[Bug gdb/31463] New: Artificial variables in locals output

[Bug gdb/31463] New: Artificial variables in locals output

[dmitry.neverov at jetbrains dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=31463

            Bug ID: 31463
           Summary: Artificial variables in locals output
           Product: gdb
           Version: 14.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: dmitry.neverov at jetbrains dot com
  Target Milestone: ---

To reproduce compile the program (g++ -g -o main main.cpp):

#include <iostream>
#include <vector>

int main() {
  std::vector<int> v = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
  for (auto i : v) {
    std::cout << i << std::endl;
  }
  return 0;
}

Run gdb: 

$ gdb -q -batch main -ex "b main.cpp:7" -ex "run" -ex "info locals"

The output contains artificial symbols __for_range, __for_begin, __for_end:

Breakpoint 1, main () at main.cpp:7
7           std::cout << i << std::endl;
i = 1
__for_range = std::vector of length 10, capacity 10 = {1, 2, 3, 4, 5, 6, 7, 8,
9, 10}
__for_begin = 1
__for_end = 60721
v = std::vector of length 10, capacity 10 = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

These symbols also returned when iterating over a block
in python, and is_artificial is not exposed in python API.

This was fixed for Ada, but not other languages in
https://sourceware.org/bugzilla/show_bug.cgi?id=28180.

I've noticed, that in python such symbols have the line=0.
Is it correct to use this as a sign that the symbol is artificial?

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[Bug gdb/31463] Artificial variables in locals output

[sam at gentoo dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31463

Sam James <sam at gentoo dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://sourceware.org/bugz
                   |                            |illa/show_bug.cgi?id=28180
                 CC|                            |sam at gentoo dot org

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[Bug gdb/31463] Artificial variables in locals output

[ssbssa at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31463

Hannes Domani <ssbssa at sourceware dot org> changed:

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

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[Bug gdb/31463] Artificial variables in locals output

[dmitry.neverov at jetbrains dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=31463

--- Comment #1 from Dmitry Neverov <dmitry.neverov at jetbrains dot com> ---
I guess I take it back: `this` in c++ methods is also artificial and has
line=0, 
but should be shown.

I don't know if range-loop variables are shown by design or not.

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[Bug gdb/31463] Artificial variables in locals output

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31463

Tom Tromey <tromey at sourceware dot org> changed:

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

--- Comment #2 from Tom Tromey <tromey at sourceware dot org> ---
(In reply to Dmitry Neverov from comment #1)

> I don't know if range-loop variables are shown by design or not.

Normally gdb just does what the compiler tells it.

Ada is a bit special because it emits some forms of debuginfo
via symbol names.  By default there isn't much of this any
more, but there are still a few cases that can't be avoided.

It would be fine by me to give Python a way to detect artificiality.
Omitting artificial variables via some option would also be fine.

I suppose my view is that, overall, seeing these isn't too confusing,
and might be helpful in some cases when debugging.  It lets you
inspect a compiler transform and see some objects that would otherwise
be inaccessible -- like if you want to debug some iterator implementation.

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