Add name_of_main and language_of_main to the DWARF index
Commit Message
Eli Zaretskii <eliz@gnu.org> wrote:
> Your assignment is not on file yet, AFAICT. Was the paperwork
> completed, i.e. did you get a copy of the assignment signed by you and
> by the FSF? If not, you need to wait some more.
Huh, that's weird. I do have the copy, signed by both parties. Maybe it just
hasn't been filed yet? If you want, I could forward it to you.
> Thanks. The documentation parts are OK, but please fix the text to
> leave two spaces between sentences, not one.
Alright, I've fixed that.
Is there anything else I'm missing?
---
This patch adds a new section to the DWARF index containing the name
and the language of the main function symbol, gathered from
`cooked_index::get_main`, if available. Currently, for lack of a better name,
this section is called the "shortcut table". The way this name is both saved and
applied upon an index being loaded in mirrors how it is done in
`cooked_index_functions`, more specifically, the full name of the main function
symbol is saved and `set_objfile_main_name` is used to apply it after it is
loaded.
The main use case for this patch is in improving startup times when dealing with
large binaries. Currently, when an index is used, GDB has to expand symtabs
until it finds out what the language of the main function symbol is. For some
large executables, this may take a considerable amount of time to complete,
slowing down startup. This patch bypasses that operation by having both the name
and language of the main function symbol be provided ahead of time by the index.
In my testing (a binary with about 1.8GB worth of DWARF data) this change brings
startup time down from about 34 seconds to about 1.5 seconds.
---
gdb/NEWS | 2 ++
gdb/doc/gdb.texinfo | 23 +++++++++++++--
gdb/dwarf2/index-write.c | 47 +++++++++++++++++++++++++++----
gdb/dwarf2/read-gdb-index.c | 56 +++++++++++++++++++++++++++++++++++--
gdb/dwarf2/read.c | 13 +++++++--
gdb/dwarf2/read.h | 12 ++++++++
6 files changed, 142 insertions(+), 11 deletions(-)
Comments
> From: Matheus Branco Borella <dark.ryu.550@gmail.com>
> Cc: gdb-patches@sourceware.org,
> Matheus Branco Borella <dark.ryu.550@gmail.com>
> Date: Fri, 7 Jul 2023 12:00:22 -0300
>
> Eli Zaretskii <eliz@gnu.org> wrote:
> > Your assignment is not on file yet, AFAICT. Was the paperwork
> > completed, i.e. did you get a copy of the assignment signed by you and
> > by the FSF? If not, you need to wait some more.
>
> Huh, that's weird. I do have the copy, signed by both parties. Maybe it just
> hasn't been filed yet? If you want, I could forward it to you.
I see now that your assignment was added, but it's only for Emacs, not
for GDB.
> > Thanks. The documentation parts are OK, but please fix the text to
> > leave two spaces between sentences, not one.
>
> Alright, I've fixed that.
>
> Is there anything else I'm missing?
There's still the issue of copyright assignment for GDB contributions,
AFAICT.
On 7/7/23 17:00, Matheus Branco Borella via Gdb-patches wrote:
> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
I applied this patch and tried to build it, and ran into:
...
/data/vries/gdb/src/gdb/doc/gdb.texinfo:49297: warning: @item missing
argument
/data/vries/gdb/src/gdb/doc/gdb.texinfo:49302: warning: @item missing
argument
/data/vries/gdb/src/gdb/doc/gdb.texinfo:49308: warning: @item missing
argument
/data/vries/gdb/src/gdb/doc/gdb.texinfo:49321: `@end' expected `table',
but saw `enumerate'
make[3]: *** [Makefile:495: gdb.info] Error 1
...
Thanks,
- Tom
On 7/7/23 17:00, Matheus Branco Borella via Gdb-patches wrote:
> Is there anything else I'm missing?
There seem to be a lot of white space issues:
...
