[Bug symtab/29106] New: new DWARF reader should de-duplicate functions

[Bug symtab/29106] New: new DWARF reader should de-duplicate functions

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29106

            Bug ID: 29106
           Summary: new DWARF reader should de-duplicate functions
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: symtab
          Assignee: unassigned at sourceware dot org
          Reporter: tromey at sourceware dot org
  Target Milestone: ---

In https://sourceware.org/pipermail/gdb-patches/2022-April/188400.html,
Pedro pointed out that, even with the patch in that thread,
the new DWARF reader still generates a larger index:

In the old indexer, with an index of a gdb from before the indexer rewrite, we
had:

 [369902] intrusive_list<inferior, intrusive_base_node<inferior> >::begin:
          9 [global, function]
          255 [global, function]

while in the new indexer, for the same function, we have:

 [369902] intrusive_list<inferior, intrusive_base_node<inferior> >::begin:
         9 [global, function]
         79 [global, function]
         165 [global, function]
         167 [global, function]
[ ... many more instances ... ]

I suspect this is due to the old handling of DW_AT_inline.
See https://sourceware.org/pipermail/gdb-patches/2022-April/188557.html

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[Bug symtab/29106] new DWARF reader should de-duplicate functions

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29106

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at sourceware dot org   |tromey at sourceware dot org

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[Bug symtab/29106] new DWARF reader should de-duplicate functions

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29106

--- Comment #1 from Tom Tromey <tromey at sourceware dot org> ---
In a follow-up email, Pedro said:

Hmm, inlines was my original suspicion, but seeing that setting a breakpoint at
"intrusive_list<inferior, intrusive_base_node<inferior> >::begin", even with
-readnow gives you 2 locations, same number of locations as entries in the old
index,
could it be that this is more about declarations vs definitions?  There's that
check for
has_pc_info or has_range_info too.


So this ought to be investigated.

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[Bug symtab/29106] new DWARF reader should de-duplicate functions

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29106

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |29366


Referenced Bugs:

https://sourceware.org/bugzilla/show_bug.cgi?id=29366
[Bug 29366] [meta] New DWARF indexer meta bug
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[Bug symtab/29106] new DWARF reader should de-duplicate functions

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29106

--- Comment #2 from Tom Tromey <tromey at sourceware dot org> ---
It does seem that the declarations end up in the symbol table.
In one CU, there's a concrete instance like:

 <1><28afba>: Abbrev Number: 40 (DW_TAG_subprogram)
    <28afbb>   DW_AT_specification: <0x27d5e2>

... pointing back at the method declaration.
Both the old and new gdb will emit an index entry for this.

However, in another CU, there's the same declaration but
with no concrete instance -- and here, the old gdb does
not emit an entry, but the new one does.

I suspect these declarations shouldn't be in the cooked index
at all.

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[Bug symtab/29106] new DWARF reader should de-duplicate functions

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29106

--- Comment #3 from Tom Tromey <tromey at sourceware dot org> ---
Further searching shows that the second CU in question has:

 <1><d94e58>: Abbrev Number: 24 (DW_TAG_subprogram)
    <d94e59>   DW_AT_specification: <0xd5c48b>
    <d94e5d>   DW_AT_object_pointer: <0xd94e77>
    <d94e61>   DW_AT_low_pc      : 0x0
    <d94e69>   DW_AT_high_pc     : 0x28
    <d94e71>   DW_AT_frame_base  : 1 byte block: 9c     (DW_OP_call_frame_cfa)
    <d94e73>   DW_AT_call_all_tail_calls: 1
    <d94e73>   DW_AT_sibling     : <0xd94e84>

The new index seems more correct to me, and in particular the
old gdb index does:

(gdb) break intrusive_list<inferior, intrusive_base_node<inferior> >::begin()
const
Breakpoint 1 at 0x4ac474: intrusive_list<inferior,
intrusive_base_node<inferior> >::begin() const. (4 locations)


Whereas with the new index we get:

(gdb) break intrusive_list<inferior, intrusive_base_node<inferior> >::begin()
const
Breakpoint 1 at 0x4ac474: intrusive_list<inferior,
intrusive_base_node<inferior> >::begin() const. (58 locations)

So I tend to think the old gdb was missing some locations.

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[Bug symtab/29106] new DWARF reader should de-duplicate functions

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29106

--- Comment #4 from Tom Tromey <tromey at sourceware dot org> ---
FWIW with -readnow I get 58 locations, but with ordinary "gdb"
(a /bin/gdb from before the new DWARF reader), I just get 4 locations.
So maybe the older index was a side effect of some kind
of erroneous duplication in partial symtabs.

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[Bug symtab/29106] new DWARF reader should de-duplicate functions

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29106

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |13.1

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[Bug symtab/29106] new DWARF reader should de-duplicate functions

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29106

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |INVALID

--- Comment #5 from Tom Tromey <tromey at sourceware dot org> ---
As part of another bug, I looked into this some more:

https://sourceware.org/pipermail/gdb-patches/2022-October/192662.html

In particular I generated a .gdb_index for a copy of gdb,
using both the old and new gdb (that is, before and after
the new DWARF reader).  Then I compared the list of symbols.

In every case I checked, the new gdb was correct.  (Well, to be
clear, there was one case that was incorrect, but I landed
a patch to fix this.)

So, I tend to think that the old index was simply missing some
entries, and nobody noticed.

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