possible fix for PR symtab/23010

Tom Tromey
2018-04-12T19:06:08Z

I was talking with Keith & Pedro about PR symtab/23010 on irc this week,
because it was the bug at the base of the Rust -readnow problem that Jan
reported.

I came up with this patch yesterday. It fixes the problem, but I didn't
write a test and also I'm not sure if it is the best way to go.

So, I thought I'd send it for commentary.

Tom

commit bc5411ff15de7e207bfb80a42790adb5d6f80852
Author: Tom Tromey <tom@tromey.com>
Date: Thu Apr 12 08:24:41 2018 -0600

Fix for dwz-related crash

PR symtab/23010 reports a crash that occurs when using -readnow
on a dwz-generated debuginfo file.

The crash occurs because the DWARF has a partial CU with no language
set, and then a full CU that references this partial CU using
DW_AT_abstract_origin.

In this case, the partial CU is read by dw2_expand_all_symtabs using
language_minimal; but then this conflicts with the creation of the
block's symbol table in the C++ CU.

This patch fixes the problem by arranging for partial CUs not to be
read by -readnow. I tend to think that it doesn't make sense to read
a partial CU in isolation -- they should only be read when imported
into some other CU.

In conjunction with some other patches I am going to post, this also
fixes the Rust -readnow crash that Jan reported.

There are two problems with this patch:

1. It is difficult to reason about. There are many cases where I've
patched the code to call init_cutu_and_read_dies with the flag set
to "please do read partial units" -- but I find it difficult to be
sure that this is always correct.

2. It is still missing a standalone test case. This seemed hard.

2018-04-12 Tom Tromey <tom@tromey.com>

PR symtab/23010:
* dwarf2read.c (load_cu, dw2_do_instantiate_symtab)
(dw2_instantiate_symtab): Add skip_partial parameter.
(dw2_find_last_source_symtab, dw2_map_expand_apply)
(dw2_lookup_symbol, dw2_expand_symtabs_for_function)
(dw2_expand_all_symtabs, dw2_expand_symtabs_with_fullname)
(dw2_expand_symtabs_matching_one)
(dw2_find_pc_sect_compunit_symtab)
(dw2_debug_names_lookup_symbol)
(dw2_debug_names_expand_symtabs_for_function): Update.
(init_cutu_and_read_dies): Add skip_partial parameter.
(process_psymtab_comp_unit, build_type_psymtabs_1)
(process_skeletonless_type_unit, load_partial_comp_unit)
(psymtab_to_symtab_1): Update.
(load_full_comp_unit): Add skip_partial parameter.
(process_imported_unit_die, dwarf2_read_addr_index)
(follow_die_offset, dwarf2_fetch_die_loc_sect_off)
(dwarf2_fetch_constant_bytes, dwarf2_fetch_die_type_sect_off)
(read_signatured_type): Update.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index f2bb3d0af3..46e3c9d6cd 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,27 @@
2018-04-12 Tom Tromey <tom@tromey.com>

+ PR symtab/23010:
+ * dwarf2read.c (load_cu, dw2_do_instantiate_symtab)
+ (dw2_instantiate_symtab): Add skip_partial parameter.
+ (dw2_find_last_source_symtab, dw2_map_expand_apply)
+ (dw2_lookup_symbol, dw2_expand_symtabs_for_function)
+ (dw2_expand_all_symtabs, dw2_expand_symtabs_with_fullname)
+ (dw2_expand_symtabs_matching_one)
+ (dw2_find_pc_sect_compunit_symtab)
+ (dw2_debug_names_lookup_symbol)
+ (dw2_debug_names_expand_symtabs_for_function): Update.
+ (init_cutu_and_read_dies): Add skip_partial parameter.
+ (process_psymtab_comp_unit, build_type_psymtabs_1)
+ (process_skeletonless_type_unit, load_partial_comp_unit)
+ (psymtab_to_symtab_1): Update.
+ (load_full_comp_unit): Add skip_partial parameter.
+ (process_imported_unit_die, dwarf2_read_addr_index)
+ (follow_die_offset, dwarf2_fetch_die_loc_sect_off)
+ (dwarf2_fetch_constant_bytes, dwarf2_fetch_die_type_sect_off)
+ (read_signatured_type): Update.
+
+2018-04-12 Tom Tromey <tom@tromey.com>
+
* dwarf2read.c (read_structure_type): Set TYPE_NAME for rust
unions.

diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index e3f544a6a4..406aa0d52e 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -1832,7 +1832,7 @@ static void create_all_comp_units (struct dwarf2_per_objfile *dwarf2_per_objfile

static int create_all_type_units (struct dwarf2_per_objfile *dwarf2_per_objfile);