$ git show --pretty=%s --check | grep -v '^\+'
Add name_of_main and language_of_main to the DWARF index
gdb/dwarf2/index-write.c:1084: indent with spaces.
gdb/dwarf2/index-write.c:1206: indent with spaces.
gdb/dwarf2/index-write.c:1217: indent with spaces.
gdb/dwarf2/index-write.c:1218: indent with spaces.
gdb/dwarf2/index-write.c:1219: indent with spaces.
gdb/dwarf2/index-write.c:1221: indent with spaces.
gdb/dwarf2/index-write.c:1222: indent with spaces.
gdb/dwarf2/index-write.c:1223: indent with spaces.
gdb/dwarf2/read-gdb-index.c:622: indent with spaces.
gdb/dwarf2/read-gdb-index.c:777: trailing whitespace.
gdb/dwarf2/read-gdb-index.c:778: indent with spaces.
gdb/dwarf2/read-gdb-index.c:791: indent with spaces.
gdb/dwarf2/read-gdb-index.c:803: trailing whitespace.
gdb/dwarf2/read-gdb-index.c:804: trailing whitespace, indent with spaces.
gdb/dwarf2/read-gdb-index.c:805: indent with spaces.
gdb/dwarf2/read.h:248: trailing whitespace.
gdb/dwarf2/read.h:251: trailing whitespace.
gdb/dwarf2/read.h:252: trailing whitespace.
...
Furthermore, I can confirm that this fixes regressions with target board
gdb-index in test-cases:
- gdb.fortran/backtrace.exp
- gdb.fortran/info-main.exp
- gdb.dwarf2/main-subprogram.exp
- gdb.fortran/mixed-lang-stack.exp
Some of those are KFAIL-ed for
https://sourceware.org/bugzilla/show_bug.cgi?id=24549 .
So, you could add this to the commit message:
...
PR symtab/24549
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=24549
...
Thanks,
- Tom
On 7/7/23 20:00, Eli Zaretskii via Gdb-patches wrote:
>> From: Matheus Branco Borella <dark.ryu.550@gmail.com>
>> Cc: gdb-patches@sourceware.org,
>> Matheus Branco Borella <dark.ryu.550@gmail.com>
>> Date: Fri, 7 Jul 2023 12:00:22 -0300
>>
>> Eli Zaretskii <eliz@gnu.org> wrote:
>>> Your assignment is not on file yet, AFAICT. Was the paperwork
>>> completed, i.e. did you get a copy of the assignment signed by you and
>>> by the FSF? If not, you need to wait some more.
>>
>> Huh, that's weird. I do have the copy, signed by both parties. Maybe it just
>> hasn't been filed yet? If you want, I could forward it to you.
>
> I see now that your assignment was added, but it's only for Emacs, not
> for GDB.
>
>>> Thanks. The documentation parts are OK, but please fix the text to
>>> leave two spaces between sentences, not one.
>>
>> Alright, I've fixed that.
>>
>> Is there anything else I'm missing?
>
> There's still the issue of copyright assignment for GDB contributions,
> AFAICT.
Hi,
Just checking, any update on this?
I'd love to see this get committed.
Thanks,
- Tom
> Date: Fri, 4 Aug 2023 22:55:43 +0200
> Cc: gdb-patches@sourceware.org
> From: Tom de Vries <tdevries@suse.de>
>
> On 7/7/23 20:00, Eli Zaretskii via Gdb-patches wrote:
> > There's still the issue of copyright assignment for GDB contributions,
> > AFAICT.
>
> Hi,
>
> Just checking, any update on this?
Marco's assignment is on file now, so we are good to go.
@@ -3,6 +3,8 @@
*** Changes since GDB 13
+* DWARF index now contains information about the main function.
+
* The AArch64 'org.gnu.gdb.aarch64.pauth' Pointer Authentication feature string
has been deprecated in favor of the 'org.gnu.gdb.aarch64.pauth_v2' feature
string.
