Re: [PATCH v2 39/42] Pass existing_cu object to cutu_reader

Simon Marchi
2020-05-25T19:10:08Z

On 2020-05-22 4:57 p.m., Tom Tromey wrote:
>>>>>> "Simon" == Simon Marchi via Gdb-patches <gdb-patches@sourceware.org> writes:
>
> Simon> It is possible, seemingly for a special case described in
> Simon> find_partial_die, for cutu_reader to re-use an existing dwarf2_cu
> Simon> instead of creating a new one. This happens
> Simon> ---
>
> The description got cut off here, and there's no ChangeLog entry.
>
> Tom
>

Oops, I messed up, not sure what happened.

Here's the full version:

From 3d20153d73373a0c2281d2dd9a6ffe505f6346bc Mon Sep 17 00:00:00 2001
From: Simon Marchi <simon.marchi@efficios.com>
Date: Thu, 9 Apr 2020 13:46:41 -0400
Subject: [PATCH] Pass existing_cu object to cutu_reader

It is possible, seemingly for a special case described in
find_partial_die, for cutu_reader to re-use an existing dwarf2_cu
instead of creating a new one. This happens when running this test, for
example:

make check TESTS="gdb.dwarf2/fission-reread.exp"

Right now the, `use_existing_cu` flag tells cutu_reader to use the
dwarf2_cu object at dwarf2_per_cu_data::cu. However, we'll remove that
field, so we need to find another solution.

This situation arises when some caller up the stack has already created
the dwarf2_cu to read a dwarf2_per_cu_data, but needs to re-read it with
some other parameters. Therefore, it's possible to just have that
caller pass down the dwarf2_cu object to use as a `existing_cu`
parameter. If `existing_cu` is NULL, it tells cutu_reader that it needs
to instantiate a new one.

gdb/ChangeLog:

* dwarf2/read.c (class cutu_reader) <cutu_reader>: Replace
`int use_existing_cu` parameter with `dwarf2_cu *existing_cu`.
(init_tu_and_read_dwo_dies): Likewise.
(cutu_reader::init_tu_and_read_dwo_dies): Likewise.
(cutu_reader::cutu_reader): Likewise.
(load_partial_comp_unit): Likewise.
(process_psymtab_comp_unit): Update.
(build_type_psymtabs_1): Update.
(process_skeletonless_type_unit): Update.
(load_full_comp_unit): Update.
(find_partial_die): Update.
(dwarf2_read_addr_index): Update.
(read_signatured_type): Update.
---
gdb/dwarf2/read.c | 57 ++++++++++++++++++++++++++---------------------
1 file changed, 32 insertions(+), 25 deletions(-)

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index a6b7f2c6d25..c2dc34477f7 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -912,7 +912,7 @@ class cutu_reader : public die_reader_specs
cutu_reader (dwarf2_per_cu_data *this_cu,
dwarf2_per_objfile *per_objfile,
struct abbrev_table *abbrev_table,
- int use_existing_cu,
+ dwarf2_cu *existing_cu,
bool skip_partial);

explicit cutu_reader (struct dwarf2_per_cu_data *this_cu,
@@ -933,7 +933,7 @@ class cutu_reader : public die_reader_specs
private:
void init_tu_and_read_dwo_dies (dwarf2_per_cu_data *this_cu,
dwarf2_per_objfile *per_objfile,
- int use_existing_cu);
+ dwarf2_cu *existing_cu);

struct dwarf2_per_cu_data *m_this_cu;
std::unique_ptr<dwarf2_cu> m_new_cu;
@@ -6902,7 +6902,7 @@ lookup_dwo_unit (dwarf2_cu *cu, die_info *comp_unit_die, const char *dwo_name)
void
cutu_reader::init_tu_and_read_dwo_dies (dwarf2_per_cu_data *this_cu,
dwarf2_per_objfile *per_objfile,
- int use_existing_cu)
+ dwarf2_cu *existing_cu)
{
struct signatured_type *sig_type;

@@ -6912,24 +6912,28 @@ cutu_reader::init_tu_and_read_dwo_dies (dwarf2_per_cu_data *this_cu,
sig_type = (struct signatured_type *) this_cu;
gdb_assert (sig_type->dwo_unit != NULL);