-static void load_full_comp_unit (struct dwarf2_per_cu_data *,
+static void load_full_comp_unit (struct dwarf2_per_cu_data *, bool,
enum language);

static void process_full_comp_unit (struct dwarf2_per_cu_data *,
@@ -1932,7 +1932,7 @@ static const gdb_byte *read_and_check_comp_unit_head

static void init_cutu_and_read_dies
(struct dwarf2_per_cu_data *this_cu, struct abbrev_table *abbrev_table,
- int use_existing_cu, int keep,
+ int use_existing_cu, int keep, bool skip_partial,
die_reader_func_ftype *die_reader_func, void *data);

static void init_cutu_and_read_dies_simple
@@ -2835,12 +2835,12 @@ create_quick_file_names_table (unsigned int nr_initial_entries)
processing PER_CU->CU. dw2_setup must have been already called. */

static void
-load_cu (struct dwarf2_per_cu_data *per_cu)
+load_cu (struct dwarf2_per_cu_data *per_cu, bool skip_partial)
{
if (per_cu->is_debug_types)
load_full_type_unit (per_cu);
else
- load_full_comp_unit (per_cu, language_minimal);
+ load_full_comp_unit (per_cu, skip_partial, language_minimal);

if (per_cu->cu == NULL)
return; /* Dummy CU. */
@@ -2851,7 +2851,7 @@ load_cu (struct dwarf2_per_cu_data *per_cu)
/* Read in the symbols for PER_CU. */

static void
-dw2_do_instantiate_symtab (struct dwarf2_per_cu_data *per_cu)
+dw2_do_instantiate_symtab (struct dwarf2_per_cu_data *per_cu, bool skip_partial)
{
struct dwarf2_per_objfile *dwarf2_per_objfile = per_cu->dwarf2_per_objfile;

@@ -2870,7 +2870,7 @@ dw2_do_instantiate_symtab (struct dwarf2_per_cu_data *per_cu)
: (per_cu->v.psymtab == NULL || !per_cu->v.psymtab->readin))
{
queue_comp_unit (per_cu, language_minimal);
- load_cu (per_cu);
+ load_cu (per_cu, true);

/* If we just loaded a CU from a DWO, and we're working with an index
that may badly handle TUs, load all the TUs in that DWO as well.
@@ -2897,7 +2897,7 @@ dw2_do_instantiate_symtab (struct dwarf2_per_cu_data *per_cu)
table. */

static struct compunit_symtab *
-dw2_instantiate_symtab (struct dwarf2_per_cu_data *per_cu)
+dw2_instantiate_symtab (struct dwarf2_per_cu_data *per_cu, bool skip_partial)
{
struct dwarf2_per_objfile *dwarf2_per_objfile = per_cu->dwarf2_per_objfile;

@@ -2906,7 +2906,7 @@ dw2_instantiate_symtab (struct dwarf2_per_cu_data *per_cu)
{
free_cached_comp_units freer (dwarf2_per_objfile);
scoped_restore decrementer = increment_reading_symtab ();
- dw2_do_instantiate_symtab (per_cu);
+ dw2_do_instantiate_symtab (per_cu, skip_partial);
process_cu_includes (dwarf2_per_objfile);
}

@@ -3741,7 +3741,7 @@ dw2_find_last_source_symtab (struct objfile *objfile)
struct dwarf2_per_objfile *dwarf2_per_objfile
= get_dwarf2_per_objfile (objfile);
dwarf2_per_cu_data *dwarf_cu = dwarf2_per_objfile->all_comp_units.back ();
- compunit_symtab *cust = dw2_instantiate_symtab (dwarf_cu);
+ compunit_symtab *cust = dw2_instantiate_symtab (dwarf_cu, false);

if (cust == NULL)
return NULL;
@@ -3797,7 +3797,7 @@ dw2_map_expand_apply (struct objfile *objfile,

/* This may expand more than one symtab, and we want to iterate over
all of them. */
- dw2_instantiate_symtab (per_cu);
+ dw2_instantiate_symtab (per_cu, false);

return iterate_over_some_symtabs (name, real_path, objfile->compunit_symtabs,
last_made, callback);
@@ -4037,7 +4037,7 @@ dw2_lookup_symbol (struct objfile *objfile, int block_index,
while ((per_cu = dw2_symtab_iter_next (&iter)) != NULL)
{
struct symbol *sym, *with_opaque = NULL;
- struct compunit_symtab *stab = dw2_instantiate_symtab (per_cu);
+ struct compunit_symtab *stab = dw2_instantiate_symtab (per_cu, false);
const struct blockvector *bv = COMPUNIT_BLOCKVECTOR (stab);
struct block *block = BLOCKVECTOR_BLOCK (bv, block_index);

@@ -4128,7 +4128,7 @@ dw2_expand_symtabs_for_function (struct objfile *objfile,
func_name);

while ((per_cu = dw2_symtab_iter_next (&iter)) != NULL)
- dw2_instantiate_symtab (per_cu);
+ dw2_instantiate_symtab (per_cu, false);

