* [PATCH] [gdb/symtab] Fix off-by-one error in cooked_indexer::recurse
@ 2023-08-09 15:08 Tom de Vries
2023-08-10 16:11 ` Tom de Vries
2023-08-10 16:28 ` Tom Tromey
0 siblings, 2 replies; 3+ messages in thread
From: Tom de Vries @ 2023-08-09 15:08 UTC (permalink / raw)
To: gdb-patches; +Cc: Tom Tromey
Test-case gdb.dwarf2/pr13961.exp contains:
...
<1><25>: Abbrev Number: 8 (DW_TAG_class_type)
<26> DW_AT_specification: <0x2a>
<1><2a>: Abbrev Number: 2 (DW_TAG_class_type)
<2b> DW_AT_name : foo
<2f> DW_AT_byte_size : 4
<30> DW_AT_decl_file : 1
<31> DW_AT_decl_line : 1
<32> DW_AT_sibling : <0x44>
...
The DIE at 0x25 contains an intra-CU forward reference, and is deferred during
DIE indexing in the cooked_index, by adding it to m_deferred_entries.
The resulting cooked index entries are:
...
[12] ((cooked_index_entry *) 0x3dbbd00)
name: foo
canonical: foo
DWARF tag: DW_TAG_class_type
flags: 0x0 []
DIE offset: 0x25
parent: ((cooked_index_entry *) 0x3dbbca0) [foo]
[13] ((cooked_index_entry *) 0x3dbbca0)
name: foo
canonical: foo
DWARF tag: DW_TAG_class_type
flags: 0x0 []
DIE offset: 0x2a
parent: ((cooked_index_entry *) 0)
...
Notice that 0x2a is the parent of 0x25.
The parent field is documented as:
...
/* The parent entry. This is NULL for top-level entries.
Otherwise, it points to the parent entry, such as a namespace or
class. */
const cooked_index_entry *parent_entry;
...
so I'd expect no parent for 0x25.
The parent is set here in cooked_indexer::make_index:
...
for (const auto &entry : m_deferred_entries)
{
void *obj = m_die_range_map.find (entry.spec_offset);
cooked_index_entry *parent = static_cast<cooked_index_entry *> (obj);
m_index_storage->add (entry.die_offset, entry.tag, entry.flags,
entry.name, parent, m_per_cu);
}
...
and AFAICT, we store in m_die_range_map the parent of the respective
spec_offset DIE (though that's not clear from the comment describing it).
So, the root cause of this is that when we lookup the parent for DIE 0x25, we get
m_die_range_map.find (0x2a) == 0x2a.
This is an off-by-one error, fixed in cooked_indexer::recurse by:
...
- CORE_ADDR start = form_addr (parent_entry->die_offset,
+ CORE_ADDR start = form_addr (parent_entry->die_offset + 1,
...
which gives us:
...
[12] ((cooked_index_entry *) 0x41e21f0)
name: foo
canonical: foo
DWARF tag: DW_TAG_class_type
flags: 0x0 []
DIE offset: 0x25
parent: ((cooked_index_entry *) 0)
[13] ((cooked_index_entry *) 0x41e2190)
name: foo
canonical: foo
DWARF tag: DW_TAG_class_type
flags: 0x0 []
DIE offset: 0x2a
parent: ((cooked_index_entry *) 0)
...
Tested on x86_64-linux.
PR symtab/30739
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30739
---
gdb/dwarf2/read.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index dd4fac52ca8..a64f82bd24a 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -16477,7 +16477,9 @@ cooked_indexer::recurse (cutu_reader *reader,
if (parent_entry != nullptr)
{
- CORE_ADDR start = form_addr (parent_entry->die_offset,
+ /* Both start and end are inclusive, so use both "+ 1" and "- 1" to
+ limit the range to the children of parent_entry. */
+ CORE_ADDR start = form_addr (parent_entry->die_offset + 1,
reader->cu->per_cu->is_dwz);
CORE_ADDR end = form_addr (sect_offset (info_ptr - 1 - reader->buffer),
reader->cu->per_cu->is_dwz);
base-commit: 3cdc2d7e66ab6a48014dcd425c88cfd42a964321
--
2.35.3
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] [gdb/symtab] Fix off-by-one error in cooked_indexer::recurse
2023-08-09 15:08 [PATCH] [gdb/symtab] Fix off-by-one error in cooked_indexer::recurse Tom de Vries
@ 2023-08-10 16:11 ` Tom de Vries
2023-08-10 16:28 ` Tom Tromey
1 sibling, 0 replies; 3+ messages in thread
From: Tom de Vries @ 2023-08-10 16:11 UTC (permalink / raw)
To: gdb-patches; +Cc: Tom Tromey
On 8/9/23 17:08, Tom de Vries via Gdb-patches wrote:
> Test-case gdb.dwarf2/pr13961.exp contains:
> ...
> <1><25>: Abbrev Number: 8 (DW_TAG_class_type)
> <26> DW_AT_specification: <0x2a>
> <1><2a>: Abbrev Number: 2 (DW_TAG_class_type)
> <2b> DW_AT_name : foo
> <2f> DW_AT_byte_size : 4
> <30> DW_AT_decl_file : 1
> <31> DW_AT_decl_line : 1
> <32> DW_AT_sibling : <0x44>
> ...
>
> The DIE at 0x25 contains an intra-CU forward reference, and is deferred during
> DIE indexing in the cooked_index, by adding it to m_deferred_entries.
>
> The resulting cooked index entries are:
> ...
