Hi Mark,
On Thu, Mar 26, 2026 at 12:48 PM Mark Wielaard <[email protected]> wrote:
>
> DWARF Package files (.dwp) might contain a .debug_cu_index and/or
> .debug_tu_index section. Print the contents of these sections. Handles
> version 2 (DWARF4 + GNU Debugfission extension), version 5
> (standardized) and version 6 (prelimenary, adds 64bit offsets). Use
> the existing dwp4 and dwp5 testfiles.
>
> * src/readelf.c (options): Add cu_index to debug-dump docs.
> (section_e): Add section_cu_index.
> (section_all): Likewise.
> (parse_opt): handle "cu_index" arg for debug-dump.
> (dwarf_section_short_string): New static function.
> (print_cu_index_section): Likewise.
> (print_debug): Move up implicit_info and explicit_info. Only
> search for skeleton file if .debug_info is needed. Handle both
> .debug_cu_index and .debug_tu_index through
> print_cu_index_section.
> * tests/run-readelf-cu-index.sh: New test.
> * tests/Makefile.am (TESTS): Add run-readelf-cu-index.sh.
> (EXTRA_DIST): Likewise.
>
> Signed-off-by: Mark Wielaard <[email protected]>
> ---
> src/readelf.c | 276 +++++++++++++++++++++++++++++++++-
> tests/Makefile.am | 2 +
> tests/run-readelf-cu-index.sh | 99 ++++++++++++
> 3 files changed, 369 insertions(+), 8 deletions(-)
> create mode 100755 tests/run-readelf-cu-index.sh
>
> diff --git a/src/readelf.c b/src/readelf.c
> index 6d4cde9f59c5..5a897e6cd33d 100644
> --- a/src/readelf.c
> +++ b/src/readelf.c
> @@ -1,6 +1,6 @@
> /* Print information from ELF file in human-readable form.
> Copyright (C) 1999-2018 Red Hat, Inc.
> - Copyright (C) 2023, 2025 Mark J. Wielaard <[email protected]>
> + Copyright (C) 2023, 2025, 2026 Mark J. Wielaard <[email protected]>
> This file is part of elfutils.
>
> This file is free software; you can redistribute it and/or modify
> @@ -141,8 +141,9 @@ static const struct argp_option options[] =
> { NULL, 0, NULL, 0, N_("Additional output selection:"), 0 },
> { "debug-dump", 'w', "SECTION", OPTION_ARG_OPTIONAL,
> N_("Display DWARF section content. SECTION can be one of abbrev, addr, "
> - "aranges, decodedaranges, frame, gdb_index, info, info+, loc, line, "
> - "decodedline, ranges, pubnames, str, macinfo, macro or exception"), 0
> },
> + "aranges, cu_index, decodedaranges, frame, gdb_index, info, info+, "
> + "loc, line, decodedline, ranges, pubnames, str, macinfo, macro or "
> + "exception"), 0 },
> { "hex-dump", 'x', "SECTION", 0,
> N_("Dump the uninterpreted contents of SECTION, by number or name"), 0 },
> { "strings", 'p', "SECTION", OPTION_ARG_OPTIONAL,
> @@ -288,11 +289,13 @@ static enum section_e
> section_macro = 4096, /* .debug_macro */
> section_addr = 8192, /* .debug_addr */
> section_types = 16384, /* .debug_types (implied by .debug_info) */
> + section_cu_index = 32768, /* .debug_cu_index (include .debug_tu_index)
> */
> section_all = (section_abbrev | section_aranges | section_frame
> | section_info | section_line | section_loc
> | section_pubnames | section_str | section_macinfo
> | section_ranges | section_exception | section_gdb_index
> - | section_macro | section_addr | section_types)
> + | section_macro | section_addr | section_types
> + | section_cu_index)
> } print_debug_sections, implicit_debug_sections;
>