}

@@ -4144,7 +4144,7 @@ dw2_expand_all_symtabs (struct objfile *objfile)
{
dwarf2_per_cu_data *per_cu = dwarf2_per_objfile->get_cutu (i);

- dw2_instantiate_symtab (per_cu);
+ dw2_instantiate_symtab (per_cu, true);
}
}

@@ -4176,7 +4176,7 @@ dw2_expand_symtabs_with_fullname (struct objfile *objfile,

if (filename_cmp (this_fullname, fullname) == 0)
{
- dw2_instantiate_symtab (per_cu);
+ dw2_instantiate_symtab (per_cu, false);
break;
}
}
@@ -5000,7 +5000,7 @@ dw2_expand_symtabs_matching_one
bool symtab_was_null
= (per_cu->v.quick->compunit_symtab == NULL);

- dw2_instantiate_symtab (per_cu);
+ dw2_instantiate_symtab (per_cu, false);

if (expansion_notify != NULL
&& symtab_was_null
@@ -5250,7 +5250,8 @@ dw2_find_pc_sect_compunit_symtab (struct objfile *objfile,
paddress (get_objfile_arch (objfile), pc));

result
- = recursively_find_pc_sect_compunit_symtab (dw2_instantiate_symtab (data),
+ = recursively_find_pc_sect_compunit_symtab (dw2_instantiate_symtab (data,
+ false),
pc);
gdb_assert (result != NULL);
return result;
@@ -6049,7 +6050,7 @@ dw2_debug_names_lookup_symbol (struct objfile *objfile, int block_index_int,
while ((per_cu = iter.next ()) != NULL)
{
struct symbol *sym, *with_opaque = NULL;
- struct compunit_symtab *stab = dw2_instantiate_symtab (per_cu);
+ struct compunit_symtab *stab = dw2_instantiate_symtab (per_cu, false);
const struct blockvector *bv = COMPUNIT_BLOCKVECTOR (stab);
struct block *block = BLOCKVECTOR_BLOCK (bv, block_index);

@@ -6111,7 +6112,7 @@ dw2_debug_names_expand_symtabs_for_function (struct objfile *objfile,

struct dwarf2_per_cu_data *per_cu;
while ((per_cu = iter.next ()) != NULL)
- dw2_instantiate_symtab (per_cu);
+ dw2_instantiate_symtab (per_cu, false);
}
}

@@ -7410,6 +7411,7 @@ static void
init_cutu_and_read_dies (struct dwarf2_per_cu_data *this_cu,
struct abbrev_table *abbrev_table,
int use_existing_cu, int keep,
+ bool skip_partial,
die_reader_func_ftype *die_reader_func,
void *data)
{
@@ -7548,6 +7550,9 @@ init_cutu_and_read_dies (struct dwarf2_per_cu_data *this_cu,
init_cu_die_reader (&reader, cu, section, NULL, abbrev_table);
info_ptr = read_full_die (&reader, &comp_unit_die, info_ptr, &has_children);

+ if (skip_partial && comp_unit_die->tag == DW_TAG_partial_unit)
+ return;
+
/* If we are in a DWO stub, process it and then read in the "real" CU/TU
from the DWO file. read_cutu_die_from_dwo will allocate the abbreviation
table from the DWO file and pass the ownership over to us. It will be
@@ -8042,14 +8047,14 @@ process_psymtab_comp_unit (struct dwarf2_per_cu_data *this_cu,
free_one_cached_comp_unit (this_cu);

if (this_cu->is_debug_types)
- init_cutu_and_read_dies (this_cu, NULL, 0, 0, build_type_psymtabs_reader,
- NULL);
+ init_cutu_and_read_dies (this_cu, NULL, 0, 0, false,
+ build_type_psymtabs_reader, NULL);
else
{
process_psymtab_comp_unit_data info;
info.want_partial_unit = want_partial_unit;
info.pretend_language = pretend_language;
- init_cutu_and_read_dies (this_cu, NULL, 0, 0,
+ init_cutu_and_read_dies (this_cu, NULL, 0, 0, false,
process_psymtab_comp_unit_reader, &info);
}

@@ -8209,7 +8214,7 @@ build_type_psymtabs_1 (struct dwarf2_per_objfile *dwarf2_per_objfile)
}

init_cutu_and_read_dies (&tu.sig_type->per_cu, abbrev_table.get (),
- 0, 0, build_type_psymtabs_reader, NULL);
+ 0, 0, false, build_type_psymtabs_reader, NULL);
}
}

@@ -8316,7 +8321,7 @@ process_skeletonless_type_unit (void **slot, void *info)
*slot = entry;