- if (use_existing_cu && this_cu->cu != NULL)
+ dwarf2_cu *cu;
+
+ if (existing_cu != nullptr)
{
- gdb_assert (this_cu->cu->dwo_unit == sig_type->dwo_unit);
+ cu = existing_cu;
+ gdb_assert (cu->dwo_unit == sig_type->dwo_unit);
/* There's no need to do the rereading_dwo_cu handling that
cutu_reader does since we don't read the stub. */
}
else
{
- /* If !use_existing_cu, this_cu->cu must be NULL. */
+ /* If an existing_cu is provided, this_cu->cu must be NULL. */
gdb_assert (this_cu->cu == NULL);
m_new_cu.reset (new dwarf2_cu (this_cu, per_objfile));
+ cu = m_new_cu.get ();
}

/* A future optimization, if needed, would be to use an existing
abbrev table. When reading DWOs with skeletonless TUs, all the TUs
could share abbrev tables. */

- if (read_cutu_die_from_dwo (this_cu->cu, sig_type->dwo_unit,
+ if (read_cutu_die_from_dwo (cu, sig_type->dwo_unit,
NULL /* stub_comp_unit_die */,
sig_type->dwo_unit->dwo_file->comp_dir,
this, &info_ptr,
@@ -6948,13 +6952,13 @@ cutu_reader::init_tu_and_read_dwo_dies (dwarf2_per_cu_data *this_cu,
Otherwise the table specified in the comp unit header is read in and used.
This is an optimization for when we already have the abbrev table.

- If USE_EXISTING_CU is non-zero, and THIS_CU->cu is non-NULL, then use it.
- Otherwise, a new CU is allocated with xmalloc. */
+ If EXISTING_CU is non-NULL, then use it. Otherwise, a new CU is
+ allocated. */

cutu_reader::cutu_reader (dwarf2_per_cu_data *this_cu,
dwarf2_per_objfile *dwarf2_per_objfile,
struct abbrev_table *abbrev_table,
- int use_existing_cu,
+ dwarf2_cu *existing_cu,
bool skip_partial)
: die_reader_specs {},
m_this_cu (this_cu)
@@ -6962,7 +6966,6 @@ cutu_reader::cutu_reader (dwarf2_per_cu_data *this_cu,
struct objfile *objfile = dwarf2_per_objfile->objfile;
struct dwarf2_section_info *section = this_cu->section;
bfd *abfd = section->get_bfd_owner ();
- struct dwarf2_cu *cu;
const gdb_byte *begin_info_ptr;
struct signatured_type *sig_type = NULL;
struct dwarf2_section_info *abbrev_section;
@@ -6983,7 +6986,7 @@ cutu_reader::cutu_reader (dwarf2_per_cu_data *this_cu,
/* Narrow down the scope of possibilities to have to understand. */
gdb_assert (this_cu->is_debug_types);
gdb_assert (abbrev_table == NULL);
- init_tu_and_read_dwo_dies (this_cu, dwarf2_per_objfile, use_existing_cu);
+ init_tu_and_read_dwo_dies (this_cu, dwarf2_per_objfile, existing_cu);
return;
}

@@ -6994,9 +6997,11 @@ cutu_reader::cutu_reader (dwarf2_per_cu_data *this_cu,

abbrev_section = get_abbrev_section_for_cu (this_cu);

- if (use_existing_cu && this_cu->cu != NULL)
+ dwarf2_cu *cu;
+
+ if (existing_cu != nullptr)
{
- cu = this_cu->cu;
+ cu = existing_cu;
/* If this CU is from a DWO file we need to start over, we need to
refetch the attributes from the skeleton CU.
This could be optimized by retrieving those attributes from when we
@@ -7008,7 +7013,7 @@ cutu_reader::cutu_reader (dwarf2_per_cu_data *this_cu,
}
else
{
- /* If !use_existing_cu, this_cu->cu must be NULL. */
+ /* If an existing_cu is provided, this_cu->cu must be NULL. */
gdb_assert (this_cu->cu == NULL);
m_new_cu.reset (new dwarf2_cu (this_cu, dwarf2_per_objfile));
cu = m_new_cu.get ();
@@ -7561,7 +7566,7 @@ process_psymtab_comp_unit (dwarf2_per_cu_data *this_cu,
if (this_cu->cu != NULL)
free_one_cached_comp_unit (this_cu, per_objfile);