> /* Select hex dumping of sections. */
> @@ -789,6 +792,8 @@ parse_opt (int key, char *arg,
> print_debug_sections |= section_exception;
> else if (strcmp (arg, "gdb_index") == 0)
> print_debug_sections |= section_gdb_index;
> + else if (strcmp (arg, "cu_index") == 0)
> + print_debug_sections |= section_cu_index;
> else
> {
> fprintf (stderr, _("Unknown DWARF debug section `%s'.\n"),
> @@ -4874,6 +4879,48 @@ dwarf_line_content_description_string (unsigned int
> kind)
> }
>
>
> +/* Doesn't use dwarf_section_name because we want short (max 6 chars)
> + lowercase strings and result depends on version. */
> +static const char *
> +dwarf_section_short_string (unsigned int vers, unsigned kind)
> +{
> + const char *sec_str = NULL;
> + if (vers == 2 && (kind == 7 || kind == 8)) /* macinfo or macro */
> + sec_str = "macro";
> + else
> + {
> + switch (kind)
> + {
> + case DW_SECT_INFO:
> + sec_str = "info";
> + break;
> + case DW_SECT_TYPES:
> + sec_str = "types"; /* Only really valid for version 2. */
> + break;
> + case DW_SECT_ABBREV:
> + sec_str = "abbrv";
> + break;
> + case DW_SECT_LINE:
> + sec_str = "line";
> + break;
> + case DW_SECT_LOCLISTS:
> + sec_str = "locs";
> + break;
> + case DW_SECT_STR_OFFSETS:
> + sec_str = "stroff";
> + break;
> + case DW_SECT_MACRO:
> + sec_str = "macro";
> + break;
> + case DW_SECT_RNGLISTS:
> + sec_str = "rngs";
> + break;
> + }
> + }
> +
> + return sec_str;
> +}
> +
> /* Used by all dwarf_foo_name functions. */
> static const char *
> string_or_unknown (const char *known, unsigned int code,
> @@ -12176,6 +12223,214 @@ print_gdb_index_section (Dwfl_Module *dwflmod, Ebl
> *ebl,
> fprintf (out, "<unknown>\n");
> }
>
> +/* Print the content of the '.debug_cu_index' or '.debug_tu_index'
> + sections. */
> +static void
> +print_cu_index_section (Dwfl_Module *dwflmod __attribute__ ((unused)),
> + Ebl *ebl, GElf_Ehdr *ehdr __attribute__ ((unused)),
> + Elf_Scn *scn, GElf_Shdr *shdr, Dwarf *dbg,
> + FILE *out)
> +{
> + const char *sname = section_name (ebl, shdr);
> + fprintf (out, _("\nDWARF section [%2zu] '%s' at offset %#" PRIx64
> + " contains %" PRId64 " bytes :\n"),
> + elf_ndxscn (scn), sname,
> + (uint64_t) shdr->sh_offset, (uint64_t) shdr->sh_size);
> +
> + Elf_Data *data = elf_rawdata (scn, NULL);
> +
> + if (unlikely (data == NULL))
> + {
> + error (0, 0, _("cannot get %s content: %s"), sname, elf_errmsg (-1));
> + return;
> + }
> +
> + bool is_tu = sname != NULL && strcmp (sname, ".debug_tu_index") == 0;
> +
> + const unsigned char *readp = data->d_buf;
> + const unsigned char *const dataend = readp + data->d_size;
> +
> + if (unlikely (readp > dataend - 4))
> + {
> + invalid_data:
> + error (0, 0, _("invalid data"));
> + return;
> + }
> +
> + /* If read as 4 bytes the version is 2, it is GNU DebugFission for
> + DWARF 5, otherwise the version is in the first 2 bytes, with 2
> + bytes padding. */
> + int32_t vers = read_4ubyte_unaligned (dbg, readp);
> + if (vers != 2)
> + vers = read_2ubyte_unaligned (dbg, readp);
> + fprintf (out, _(" Version: %8" PRId32 "\n"), vers);
> +
> + /* There used to be a version 1, which we don't support, but is
> + described at https://gcc.gnu.org/wiki/DebugFissionDWP
> + Version 2 is GNU DebugFission for DWARF4.