/* This does the job that build_type_psymtabs_1 would have done. */
- init_cutu_and_read_dies (&entry->per_cu, NULL, 0, 0,
+ init_cutu_and_read_dies (&entry->per_cu, NULL, 0, 0, false,
build_type_psymtabs_reader, NULL);

return 1;
@@ -8464,7 +8469,7 @@ load_partial_comp_unit_reader (const struct die_reader_specs *reader,
static void
load_partial_comp_unit (struct dwarf2_per_cu_data *this_cu)
{
- init_cutu_and_read_dies (this_cu, NULL, 1, 1,
+ init_cutu_and_read_dies (this_cu, NULL, 1, 1, false,
load_partial_comp_unit_reader, NULL);
}

@@ -9558,7 +9563,7 @@ psymtab_to_symtab_1 (struct partial_symtab *pst)
return;
}

- dw2_do_instantiate_symtab (per_cu);
+ dw2_do_instantiate_symtab (per_cu, false);
}

/* Trivial hash function for die_info: the hash value of a DIE
@@ -9627,11 +9632,12 @@ load_full_comp_unit_reader (const struct die_reader_specs *reader,

static void
load_full_comp_unit (struct dwarf2_per_cu_data *this_cu,
+ bool skip_partial,
enum language pretend_language)
{
gdb_assert (! this_cu->is_debug_types);

- init_cutu_and_read_dies (this_cu, NULL, 1, 1,
+ init_cutu_and_read_dies (this_cu, NULL, 1, 1, skip_partial,
load_full_comp_unit_reader, &pretend_language);
}

@@ -10458,7 +10464,7 @@ process_imported_unit_die (struct die_info *die, struct dwarf2_cu *cu)

/* If necessary, add it to the queue and load its DIEs. */
if (maybe_queue_comp_unit (cu, per_cu, cu->language))
- load_full_comp_unit (per_cu, cu->language);
+ load_full_comp_unit (per_cu, false, cu->language);

VEC_safe_push (dwarf2_per_cu_ptr, cu->per_cu->imported_symtabs,
per_cu);
@@ -19569,7 +19575,7 @@ dwarf2_read_addr_index (struct dwarf2_per_cu_data *per_cu,

/* Note: We can't use init_cutu_and_read_dies_simple here,
we need addr_base. */
- init_cutu_and_read_dies (per_cu, NULL, 0, 0,
+ init_cutu_and_read_dies (per_cu, NULL, 0, 0, false,
dwarf2_read_addr_index_reader, &aidata);
addr_base = aidata.addr_base;
addr_size = aidata.addr_size;
@@ -22776,7 +22782,7 @@ follow_die_offset (sect_offset sect_off, int offset_in_dwz,

/* If necessary, add it to the queue and load its DIEs. */
if (maybe_queue_comp_unit (cu, per_cu, cu->language))
- load_full_comp_unit (per_cu, cu->language);
+ load_full_comp_unit (per_cu, false, cu->language);

target_cu = per_cu->cu;
}
@@ -22784,7 +22790,7 @@ follow_die_offset (sect_offset sect_off, int offset_in_dwz,
{
/* We're loading full DIEs during partial symbol reading. */
gdb_assert (dwarf2_per_objfile->reading_partial_symbols);
- load_full_comp_unit (cu->per_cu, language_minimal);
+ load_full_comp_unit (cu->per_cu, false, language_minimal);
}

*ref_cu = target_cu;
@@ -22838,7 +22844,7 @@ dwarf2_fetch_die_loc_sect_off (sect_offset sect_off,
struct objfile *objfile = dwarf2_per_objfile->objfile;

if (per_cu->cu == NULL)
- load_cu (per_cu);
+ load_cu (per_cu, false);
cu = per_cu->cu;
if (cu == NULL)
{
@@ -22945,7 +22951,7 @@ dwarf2_fetch_constant_bytes (sect_offset sect_off,
struct objfile *objfile = per_cu->dwarf2_per_objfile->objfile;

if (per_cu->cu == NULL)
- load_cu (per_cu);
+ load_cu (per_cu, false);
cu = per_cu->cu;
if (cu == NULL)
{
@@ -23067,7 +23073,7 @@ dwarf2_fetch_die_type_sect_off (sect_offset sect_off,
struct die_info *die;

if (per_cu->cu == NULL)
- load_cu (per_cu);
+ load_cu (per_cu, false);
cu = per_cu->cu;
if (!cu)
return NULL;
@@ -23348,7 +23354,7 @@ read_signatured_type (struct signatured_type *sig_type)
gdb_assert (per_cu->is_debug_types);
gdb_assert (per_cu->cu == NULL);

- init_cutu_and_read_dies (per_cu, NULL, 0, 1,
+ init_cutu_and_read_dies (per_cu, NULL, 0, 1, false,
read_signatured_type_reader, NULL);
sig_type->per_cu.tu_read = 1;
}