@@ -49093,13 +49093,14 @@ unless otherwise noted:
@enumerate
@item
-The version number, currently 8. Versions 1, 2 and 3 are obsolete.
+The version number, currently 9. Versions 1, 2 and 3 are obsolete.
Version 4 uses a different hashing function from versions 5 and 6.
Version 6 includes symbols for inlined functions, whereas versions 4
and 5 do not. Version 7 adds attributes to the CU indices in the
symbol table. Version 8 specifies that symbols from DWARF type units
(@samp{DW_TAG_type_unit}) refer to the type unit's symbol table and not the
-compilation unit (@samp{DW_TAG_comp_unit}) using the type.
+compilation unit (@samp{DW_TAG_comp_unit}) using the type. Version 9 adds
+the name and the language of the main function to the index.
@value{GDBN} will only read version 4, 5, or 6 indices
by specifying @code{set use-deprecated-index-sections on}.
@@ -49120,6 +49121,9 @@ The offset, from the start of the file, of the address area.
@item
The offset, from the start of the file, of the symbol table.
+@item
+The offset, from the start of the file, of the shortcut table.
+
@item
The offset, from the start of the file, of the constant pool.
@end enumerate
@@ -49196,6 +49200,21 @@ don't currently have a simple description of the canonicalization
algorithm; if you intend to create new index sections, you must read
the code.
+@item
+The shortcut table. This is a data structure with the following fields:
+
+@table @asis
+@item
+A 32-bit little-endian value indicating the language of the main function as a
+@code{DW_LANG_} constant. This value will be zero if main function information
+is not present.
+
+@item
+An @code{offset_type} value indicating the offset of the main function's name
+in the constant pool. This value must be ignored if the value for the language
+of main is zero.
+@ end table
+
@item
The constant pool. This is simply a bunch of bytes. It is organized
so that alignment is correct: CU vectors are stored first, followed by
@@ -1080,14 +1080,15 @@ write_gdbindex_1 (FILE *out_file,
const data_buf &types_cu_list,
const data_buf &addr_vec,
const data_buf &symtab_vec,
- const data_buf &constant_pool)
+ const data_buf &constant_pool,
+ const data_buf &shortcuts)
{
data_buf contents;
- const offset_type size_of_header = 6 * sizeof (offset_type);
+ const offset_type size_of_header = 7 * sizeof (offset_type);
offset_type total_len = size_of_header;
/* The version number. */
- contents.append_offset (8);
+ contents.append_offset (9);
/* The offset of the CU list from the start of the file. */
contents.append_offset (total_len);
@@ -1105,6 +1106,10 @@ write_gdbindex_1 (FILE *out_file,
contents.append_offset (total_len);
total_len += symtab_vec.size ();
+ /* The offset of the shortcut table from the start of the file. */
+ contents.append_offset (total_len);
+ total_len += shortcuts.size ();
+
/* The offset of the constant pool from the start of the file. */
contents.append_offset (total_len);
total_len += constant_pool.size ();
@@ -1116,6 +1121,7 @@ write_gdbindex_1 (FILE *out_file,
types_cu_list.file_write (out_file);
addr_vec.file_write (out_file);
symtab_vec.file_write (out_file);
+ shortcuts.file_write (out_file);
constant_pool.file_write (out_file);
assert_file_size (out_file, total_len);
@@ -1193,6 +1199,34 @@ write_cooked_index (cooked_index *table,
}
}
+/* Write shortcut information. */
+
+static void
+write_shortcuts_table (cooked_index *table, data_buf& shortcuts,
+ data_buf& cpool)
+{
+ const auto main_info = table->get_main ();
+ size_t main_name_offset = 0;
+ dwarf_source_language dw_lang = (dwarf_source_language)0;
+
+ if (main_info != nullptr)
+ {
+ dw_lang = main_info->per_cu->dw_lang;
+
+ if (dw_lang != 0)
+ {
+ auto_obstack obstack;
+ const auto main_name = main_info->full_name (&obstack, true);
+
+ main_name_offset = cpool.size ();
+ cpool.append_cstr0 (main_name);
+ }
+ }
+
+ shortcuts.append_uint (4, BFD_ENDIAN_LITTLE, dw_lang);
+ shortcuts.append_offset (main_name_offset);
+}
+
/* Write contents of a .gdb_index section for OBJFILE into OUT_FILE.