> + Version 5 is the standardized DWARF5 index.
> + Version 6 supports DWARF64 as described in
> + https://dwarfstd.org/issues/220708.2.html */
> + if (vers != 2 && vers != 5 && vers != 6)
> + {
> + error (0, 0, _("unknown version, cannot parse section"));
> + return;
> + }
> +
> + uint8_t offset_size_flag = 0;
> + if (vers < 2)
vers < 2 is always false here since there's an early return above if
vers isn't 2, 5 or 6.
> + readp += 4;
> + else
> + {
> + readp += 3;
> + offset_size_flag = *readp;
> + fprintf (out, _(" Offset Size: %4" PRIu8 "\n"),
> + offset_size_flag == 0 ? 32 : 64);
> + readp++;
> + }
> +
> + const unsigned char off_bytes = offset_size_flag == 0 ? 4 : 8;
> +
> + if (unlikely (readp > dataend - 4))
> + goto invalid_data;
> + uint32_t section_count = read_4ubyte_unaligned (dbg, readp);
> + fprintf (out, _(" Columns: %8" PRId32 "\n"), section_count);
> +
> + readp += 4;
> + if (unlikely (readp > dataend - 4))
> + goto invalid_data;
> + uint32_t unit_count = read_4ubyte_unaligned (dbg, readp);
> + fprintf (out, _(" Entries: %8" PRId32 "\n"), unit_count);
> +
> + readp += 4;
> + if (unlikely (readp > dataend - 4))
> + goto invalid_data;
> + uint32_t slot_count = read_4ubyte_unaligned (dbg, readp);
> + fprintf (out, _(" Slots: %8" PRId32 "\n"), slot_count);
> +
> + /* Really should be slot_count > 3 * unit_count / 2, but accept as
> + long as slot_count is at least unit_count. */
> + if (slot_count < unit_count)
> + {
> + error (0, 0, _("Must have at least as many slots as entries"));
> + return;
> + }
> +
> + readp += 4;
> +
> + /* Hash table starts directly after header (16 bytes). */
> + const unsigned char *hash_table = readp;
> + /* Indices (which slot is used for each hash id entry) start after
> + the hash table (ids of 8 bytes). */
> + const unsigned char *indices = hash_table + slot_count * 8;
> + /* Sections used starts after the indices, indices and hash table
> + have the same number of slots, indeces are 4 bytes each, */
> + const unsigned char *sections = indices + slot_count * 4;
> + /* Offset slots for each section follow the one row of sections. */
> + const unsigned char *offsets = sections + section_count * 4;
> + /* Size slots for each section follow the offsets (used rows). */
> + const unsigned char *lengths = (offsets +
> + unit_count * section_count * off_bytes);
> + const unsigned char *lengths_end = lengths + section_count * 4;
> +
> + /* Sanity check the above against dataend. */
> + if ((slot_count > UINT32_MAX / 8)
> + || (section_count > SIZE_MAX / off_bytes)
> + || (unit_count > SIZE_MAX / off_bytes)
> + || ((unit_count != 0) && (section_count > SIZE_MAX / unit_count))
> + || ((section_count != 0) && (unit_count > SIZE_MAX / section_count))
> + || (indices > dataend)
> + || (sections > dataend)
> + || (offsets > dataend)
> + || (lengths > dataend)
> + || (lengths_end > dataend))
> + goto invalid_data;
> +
> + fprintf (out, _("\n Offset table\n"));
> + fprintf (out, " slot %s", is_tu ? "tu sig" : "dwo id");
> + fprintf (out, " ");
> + for (size_t i = 0; i < section_count; i++)
> + {
