Re: [PATCH 07/14] Add dwarf2_per_cu_data::index

Luis Machado
2020-02-18T11:39:06Z

On 2/15/20 1:54 PM, Tom Tromey wrote:
> Currently a dwarf2_per_cu_data can hold a link to the corresponding
> compunit_symtab. However, once these objects are shared across
> objfiles, a simple pointer won't work.
>
> Instead, this link will be stored in the dwarf2_unshareable object.
> To enable this, we add an index to each dwarf2_per_cu_data and
> signatured_type.
>
> 2020-02-15 Tom Tromey <tom@tromey.com>
>
> * dwarf2/read.h (struct dwarf2_per_objfile) <allocate_per_cu,
> allocate_signatured_type>: Declare new methods.
> (struct dwarf2_per_cu_data) <index>: New member.
> (struct dwarf2_per_objfile) <num_psymtabs>: New member.
> * dwarf2/read.c (dwarf2_per_objfile::allocate_per_cu)
> (dwarf2_per_objfile::allocate_signatured_type): New methods.
> (create_cu_from_index_list): Use allocate_per_cu.
> (create_signatured_type_table_from_index)
> (create_signatured_type_table_from_debug_names)
> (create_debug_type_hash_table, add_type_unit)
> (read_comp_units_from_section): Use allocate_signatured_type.
> ---
> gdb/ChangeLog | 14 +++++++++++++
> gdb/dwarf2/read.c | 52 +++++++++++++++++++++++++++--------------------
> gdb/dwarf2/read.h | 18 ++++++++++++++++
> 3 files changed, 62 insertions(+), 22 deletions(-)
>
> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
> index cb04eb19beb..281d39ad271 100644
> --- a/gdb/dwarf2/read.c
> +++ b/gdb/dwarf2/read.c
> @@ -2415,18 +2415,36 @@ dwarf2_per_objfile::get_tu (int index)
> return this->all_type_units[index];
> }
>
> +/* See read.h. */
> +
> +dwarf2_per_cu_data *
> +dwarf2_per_objfile::allocate_per_cu ()
> +{
> + dwarf2_per_cu_data *result = OBSTACK_ZALLOC (&obstack, dwarf2_per_cu_data);
> + result->index = num_psymtabs++;
> + return result;
> +}
> +
> +/* See read.h. */
> +
> +signatured_type *
> +dwarf2_per_objfile::allocate_signatured_type ()
> +{
> + signatured_type *result = OBSTACK_ZALLOC (&obstack, signatured_type);
> + result->per_cu.index = num_psymtabs++;
> + return result;
> +}
> +
> /* Return a new dwarf2_per_cu_data allocated on the dwarf2_per_objfile
> obstack, and constructed with the specified field values. */
>
> static dwarf2_per_cu_data *
> create_cu_from_index_list (struct dwarf2_per_objfile *dwarf2_per_objfile,
> - struct dwarf2_section_info *section,
> - int is_dwz,
> - sect_offset sect_off, ULONGEST length)
> + struct dwarf2_section_info *section,
> + int is_dwz,
> + sect_offset sect_off, ULONGEST length)

Did only formatting change above?

