.u32 = Tag_Feature_BTI,
> + .vtype = VALUE_U32
> + }},
> + {"Tag_Feature_PAC", .value = {
> + .val.u32 = Tag_Feature_PAC,
> + .vtype = VALUE_U32
> + }},
> + {"Tag_Feature_GCS", .value = {
> + .val.u32 = Tag_Feature_GCS,
> + .vtype = VALUE_U32
> + }},
> +};
> +static const known_tag_v2 known_tags_aeabi_pauthabi [] =
> +{
> + {"Tag_PAuth_Platform", .value = {
> + .val.u32 = Tag_PAuth_Platform,
> + .vtype = VALUE_U32
> + }},
> + {"Tag_PAuth_Schema", .value = {
> + .val.u32 = Tag_PAuth_Schema,
> + .vtype = VALUE_U32
> + }},
> +};
> +static const _known_subsection_v2 known_subsections[] =
> +{
> + {
> + .subsec_name = "aeabi_feature_and_bits",
> + .known_tags = known_tags_aeabi_feature_and_bits,
> + .len = ARRAY_SIZE (known_tags_aeabi_feature_and_bits),
> + },
> + {
> + .subsec_name = "aeabi_pauthabi",
> + .known_tags = known_tags_aeabi_pauthabi,
> + .len = ARRAY_SIZE (known_tags_aeabi_pauthabi),
> + },
> +};
> +
> +static 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;
> +}
> +
> +static 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->value.val.u32 == tag)
> + return known_tag;
> + }
> + return NULL;
> +}
> +
> +static unsigned char *
> +attr_v2_default_value_display (unsigned char *cursor,
> + const unsigned char *const end,
> + obj_attr_encoding_v2 value_encoding)
> +{
> + switch (value_encoding)
> + {
> + case OA_ENC_NTBS:
> + cursor = display_tag_value (-1, cursor, end);
> + break;
> + case OA_ENC_ULEB128:
> + cursor = display_tag_value (0, cursor, end);
> + break;
> + case OA_ENC_UNSET:
> + abort ();
> + }
> + return cursor;
> +}
> +
> +static unsigned char *
> +display_aarch64_attribute (unsigned char *cursor,
> + const unsigned char *const end,
> + const known_tag_v2 *tag_info,
> + obj_attr_encoding_v2 value_encoding)
> +{
> + printf (" %s: ", tag_info->identifier);
> + /* FIXME: implement a different display for PAuthABI values. */
> + return attr_v2_default_value_display (cursor, end, value_encoding);
> +}
> +
> +typedef unsigned char *(*display_arch_attr_t) (unsigned char *,
> + const unsigned char *const,
> + const known_tag_v2 *,
> + obj_attr_encoding_v2);
> +
> +static unsigned char *
> +display_attr_v2 (unsigned char *cursor,
> + const unsigned char *const end,
> + const char *subsec_name,
> + obj_attr_encoding_v2 value_encoding,
> + display_arch_attr_t display_arch_attr)
> +{
> + 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)
> + return display_arch_attr (cursor, end, tag_info, value_encoding);
> +
> + printf (" Tag_unknown_%u: ", tag);
> + return attr_v2_default_value_display (cursor, end, value_encoding);
> +}
> +
> +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,
> + display_arch_attr_t display_arch_attr)
> +{
> + 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;
> +
> + /* Handle cases where the attributes data is not strictly valid (e.g. due to
> + fuzzing). */
> + 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;
> + }
> + 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 == 1, i.e. the subsection name is '\0', we still
> + consider the name valid for dumping, and an empty string will be displayed.
> + However, in practice, such a name would be unexploitable by the linker
> + during the merge, thus the subsection would be dropped. */
> +
> + 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 (" Comprehension: %s\n", optional ? "optional" : "required");
> +
> + uint8_t value_encoding_raw;
> + READ_ULEB (value_encoding_raw, cursor, end);
> + op.read += 1;
> + enum obj_attr_encoding_v2 value_encoding
> + = obj_attr_encoding_v2_from_u8 (value_encoding_raw);
> +
> + if (value_encoding > OA_ENC_MAX)
> + {
> + 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;
> + }
> +
> + switch (value_encoding)
> + {
> + case OA_ENC_ULEB128:
> + printf (" Encoding: ULEB128\n");
> + break;
> + case OA_ENC_NTBS:
> + printf (" Encoding: NTBS\n");
> + break;
> + default:
> + abort ();
> + }
> +
> + printf (" Values:\n");
> + while (cursor < end)
> + {
> + unsigned char *cursor_new =
> + display_attr_v2 (cursor, end, subsec_name, value_encoding,
> + display_arch_attr);
> + 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,
> + display_arch_attr_t display_arch_attr)
> +{
> + /* 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'(0x%02x) - expecting 'A'\n"),
> + ISPRINT(*cursor) ? *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,
> + display_arch_attr);
> + if (op.err)
> + {
> + error (_("Cannot parse subsection at offset %lx"),
> + sec_hdr->sh_size - remaining);
> + res = false;
> + goto free_data;
> + }
> + }
> +
> +free_data:
> + free (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.
> @@ -23457,6 +23770,10 @@ process_arch_specific (Filedata * filedata)
> display_arm_attribute,
> display_generic_attribute);
>
> + case EM_AARCH64:
> + return process_attributes_v2 (filedata, "aeabi", SHT_AARCH64_ATTRIBUTES,
> + display_aarch64_attribute);
> +
> case EM_MIPS:
> case EM_MIPS_RS3_LE:
> return process_mips_specific (filedata);
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