> + uint32_t section = read_4ubyte_unaligned (dbg, sections + i * 4);
> + const char *sec_str = dwarf_section_short_string (vers, section);
> + if (sec_str == NULL)
> + fprintf (out, " ??? %2x", section);
> + else
> + fprintf (out, " %6s", sec_str);
> + }
> + fprintf (out, "\n");
> +
> + for (size_t i = 0; i < slot_count; i++)
> + {
> + uint64_t id;
> + uint32_t row;
> + id = read_8ubyte_unaligned (dbg, hash_table + i * 8);
> + row = read_4ubyte_unaligned (dbg, indices + i * 4);
> + /* Only print used rows. */
> + if (id != 0 && row != 0)
> + {
> + fprintf (out, " [%3zd] %016" PRIx64 " ", i, id);
> + if (row > unit_count)
> + {
> + error (0, 0, _("Row (%" PRIu32 ") larger than "
> + "unit count (%" PRIu32 ")"), row, unit_count);
> + continue;
> + }
> + /* Note row is one based, not zero based. */
> + const unsigned char *prow = (offsets
> + + ((row - 1) * section_count
> + * off_bytes));
> + for (size_t j = 0; j < section_count; j++)
> + {
> + uint32_t off = read_4ubyte_unaligned (dbg, prow + j * 4);
Is the hardcoded 4 intended in j * 4 or should it use off_bytes instead?
> + printf (" %6" PRIu32, off);
Should be fprintf (out, ...) instead of printf. This works if
--enable-thread-safety=no, but if =yes then helgrind warns about a
race condition in run-readelf-cu-index.sh due to this.
> + }
> + fprintf (out, "\n");
> + }
> + }
> +
> + fprintf (out, _("\n Size table\n"));
> + fprintf (out, " slot %s", is_tu ? "tu sig" : "dwo id");
> + fprintf (out, " ");
> + for (size_t i = 0; i < section_count; i++)
> + {
> + uint32_t section = read_4ubyte_unaligned (dbg, sections + i * 4);
> + const char *sec_str = dwarf_section_short_string (vers, section);
> + if (sec_str == NULL)
> + fprintf (out, " ??? %2x", section);
> + else
> + fprintf (out, " %6s", sec_str);
> + }
> + fprintf (out, "\n");
> +
> + for (size_t i = 0; i < slot_count; i++)
> + {
> + uint64_t id;
> + uint32_t row;
> + id = read_8ubyte_unaligned (dbg, hash_table + i * 8);
> + row = read_4ubyte_unaligned (dbg, indices + i * 4);
> + /* Only print used rows. */
> + if (id != 0 && row != 0)
> + {
> + fprintf (out, " [%3zd] %016" PRIx64 " ", i, id);
> + if (row > unit_count)
> + {
> + error (0, 0, _("Row (%" PRIu32 ") larger than "
> + "unit count (%" PRIu32 ")"), row, unit_count);
> + continue;
> + }
> + /* Note row is one based, not zero based. */
> + const unsigned char *prow = lengths + (row - 1) * section_count * 4;
> + for (size_t j = 0; j < section_count; j++)
> + {
> + uint32_t off = read_4ubyte_unaligned (dbg, prow + j * 4);
> + printf (" %6" PRIu32, off);
Should be fprintf (out, ...) here too.
> + }
> + fprintf (out, "\n");
> + }
> + }
> +}
> +
> /* Returns true and sets split DWARF CU id if there is a split compile
> unit in the given Dwarf, and no non-split units are found (before it). */
> static bool
> @@ -12293,6 +12548,11 @@ print_debug (Dwfl_Module *dwflmod, Ebl *ebl,
> GElf_Ehdr *ehdr)
> Dwarf *split_dbg = NULL;
> Dwarf_CU *split_cu = NULL;
>
> + /* If we need to implicitly or explicitly scan the debug_info section
> + we might need a bit more info, like a skeleton for split dwarf file).
