[PATCH 05/14] Introduce dwarf2_unshareable and move die_type_hash

Tom Tromey
2020-02-15T16:54:51Z

The goal of this series is to share dwarf2_per_objfile across
objfiles. However, this is difficult to do, because it has some
members that are inherently per-objfile.

This patch introduces a new "unshareable" object. The idea here is
that we'll have one such object per objfile, and we'll temporarily
update the pointer when needed. This is a bit ugly, but it's
convenient, because it doesn't require a huge rewriting of the DWARF
code. (I would be in favor of such a rewriting, but ... it's huge.)

This patch further moves one such member, the DIE type hash, to the
new structure.

In this patch, the new object is managed by the dwarf2_per_objfile.
However, by the end of the series, this will change.

gdb/ChangeLog
2020-02-15 Tom Tromey <tom@tromey.com>

* dwarf2/read.h (struct dwarf2_unshareable): New type.
(struct dwarf2_per_objfile) <die_type_hash>: Move to
dwarf2_unshareable.
<unshareable>: New member.
* dwarf2/read.c (dwarf2_per_objfile::dwarf2_per_objfile):
Initialize "unshareable".
(dwarf2_per_objfile::~dwarf2_per_objfile): Delete unshareable.
(set_die_type, get_die_type_at_offset): Update.
---
gdb/ChangeLog | 11 +++++++++++
gdb/dwarf2/read.c | 19 +++++++++++++------
gdb/dwarf2/read.h | 28 +++++++++++++++++++++++-----
3 files changed, 47 insertions(+), 11 deletions(-)

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index a897b11693a..cb04eb19beb 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -1774,7 +1774,10 @@ dwarf2_per_objfile::dwarf2_per_objfile (struct objfile *objfile_,
const dwarf2_debug_sections *names,
bool can_copy_)
: objfile (objfile_),
- can_copy (can_copy_)
+ can_copy (can_copy_),
+ /* Temporarily just allocate one per objfile -- we don't have
+ sharing yet. */
+ unshareable (new dwarf2_unshareable)
{
if (names == NULL)
names = &dwarf2_elf_names;
@@ -1796,6 +1799,8 @@ dwarf2_per_objfile::~dwarf2_per_objfile ()
for (signatured_type *sig_type : all_type_units)
sig_type->per_cu.imported_symtabs_free ();

+ delete unshareable;
+
/* Everything else should be on the objfile obstack. */
}

@@ -24434,8 +24439,8 @@ set_die_type (struct die_info *die, struct type *type, struct dwarf2_cu *cu)
cu->per_cu->addr_type ()))
add_dyn_prop (DYN_PROP_DATA_LOCATION, prop, type);

- if (dwarf2_per_objfile->die_type_hash == NULL)
- dwarf2_per_objfile->die_type_hash
+ if (dwarf2_per_objfile->unshareable->die_type_hash == NULL)
+ dwarf2_per_objfile->unshareable->die_type_hash
= htab_up (htab_create_alloc (127,
per_cu_offset_and_type_hash,
per_cu_offset_and_type_eq,
@@ -24445,7 +24450,8 @@ set_die_type (struct die_info *die, struct type *type, struct dwarf2_cu *cu)
ofs.sect_off = die->sect_off;
ofs.type = type;
slot = (struct dwarf2_per_cu_offset_and_type **)
- htab_find_slot (dwarf2_per_objfile->die_type_hash.get (), &ofs, INSERT);
+ htab_find_slot (dwarf2_per_objfile->unshareable->die_type_hash.get (),
+ &ofs, INSERT);
if (*slot)
complaint (_("A problem internal to GDB: DIE %s has type already set"),
sect_offset_str (die->sect_off));
@@ -24465,13 +24471,14 @@ get_die_type_at_offset (sect_offset sect_off,
struct dwarf2_per_cu_offset_and_type *slot, ofs;
struct dwarf2_per_objfile *dwarf2_per_objfile = per_cu->dwarf2_per_objfile;

- if (dwarf2_per_objfile->die_type_hash == NULL)
+ if (dwarf2_per_objfile->unshareable->die_type_hash == NULL)
return NULL;

ofs.per_cu = per_cu;
ofs.sect_off = sect_off;
slot = ((struct dwarf2_per_cu_offset_and_type *)
- htab_find (dwarf2_per_objfile->die_type_hash.get (), &ofs));
+ htab_find (dwarf2_per_objfile->unshareable->die_type_hash.get (),
+ &ofs));
if (slot)
return slot->type;
else
diff --git a/gdb/dwarf2/read.h b/gdb/dwarf2/read.h
index 5fa8dec9bfb..06a0fa3a19a 100644
--- a/gdb/dwarf2/read.h
+++ b/gdb/dwarf2/read.h
@@ -66,6 +66,24 @@ struct dwarf2_queue_item
enum language pretend_language;
};

+/* Some DWARF data cannot (currently) be shared across objfiles. Such
+ data is stored in this object.
+
+ dwarf2_per_objfile holds a pointer to an instance of this object.
+ This pointer is temporarily set when expanding CUs. This hackish
+ approach is due to the history of the DWARF reader. In the past,
+ all objects were stored per-objfile, and this object was introduced
+ in the process of separating out the shareable and per-objfile
+ state. */
+
+struct dwarf2_unshareable
+{
+ /* Table mapping type DIEs to their struct type *.
+ This is NULL if not allocated yet.
+ The mapping is done via (CU/TU + DIE offset) -> type. */
+ htab_up die_type_hash;
+};
+
/* Collection of data recorded per objfile.
This hangs off of dwarf2_objfile_data_key. */

@@ -214,11 +232,6 @@ public:
symbols. */
bool reading_partial_symbols = false;

- /* Table mapping type DIEs to their struct type *.
- This is NULL if not allocated yet.
- The mapping is done via (CU/TU + DIE offset) -> type. */
- htab_up die_type_hash;
-
/* The CUs we recently read. */
std::vector<dwarf2_per_cu_data *> just_read_cus;

@@ -241,6 +254,11 @@ public:

/* CUs that are queued to be read. */
std::queue<dwarf2_queue_item> queue;
+
+ /* 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. */
+ dwarf2_unshareable *unshareable = nullptr;
};

/* Get the dwarf2_per_objfile associated to OBJFILE. */
--
2.17.2