If OBJFILE has an associated dwz file, write contents of a .gdb_index
section for that dwz file into DWZ_OUT_FILE. If OBJFILE does not have an
@@ -1270,11 +1304,14 @@ write_gdbindex (dwarf2_per_bfd *per_bfd, cooked_index *table,
write_hash_table (&symtab, symtab_vec, constant_pool);
+ data_buf shortcuts;
+ write_shortcuts_table (table, shortcuts, constant_pool);
+
write_gdbindex_1(out_file, objfile_cu_list, types_cu_list, addr_vec,
- symtab_vec, constant_pool);
+ symtab_vec, constant_pool, shortcuts);
if (dwz_out_file != NULL)
- write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {});
+ write_gdbindex_1 (dwz_out_file, dwz_cu_list, {}, {}, {}, {}, {});
else
gdb_assert (dwz_cu_list.empty ());
}
@@ -88,6 +88,9 @@ struct mapped_gdb_index final : public mapped_index_base
/* A pointer to the constant pool. */
gdb::array_view<const gdb_byte> constant_pool;
+ /* The shortcut table data. */
+ gdb::array_view<const gdb_byte> shortcut_table;
+
/* Return the index into the constant pool of the name of the IDXth
symbol in the symbol table. */
offset_type symbol_name_index (offset_type idx) const
@@ -166,6 +169,7 @@ dwarf2_gdb_index::dump (struct objfile *objfile)
mapped_gdb_index *index = (gdb::checked_static_cast<mapped_gdb_index *>
(per_objfile->per_bfd->index_table.get ()));
+
gdb_printf (".gdb_index: version %d\n", index->version);
gdb_printf ("\n");
}
@@ -583,7 +587,7 @@ to use the section anyway."),
/* Indexes with higher version than the one supported by GDB may be no
longer backward compatible. */
- if (version > 8)
+ if (version > 9)
return 0;
map->version = version;
@@ -608,8 +612,17 @@ to use the section anyway."),
map->symbol_table
= offset_view (gdb::array_view<const gdb_byte> (symbol_table,
symbol_table_end));
-
++i;
+
+ if (version >= 9)
+ {
+ const gdb_byte *shortcut_table = addr + metadata[i];
+ const gdb_byte *shortcut_table_end = addr + metadata[i + 1];
+ map->shortcut_table
+ = gdb::array_view<const gdb_byte> (shortcut_table, shortcut_table_end);
+ ++i;
+ }
+
map->constant_pool = buffer.slice (metadata[i]);
if (map->constant_pool.empty () && !map->symbol_table.empty ())
@@ -763,6 +776,43 @@ create_addrmap_from_gdb_index (dwarf2_per_objfile *per_objfile,
= new (&per_bfd->obstack) addrmap_fixed (&per_bfd->obstack, &mutable_map);
}
+/* Sets the name and language of the main function from the shortcut table. */
+
+static void
+set_main_name_from_gdb_index (dwarf2_per_objfile *per_objfile,
+ mapped_gdb_index *index)
+{
+ const auto expected_size = 4 + sizeof (offset_type);
+ if (index->shortcut_table.size () < expected_size)
+ /* The data in the section is not present, is corrupted or is in a version
+ * we don't know about. Regardless, we can't make use of it. */
+ return;
+
+ auto ptr = index->shortcut_table.data ();
+ const auto dw_lang = extract_unsigned_integer (ptr, 4, BFD_ENDIAN_LITTLE);
+ if (dw_lang >= DW_LANG_hi_user)
+ {
+ complaint (_(".gdb_index shortcut table has invalid main language %u"),
+ (unsigned) dw_lang);
+ return;
+ }
+ if (dw_lang == 0)
+ {
+ /* Don't bother if the language for the main symbol was not known or if