> */
> + bool implicit_info = (implicit_debug_sections & section_info) != 0;
> + bool explicit_info = (print_debug_sections & section_info) != 0;
> +
> /* Before we start the real work get a debug context descriptor. */
> Dwarf_Addr dwbias;
> Dwarf *dbg = dwfl_module_getdwarf (dwflmod, &dwbias);
> @@ -12308,7 +12568,7 @@ print_debug (Dwfl_Module *dwflmod, Ebl *ebl,
> GElf_Ehdr *ehdr)
> dwfl_errmsg (-1));
> dbg = &dummy_dbg;
> }
> - else
> + else if (implicit_info || explicit_info)
> {
> /* If we are asked about a split dwarf (.dwo) file, use the user
> provided, or find the corresponding skeleton file. If we got
> @@ -12461,8 +12721,6 @@ print_debug (Dwfl_Module *dwflmod, Ebl *ebl,
> GElf_Ehdr *ehdr)
> we must make sure to handle it before handling any other debug
> section. Various other sections depend on the CU DIEs being
> scanned (silently) first. */
> - bool implicit_info = (implicit_debug_sections & section_info) != 0;
> - bool explicit_info = (print_debug_sections & section_info) != 0;
> if (implicit_info)
> {
> Elf_Scn *scn = NULL;
> @@ -12545,7 +12803,9 @@ print_debug (Dwfl_Module *dwflmod, Ebl *ebl,
> GElf_Ehdr *ehdr)
> print_debug_frame_hdr_section },
> { ".gcc_except_table", section_frame | section_exception,
> print_debug_exception_table },
> - { ".gdb_index", section_gdb_index, print_gdb_index_section }
> + { ".gdb_index", section_gdb_index, print_gdb_index_section },
> + { ".debug_cu_index", section_cu_index, print_cu_index_section },
> + { ".debug_tu_index", section_cu_index, print_cu_index_section },
> };
> const int ndebug_sections = (sizeof (debug_sections)
> / sizeof (debug_sections[0]));
> diff --git a/tests/Makefile.am b/tests/Makefile.am
> index 3702444d820f..9a005416a398 100644
> --- a/tests/Makefile.am
> +++ b/tests/Makefile.am
> @@ -149,6 +149,7 @@ TESTS = run-arextract.sh run-arsymtest.sh run-ar.sh
> newfile test-nlist \
> run-nm-self.sh run-readelf-self.sh run-readelf-info-plus.sh \
> run-readelf-compressed.sh \
> run-readelf-const-values.sh \
> + run-readelf-cu-index.sh \
> run-varlocs-self.sh run-exprlocs-self.sh \
> run-readelf-test1.sh run-readelf-test2.sh run-readelf-test3.sh \
> run-readelf-test4.sh run-readelf-twofiles.sh \
> @@ -368,6 +369,7 @@ EXTRA_DIST = run-arextract.sh run-arsymtest.sh run-ar.sh \
> run-readelf-compressed.sh \
> run-readelf-compressed-zstd.sh \
> run-readelf-const-values.sh testfile-const-values.debug.bz2 \
> + run-readelf-cu-index.sh \
> run-addrcfi.sh run-dwarfcfi.sh \
> testfile11-debugframe.bz2 testfile12-debugframe.bz2 \
> testfileaarch64-debugframe.bz2 testfilearm-debugframe.bz2 \
> diff --git a/tests/run-readelf-cu-index.sh b/tests/run-readelf-cu-index.sh
> new file mode 100755
> index 000000000000..c92ba44420e3
> --- /dev/null
> +++ b/tests/run-readelf-cu-index.sh
> @@ -0,0 +1,99 @@
> +#! /bin/sh
> +# Copyright (C) 2026 Mark J. Wielaard <[email protected]>
> +# This file is part of elfutils.
> +#
> +# This file is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 3 of the License, or
> +# (at your option) any later version.
