[Bug c++/29896] New: GDB git doesn't recognize template function name

[Bug c++/29896] New: GDB git doesn't recognize template function name

[vimacs.hacks at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29896

            Bug ID: 29896
           Summary: GDB git doesn't recognize template function name
           Product: gdb
           Version: HEAD
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
          Assignee: unassigned at sourceware dot org
          Reporter: vimacs.hacks at gmail dot com
  Target Milestone: ---

First posted on https://sourceware.org/pipermail/gdb/2022-November/050431.html

GDB 12.1 works as expected in this case.

For the following C++ program built with "g++ -g -o test test.cc" (no matter
what optimization level used):


template <typename T = int>
int t0(int n)
{
     int sum = 0;
     for (int i = 0; i < n; ++i) {
         sum += i * i;
     }
     return sum;
}

int t1(int n)
{
     int sum = 0;
     for (int i = 0; i < n; ++i) {
         sum += i * i;
     }
     return sum;
}

int main()
{
     int a = t0(5);
     int b = t1(5);
     return a + b;
}

We cannot use "b t0" command, however, after I use tab completion once, GDB
recognize this:

(gdb) b t0
Function "t0" not defined.
Make breakpoint pending on future shared library load? (y or [n]) n
(gdb) #b t0<int>(int) 
(gdb) b t0
Breakpoint 1 at 0x117d: file test.cc, line 4.

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[Bug c++/29896] GDB git doesn't recognize template function name

[simark at simark dot ca]

https://sourceware.org/bugzilla/show_bug.cgi?id=29896

Simon Marchi <simark at simark dot ca> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
                 CC|                            |simark at simark dot ca
   Last reconfirmed|                            |2022-12-13
   Target Milestone|---                         |13.1
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Simon Marchi <simark at simark dot ca> ---
Confirmed.  It's a bit hard to bisect because we hit a bunch of other crashes
and compilation failure, but it's most likely due to the new DWARF reader. 
Adding the 13.1 milestone, hopefully we can fix it, since it's a regression.

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[Bug c++/29896] GDB git doesn't recognize template function name

[vimacs.hacks at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29896

--- Comment #2 from vimacs.hacks at gmail dot com <vimacs.hacks at gmail dot com> ---
Yes, it's hard to bisect. I once tried when I posted that mail.
I'm a little surprised GDB can recognize the function after a tab completion,
it looks like GDB can cache the completed names.

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[Bug c++/29896] GDB git doesn't recognize template function name

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29896

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tromey at sourceware dot org

--- Comment #3 from Tom Tromey <tromey at sourceware dot org> ---
What happens is that the first scan (the cooked index) takes
the name from the DWARF and gets "t0<>".  The cooked index
just uses strncasecmp to find entries, so it doesn't find
this name.

Full symbol name matching, I think, is done with strncmp_iw_with_mode,
which handles a lot of weird cases and ignores the "<>":

      /* Skip template parameters in STRING1 if STRING2 does not contain
         any.  E.g.:
[...]

So, that sucks.

I'm not completely sure how to solve it.  Perhaps stripping
the template parmaeters before recording the entry in the index would
work.

One idea is to have two entries, both with and without the parameters,
but I wonder about combinatorial explosion if there are nested templates
like a<>::b<>::c<>::d<> -- since the entries record parent information.

Another idea is to change the hashing and the lookup to use
strncmp_iw_with_mode somehow, at least for C++ names.

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[Bug c++/29896] GDB git doesn't recognize template function name

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29896

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 c++/29896] GDB git doesn't recognize template function name

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29896

--- Comment #4 from Tom Tromey <tromey at sourceware dot org> ---
> Another idea is to change the hashing

I forgot the index uses a sorted vector, not a hash table.

I tried using strcmp_iw_ordered, but that doesn't really
have the right semantics.  Now I'm working on a patch to
implement a custom comparison function.

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[Bug c++/29896] GDB git doesn't recognize template function name

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29896

Tom Tromey <tromey at sourceware dot org> changed:

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

--- Comment #5 from Tom Tromey <tromey at sourceware dot org> ---
Patch seems to work.

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[Bug c++/29896] GDB git doesn't recognize template function name

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29896

--- Comment #6 from Tom Tromey <tromey at sourceware dot org> ---
https://sourceware.org/pipermail/gdb-patches/2022-December/194795.html

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[Bug c++/29896] GDB git doesn't recognize template function name

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29896

--- Comment #7 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tom Tromey <tromey@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=ac37b79cc440e37fc704d425a6e450afb3c7ee89

commit ac37b79cc440e37fc704d425a6e450afb3c7ee89
Author: Tom Tromey <tromey@adacore.com>
Date:   Wed Dec 14 14:37:41 2022 -0700

    Fix parameter-less template regression in new DWARF reader

    PR c++/29896 points out a regression in the new DWARF reader.  It does
    not properly handle a case like "break fn", where "fn" is a template
    function.

    This happens because the new index uses strncasecmp to compare.
    However, to make this work correctly, we need a custom function that
    ignores template parameters.

    This patch adds a custom comparison function and fixes the bug.  A new
    test case is included.

    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29896

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[Bug c++/29896] GDB git doesn't recognize template function name

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29896

--- Comment #8 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The gdb-13-branch branch has been updated by Tom Tromey
<tromey@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=83d3152401cce0c6fd5cd2d4a140bbf5d89a5d9c

commit 83d3152401cce0c6fd5cd2d4a140bbf5d89a5d9c
Author: Tom Tromey <tromey@adacore.com>
Date:   Wed Dec 14 14:37:41 2022 -0700

    Fix parameter-less template regression in new DWARF reader

    PR c++/29896 points out a regression in the new DWARF reader.  It does
    not properly handle a case like "break fn", where "fn" is a template
    function.

    This happens because the new index uses strncasecmp to compare.
    However, to make this work correctly, we need a custom function that
    ignores template parameters.

    This patch adds a custom comparison function and fixes the bug.  A new
    test case is included.

    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29896

    (cherry picked from commit ac37b79cc440e37fc704d425a6e450afb3c7ee89)

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[Bug c++/29896] GDB git doesn't recognize template function name

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29896

Tom Tromey <tromey at sourceware dot org> changed:

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

--- Comment #9 from Tom Tromey <tromey at sourceware dot org> ---
Fixed.

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[Bug c++/29896] GDB git doesn't recognize template function name

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29896

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |---

--- Comment #10 from Tom Tromey <tromey at sourceware dot org> ---
Fix has a bug:
https://sourceware.org/pipermail/gdb-patches/2023-January/195828.html

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[Bug c++/29896] GDB git doesn't recognize template function name

[brobecker at gnat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29896

Joel Brobecker <brobecker at gnat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
                 CC|                            |brobecker at gnat dot com
         Resolution|---                         |FIXED

--- Comment #11 from Joel Brobecker <brobecker at gnat dot com> ---
For the record, Tom fixed this via this commit:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=c121e82c39659d1140b1a6a3cfd72c765741b9f5

This was also ported to the gdb-13-branch:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=7ba1fc5a18e0e5f61ab0939aed4f8b816a7a477a

Closing. Thanks Tom!

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