- cutu_reader reader (this_cu, per_objfile, NULL, 0, false);
+ cutu_reader reader (this_cu, per_objfile, nullptr, nullptr, false);

switch (reader.comp_unit_die->tag)
{
@@ -7743,7 +7748,7 @@ build_type_psymtabs_1 (struct dwarf2_per_objfile *dwarf2_per_objfile)
}

cutu_reader reader (&tu.sig_type->per_cu, dwarf2_per_objfile,
- abbrev_table.get (), 0, false);
+ abbrev_table.get (), nullptr, false);
if (!reader.dummy_p)
build_type_psymtabs_reader (&reader, reader.info_ptr,
reader.comp_unit_die);
@@ -7848,7 +7853,8 @@ process_skeletonless_type_unit (void **slot, void *info)
*slot = entry;

/* This does the job that build_type_psymtabs_1 would have done. */
- cutu_reader reader (&entry->per_cu, dwarf2_per_objfile, NULL, 0, false);
+ cutu_reader reader (&entry->per_cu, dwarf2_per_objfile, nullptr, nullptr,
+ false);
if (!reader.dummy_p)
build_type_psymtabs_reader (&reader, reader.info_ptr,
reader.comp_unit_die);
@@ -7984,9 +7990,10 @@ dwarf2_build_psymtabs_hard (struct dwarf2_per_objfile *dwarf2_per_objfile)

static void
load_partial_comp_unit (dwarf2_per_cu_data *this_cu,
- dwarf2_per_objfile *per_objfile)
+ dwarf2_per_objfile *per_objfile,
+ dwarf2_cu *existing_cu)
{
- cutu_reader reader (this_cu, per_objfile, NULL, 1, false);
+ cutu_reader reader (this_cu, per_objfile, nullptr, existing_cu, false);

if (!reader.dummy_p)
{
@@ -9105,7 +9112,7 @@ load_full_comp_unit (dwarf2_per_cu_data *this_cu,
{
gdb_assert (! this_cu->is_debug_types);

- cutu_reader reader (this_cu, per_objfile, NULL, 1, skip_partial);
+ cutu_reader reader (this_cu, per_objfile, NULL, this_cu->cu, skip_partial);
if (reader.dummy_p)
return;

@@ -18713,7 +18720,7 @@ find_partial_die (sect_offset sect_off, int offset_in_dwz, struct dwarf2_cu *cu)
dwarf2_per_objfile);

if (per_cu->cu == NULL || per_cu->cu->partial_dies == NULL)
- load_partial_comp_unit (per_cu, cu->per_objfile);
+ load_partial_comp_unit (per_cu, cu->per_objfile, nullptr);

per_cu->cu->last_used = 0;
pd = per_cu->cu->find_partial_die (sect_off);
@@ -18732,7 +18739,7 @@ find_partial_die (sect_offset sect_off, int offset_in_dwz, struct dwarf2_cu *cu)
DIEs alone (which can still be in use, e.g. in scan_partial_symbols),
and clobber THIS_CU->cu->partial_dies with the hash table for the new
set. */
- load_partial_comp_unit (per_cu, cu->per_objfile);
+ load_partial_comp_unit (per_cu, cu->per_objfile, cu);

pd = per_cu->cu->find_partial_die (sect_off);
}
@@ -19449,7 +19456,7 @@ dwarf2_read_addr_index (dwarf2_per_cu_data *per_cu,
}
else
{
- cutu_reader reader (per_cu, dwarf2_per_objfile, NULL, 0, false);
+ cutu_reader reader (per_cu, dwarf2_per_objfile, nullptr, nullptr, false);
addr_base = reader.cu->addr_base;
addr_size = reader.cu->header.addr_size;
}
@@ -22831,7 +22838,7 @@ read_signatured_type (signatured_type *sig_type,
gdb_assert (per_cu->is_debug_types);
gdb_assert (per_cu->cu == NULL);

- cutu_reader reader (per_cu, per_objfile, NULL, 0, false);
+ cutu_reader reader (per_cu, per_objfile, nullptr, nullptr, false);

if (!reader.dummy_p)
{
--
2.26.2