> {
> - dwarf2_per_cu_data *the_cu
> - = OBSTACK_ZALLOC (&dwarf2_per_objfile->obstack,
> - struct dwarf2_per_cu_data);
> + dwarf2_per_cu_data *the_cu = dwarf2_per_objfile->allocate_per_cu ();
> the_cu->sect_off = sect_off;
> the_cu->length = length;
> the_cu->dwarf2_per_objfile = dwarf2_per_objfile;
> @@ -2517,8 +2535,7 @@ create_signatured_type_table_from_index
> signature = extract_unsigned_integer (bytes + 16, 8, BFD_ENDIAN_LITTLE);
> bytes += 3 * 8;
>
> - sig_type = OBSTACK_ZALLOC (&dwarf2_per_objfile->obstack,
> - struct signatured_type);
> + sig_type = dwarf2_per_objfile->allocate_signatured_type ();
> sig_type->signature = signature;
> sig_type->type_offset_in_tu = type_offset_in_tu;
> sig_type->per_cu.is_debug_types = 1;
> @@ -2574,8 +2591,7 @@ create_signatured_type_table_from_debug_names
> section->buffer + to_underlying (sect_off),
> rcuh_kind::TYPE);
>
> - sig_type = OBSTACK_ZALLOC (&dwarf2_per_objfile->obstack,
> - struct signatured_type);
> + sig_type = dwarf2_per_objfile->allocate_signatured_type ();
> sig_type->signature = cu_header.signature;
> sig_type->type_offset_in_tu = cu_header.type_cu_offset_in_tu;
> sig_type->per_cu.is_debug_types = 1;
> @@ -6091,8 +6107,7 @@ create_debug_type_hash_table (struct dwarf2_per_objfile *dwarf2_per_objfile,
> /* N.B.: type_offset is not usable if this type uses a DWO file.
> The real type_offset is in the DWO file. */
> dwo_tu = NULL;
> - sig_type = OBSTACK_ZALLOC (&dwarf2_per_objfile->obstack,
> - struct signatured_type);
> + sig_type = dwarf2_per_objfile->allocate_signatured_type ();
> sig_type->signature = header.signature;
> sig_type->type_offset_in_tu = header.type_cu_offset_in_tu;
> sig_type->per_cu.dwarf2_per_objfile = dwarf2_per_objfile;
> @@ -6207,8 +6222,7 @@ add_type_unit (struct dwarf2_per_objfile *dwarf2_per_objfile, ULONGEST sig,
> == dwarf2_per_objfile->all_type_units.capacity ())
> ++dwarf2_per_objfile->tu_stats.nr_all_type_units_reallocs;
>
> - signatured_type *sig_type = OBSTACK_ZALLOC (&dwarf2_per_objfile->obstack,
> - struct signatured_type);
> + signatured_type *sig_type = dwarf2_per_objfile->allocate_signatured_type ();
>
> dwarf2_per_objfile->all_type_units.push_back (sig_type);
> sig_type->signature = sig;
> @@ -7835,16 +7849,10 @@ read_comp_units_from_section (struct dwarf2_per_objfile *dwarf2_per_objfile,
>
> /* Save the compilation unit for later lookup. */
> if (cu_header.unit_type != DW_UT_type)
> - {
> - this_cu = XOBNEW (&dwarf2_per_objfile->obstack,
> - struct dwarf2_per_cu_data);
> - memset (this_cu, 0, sizeof (*this_cu));
> - }
> + this_cu = dwarf2_per_objfile->allocate_per_cu ();
> else
> {
> - auto sig_type = XOBNEW (&dwarf2_per_objfile->obstack,
> - struct signatured_type);
> - memset (sig_type, 0, sizeof (*sig_type));
> + auto sig_type = dwarf2_per_objfile->allocate_signatured_type ();
> sig_type->signature = cu_header.signature;
> sig_type->type_offset_in_tu = cu_header.type_cu_offset_in_tu;
> this_cu = &sig_type->per_cu;
> diff --git a/gdb/dwarf2/read.h b/gdb/dwarf2/read.h
> index 06a0fa3a19a..5fc7f7f72e5 100644
> --- a/gdb/dwarf2/read.h
> +++ b/gdb/dwarf2/read.h
> @@ -128,6 +128,17 @@ struct dwarf2_per_objfile
>
> /* Free all cached compilation units. */
> void free_cached_comp_units ();
> +
> + /* A convenience function to allocate a dwarf2_per_cu_data (or
> + object holding one, using C-style derivation). The returned
> + object has its "index" field set properly. The object is
> + allocated on the dwarf2_per_objfile obstack. FIXME the index
> + here is weird since it may not (!?!?) be the same as the other
> + index */

I'm a bit lost on the above comment. Instead of having a FIXME here, is
there something we can do better at this point? Or maybe it will be
addressed later in the series?

I couldn't quite understand the problems with the indexes, but you're
more familiar with the DWARF reading code than i am.

> + dwarf2_per_cu_data *allocate_per_cu ();
> +
> + signatured_type *allocate_signatured_type ();
> +
> private:
> /* This function is mapped across the sections and remembers the
> offset and size of each of the debugging sections we are
> @@ -255,6 +266,10 @@ public:
> /* CUs that are queued to be read. */
> std::queue<dwarf2_queue_item> queue;
>
> + /* The total number of per_cu and signatured_type objects that have
> + been created for this reader. */
> + size_t num_psymtabs = 0;
> +
> /* State that cannot be shared across objfiles. This is normally
> nullptr and is temporarily set to the correct value at the entry
> points of the reader. */
> @@ -336,6 +351,9 @@ struct dwarf2_per_cu_data
> This flag is only valid if is_debug_types is true. */
> unsigned int tu_read : 1;
>
> + /* Our index in the unshared "all_cutus" vector. */
> + unsigned index;
> +

What is the all_cutus vector? I don't see it being added later in the
series. Should we make it more clear? Maybe you meant "all CU's/TU's"?

> /* The section this CU/TU lives in.
> If the DIE refers to a DWO file, this is always the original die,
> not the DWO file. */
>