> [12] ((cooked_index_entry *) 0x3dbbd00)
> name: foo
> canonical: foo
> DWARF tag: DW_TAG_class_type
> flags: 0x0 []
> DIE offset: 0x25
> parent: ((cooked_index_entry *) 0x3dbbca0) [foo]
>
> [13] ((cooked_index_entry *) 0x3dbbca0)
> name: foo
> canonical: foo
> DWARF tag: DW_TAG_class_type
> flags: 0x0 []
> DIE offset: 0x2a
> parent: ((cooked_index_entry *) 0)
> ...
>
> Notice that 0x2a is the parent of 0x25.
>
> The parent field is documented as:
> ...
> /* The parent entry. This is NULL for top-level entries.
> Otherwise, it points to the parent entry, such as a namespace or
> class. */
> const cooked_index_entry *parent_entry;
> ...
> so I'd expect no parent for 0x25.
>
> The parent is set here in cooked_indexer::make_index:
> ...
> for (const auto &entry : m_deferred_entries)
> {
> void *obj = m_die_range_map.find (entry.spec_offset);
> cooked_index_entry *parent = static_cast<cooked_index_entry *> (obj);
> m_index_storage->add (entry.die_offset, entry.tag, entry.flags,
> entry.name, parent, m_per_cu);
> }
> ...
> and AFAICT, we store in m_die_range_map the parent of the respective
> spec_offset DIE (though that's not clear from the comment describing it).
>
> So, the root cause of this is that when we lookup the parent for DIE 0x25, we get
> m_die_range_map.find (0x2a) == 0x2a.
>
> This is an off-by-one error, fixed in cooked_indexer::recurse by:
> ...
> - CORE_ADDR start = form_addr (parent_entry->die_offset,
> + CORE_ADDR start = form_addr (parent_entry->die_offset + 1,
> ...
> which gives us:
> ...
> [12] ((cooked_index_entry *) 0x41e21f0)
> name: foo
> canonical: foo
> DWARF tag: DW_TAG_class_type
> flags: 0x0 []
> DIE offset: 0x25
> parent: ((cooked_index_entry *) 0)
>
> [13] ((cooked_index_entry *) 0x41e2190)
> name: foo
> canonical: foo
> DWARF tag: DW_TAG_class_type
> flags: 0x0 []
> DIE offset: 0x2a
> parent: ((cooked_index_entry *) 0)
> ...
>
> Tested on x86_64-linux.
>
I've submitted a v2 that includes a test-case, which required a
preliminary patch:
- [PATCH v2 1/2] [gdb/symtab] Dump qualified name of cooked_index_entry
https://sourceware.org/pipermail/gdb-patches/2023-August/201511.html
- [PATCH v2 2/2] [gdb/symtab] Fix off-by-one error in
cooked_indexer::recurse
https://sourceware.org/pipermail/gdb-patches/2023-August/201512.html
Thanks,
- Tom
> PR symtab/30739
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30739
> ---
> gdb/dwarf2/read.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
> index dd4fac52ca8..a64f82bd24a 100644
> --- a/gdb/dwarf2/read.c
> +++ b/gdb/dwarf2/read.c
> @@ -16477,7 +16477,9 @@ cooked_indexer::recurse (cutu_reader *reader,
>
> if (parent_entry != nullptr)
> {
> - CORE_ADDR start = form_addr (parent_entry->die_offset,
> + /* Both start and end are inclusive, so use both "+ 1" and "- 1" to
> + limit the range to the children of parent_entry. */
> + CORE_ADDR start = form_addr (parent_entry->die_offset + 1,
> reader->cu->per_cu->is_dwz);
> CORE_ADDR end = form_addr (sect_offset (info_ptr - 1 - reader->buffer),
> reader->cu->per_cu->is_dwz);
>
> base-commit: 3cdc2d7e66ab6a48014dcd425c88cfd42a964321
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] [gdb/symtab] Fix off-by-one error in cooked_indexer::recurse
2023-08-09 15:08 [PATCH] [gdb/symtab] Fix off-by-one error in cooked_indexer::recurse Tom de Vries
2023-08-10 16:11 ` Tom de Vries
@ 2023-08-10 16:28 ` Tom Tromey
1 sibling, 0 replies; 3+ messages in thread
From: Tom Tromey @ 2023-08-10 16:28 UTC (permalink / raw)
To: Tom de Vries via Gdb-patches; +Cc: Tom de Vries, Tom Tromey
>>>>> "Tom" == Tom de Vries via Gdb-patches <gdb-patches@sourceware.org> writes:
Tom> Test-case gdb.dwarf2/pr13961.exp contains:
Tom> ...
Tom> <1><25>: Abbrev Number: 8 (DW_TAG_class_type)
Tom> <26> DW_AT_specification: <0x2a>
Tom> <1><2a>: Abbrev Number: 2 (DW_TAG_class_type)
Tom> <2b> DW_AT_name : foo
Tom> <2f> DW_AT_byte_size : 4
Tom> <30> DW_AT_decl_file : 1
Tom> <31> DW_AT_decl_line : 1
Tom> <32> DW_AT_sibling : <0x44>
It took me a while to understand the problem here, but I get it now.
Thanks for doing this.
Approved-By: Tom Tromey <tom@tromey.com>
BTW this is maybe my least favorite part of DWARF, though the
competition is pretty tough.
Tom
^ permalink raw reply [flat|nested] 3+ messages in thread
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2023-08-09 15:08 [PATCH] [gdb/symtab] Fix off-by-one error in cooked_indexer::recurse Tom de Vries
2023-08-10 16:11 ` Tom de Vries
2023-08-10 16:28 ` Tom Tromey
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