+ * there was no main symbol at all when the index was built. */
+ return;
+ }
+ ptr += 4;
+
+ const auto lang = dwarf_lang_to_enum_language (dw_lang);
+ const auto name_offset = extract_unsigned_integer (ptr,
+ sizeof (offset_type),
+ BFD_ENDIAN_LITTLE);
+ const auto name = (const char*) (index->constant_pool.data () + name_offset);
+
+ set_objfile_main_name (per_objfile->objfile, name, (enum language) lang);
+}
+
/* See read-gdb-index.h. */
int
@@ -848,6 +898,8 @@ dwarf2_read_gdb_index
create_addrmap_from_gdb_index (per_objfile, map.get ());
+ set_main_name_from_gdb_index (per_objfile, map.get ());
+
per_bfd->index_table = std::move (map);
per_bfd->quick_file_names_table =
create_quick_file_names_table (per_bfd->all_units.size ());
@@ -17745,7 +17745,9 @@ leb128_size (const gdb_byte *buf)
}
}
-static enum language
+/* Converts DWARF language names to GDB language names. */
+
+enum language
dwarf_lang_to_enum_language (unsigned int lang)
{
enum language language;
@@ -21661,6 +21663,7 @@ prepare_one_comp_unit (struct dwarf2_cu *cu, struct die_info *comp_unit_die,
/* Set the language we're debugging. */
attr = dwarf2_attr (comp_unit_die, DW_AT_language, cu);
enum language lang;
+ dwarf_source_language dw_lang = (dwarf_source_language)0;
if (cu->producer != nullptr
&& strstr (cu->producer, "IBM XL C for OpenCL") != NULL)
{
@@ -21669,18 +21672,24 @@ prepare_one_comp_unit (struct dwarf2_cu *cu, struct die_info *comp_unit_die,
language detection we fall back to the DW_AT_producer
string. */
lang = language_opencl;
+ dw_lang = DW_LANG_OpenCL;
}
else if (cu->producer != nullptr
&& strstr (cu->producer, "GNU Go ") != NULL)
{
/* Similar hack for Go. */
lang = language_go;
+ dw_lang = DW_LANG_Go;
}
else if (attr != nullptr)
- lang = dwarf_lang_to_enum_language (attr->constant_value (0));
+ {
+ lang = dwarf_lang_to_enum_language (attr->constant_value (0));
+ dw_lang = (dwarf_source_language)attr->constant_value (0);
+ }
else
lang = pretend_language;
+ cu->per_cu->dw_lang = dw_lang;
cu->language_defn = language_def (lang);
switch (comp_unit_die->tag)
@@ -245,6 +245,14 @@ struct dwarf2_per_cu_data
functions above. */
std::vector <dwarf2_per_cu_data *> *imported_symtabs = nullptr;
+ /* The original DW_LANG_* value of the CU, as provided to us by
+ * DW_AT_language. It is interesting to keep this value around in cases where
+ * we can't use the values from the language enum, as the mapping to them is
+ * lossy, and, while that is usually fine, things like the index have an
+ * understandable bias towards not exposing internal GDB structures to the
+ * outside world, and so prefer to use DWARF constants in their stead. */
+ dwarf_source_language dw_lang;
+
/* Return true of IMPORTED_SYMTABS is empty or not yet allocated. */
bool imported_symtabs_empty () const
{
@@ -755,6 +763,10 @@ struct dwarf2_per_objfile
std::unique_ptr<dwarf2_cu>> m_dwarf2_cus;
};
+/* Converts DWARF language names to GDB language names. */
+
+enum language dwarf_lang_to_enum_language (unsigned int lang);
+
/* Get the dwarf2_per_objfile associated to OBJFILE. */
dwarf2_per_objfile *get_dwarf2_per_objfile (struct objfile *objfile);