> +#
> +# elfutils is distributed in the hope that it will be useful, but
> +# WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program. If not, see <http://www.gnu.org/licenses/>.
> +
> +. $srcdir/test-subr.sh
> +
> +# See testfile-dwp.source.
> +testfiles testfile-dwp-4.dwp testfile-dwp-5.dwp
> +
> +testrun_compare ${abs_top_builddir}/src/readelf --debug-dump=cu_index
> testfile-dwp-4.dwp <<\EOF
> +
> +DWARF section [ 9] '.debug_cu_index' at offset 0x6c80 contains 376 bytes :
> + Version: 2
> + Offset Size: 32
> + Columns: 6
> + Entries: 3
> + Slots: 16
> +
> + Offset table
> + slot dwo id info abbrv line locs stroff macro
> + [ 0] 947a8b559fb59920 404 585 164 283 3748 3469
> + [ 5] afdbe8f5b7425c95 286 370 82 0 1876 1735
> + [ 9] 0682b8eb2e720699 0 0 0 0 0 0
> +
> + Size table
> + slot dwo id info abbrv line locs stroff macro
> + [ 0] 947a8b559fb59920 453 414 83 241 1908 1735
> + [ 5] afdbe8f5b7425c95 118 215 82 0 1872 1734
> + [ 9] 0682b8eb2e720699 286 370 82 283 1876 1735
> +
> +DWARF section [10] '.debug_tu_index' at offset 0x6df8 contains 328 bytes :
> + Version: 2
> + Offset Size: 32
> + Columns: 6
> + Entries: 2
> + Slots: 16
> +
> + Offset table
> + slot tu sig types abbrv line locs stroff macro
> + [ 12] 063b4ae40c9316fc 111 370 82 0 1876 1735
> + [ 14] f35612db645f377e 0 0 0 0 0 0
> +
> + Size table
> + slot tu sig types abbrv line locs stroff macro
> + [ 12] 063b4ae40c9316fc 109 215 82 0 1872 1734
> + [ 14] f35612db645f377e 111 370 82 283 1876 1735
> +EOF
> +
> +testrun_compare ${abs_top_builddir}/src/readelf --debug-dump=cu_index
> testfile-dwp-5.dwp<<\EOF
> +
> +DWARF section [10] '.debug_tu_index' at offset 0x6ca1 contains 204 bytes :
> + Version: 5
> + Offset Size: 32
> + Columns: 7
> + Entries: 2
> + Slots: 4
> +
> + Offset table
> + slot tu sig info abbrv line locs stroff macro rngs
> + [ 0] 063b4ae40c9316fc 376 352 127 0 1884 1734 0
> + [ 2] f35612db645f377e 0 0 0 0 0 0 0
> +
> + Size table
> + slot tu sig info abbrv line locs stroff macro rngs
> + [ 0] 063b4ae40c9316fc 110 202 127 0 1880 1733 0
> + [ 2] f35612db645f377e 112 352 127 219 1884 1734 34
> +
> +DWARF section [11] '.debug_cu_index' at offset 0x6d6d contains 308 bytes :
> + Version: 5
> + Offset Size: 32
> + Columns: 7
> + Entries: 3
> + Slots: 8
> +
> + Offset table
> + slot dwo id info abbrv line locs stroff macro rngs
> + [ 2] 2970268d42208082 606 554 254 219 3764 3467 34
> + [ 3] 225988b4ba73f4b3 112 0 0 0 0 0 0
> + [ 6] 1082731073ccdfbe 486 352 127 0 1884 1734 0
> +
> + Size table
> + slot dwo id info abbrv line locs stroff macro rngs
> + [ 2] 2970268d42208082 403 394 129 201 1916 1734 67
> + [ 3] 225988b4ba73f4b3 264 352 127 219 1884 1734 34
> + [ 6] 1082731073ccdfbe 120 202 127 0 1880 1733 0
> +EOF
> --
> 2.53.0
>
