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digitalmars.D.bugs - [Issue 4149] New: refs displayed as pointers in gdb

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           Summary: refs displayed as pointers in gdb
           Product: D
           Version: unspecified
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: braddr puremagic.com
            Blocks: 4044


--- Comment #0 from Brad Roberts <braddr puremagic.com> 2010-05-02 13:36:57 PDT
---
(gdb) list inline.d:1
1  module test.d;
2
3  void foo(ref int x)
4  {
5      ++x;
6  }
7
8  void bar()
9  {
10     int x = 0;
11
12     foo(x);
13 }
14
15 void main()
16 {
17     bar();
18 }

(gdb) break 5
Breakpoint 1 at 0x804910d: file inline.d, line 5.
(gdb) run
Breakpoint 1, test.d.foo (x=0xbffff62c) at inline.d:5
5      ++x;
(gdb) print x
$1 = (int *) 0xbffff62c

Assuming I'm understanding the dwarf records correctly, foo's argument:
 <2><a2>: Abbrev Number: 5 (DW_TAG_formal_parameter)
    <a3>   DW_AT_name        : x
    <a5>   DW_AT_type        : <0x69>
    <a9>   DW_AT_location    : 2 byte block: 91 7c    (DW_OP_fbreg: -4)

And type 0x69:
 <1><69>: Abbrev Number: 4 (DW_TAG_pointer_type)
    <6a>   DW_AT_byte_size   : 4
    <6b>   DW_AT_type        : <0x62>


Dwarf formally supports a reference type according to the spec.

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Robert Clipsham <robert octarineparrot.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |robert octarineparrot.com


--- Comment #1 from Robert Clipsham <robert octarineparrot.com> 2010-05-02
21:44:31 BST ---
This is done because C does not have reference types, and no debugger currently
supports the debug output produced by dmd when using -g. When using -g dmd
should, as you say, use the DWARF reference type, which it does not currently
do. When using -gc, it should be a pointer as it is now. I'll try and put a
patch together later today. As a side note, classes should be reference types
too, rather than acting as pointers as they do currently.

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--- Comment #2 from Brad Roberts <braddr puremagic.com> 2010-05-02 13:48:41 PDT
---
Depends on if gc implies c, c++, or 'as much as is supported in the built-in
debug format without extension'. 

I'd argue for the last definition.  Given that dwarf supports it without
extension, I'd argue that it should use it.  I'd argue that -g should be
built-in + d extensions.

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--- Comment #3 from Robert Clipsham <robert octarineparrot.com> 2010-05-02
21:50:30 BST ---
-gc means act as C. I think I'm going to talk to Walter about this actually, as
the debugging situation for D could be far better.

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--- Comment #4 from Brad Roberts <braddr puremagic.com> 2010-05-02 14:15:36 PDT
---
I've been looking at how to patch up that part of the code, and it looks like
the ref-ness has been lost at this layer:

(gdb) print *t
$2 = {id = 4660, Tty = 29, Tflags = 0, Tmangle = 7 '\a', Tcount = 1, Tnext =
0x81ffd20, {Tdim = 0, Tel = 0x0, Tparamtypes = 0x0, Ttag = 0x0, Tident = 0x0,
Tkey = 0x0}, Texcspec = 0x0}
(gdb) print t->Tnext
$3 = (TYPE *) 0x81ffd20
(gdb) print t->Tnext[0]
$4 = {id = 4660, Tty = 10, Tflags = 0, Tmangle = 0 '\000', Tcount = 3, Tnext =
0x0, {Tdim = 0, Tel = 0x0, Tparamtypes = 0x0, Ttag = 0x0, Tident = 0x0, Tkey =
0x0}, Texcspec = 0x0}

Tty 29 == 0x1d == TYnptr

If it was still a TYnref, it'd be easy.

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--- Comment #5 from Robert Clipsham <robert octarineparrot.com> 2010-05-02
22:17:49 BST ---
It is easy, I wrote the patch that adds support for ref types to the debug info
;) The refness isn't lost, it just uses the same case statement, and thus gets
replaced. I'm about to write a patch for it now :)

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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla digitalmars.com


--- Comment #6 from Walter Bright <bugzilla digitalmars.com> 2010-05-02
16:14:03 PDT ---
I agree with Brad's comment 2.

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--- Comment #7 from Brad Roberts <braddr puremagic.com> 2010-05-09 01:09:56 PDT
---
Created an attachment (id=625)
Fix some plumbing and change the dwarf code to emit ref types.

The ref'ness was lost before it got into the dwarf stage, but also easy to fix,
assuming that Walter is right about the backend being ready to handle TYref's
now.

I've attached the diff I've whipped up.  It does work to emit the right debug
info, but I haven't tested it on much more than the simplest code
(specifically, the code at the top of this bug report).

A snippit from a gdb session:

Breakpoint 1, test.foo (x= 0xbffff62c) at inline.d:5
5      ++x;
(gdb) print x
$1 = (int &)  0xbffff62c: 0
(gdb) next
0x08049112 in test.foo (x= 0xbffff62c)
(gdb) print x
$2 = (int &)  0xbffff62c: 1

So, gdb is using C++ style demangling, but that can be addressed by someone
working on gdb.

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Brad Roberts <braddr puremagic.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
    Attachment #625|application/octet-stream    |text/plain
          mime type|                            |
 Attachment #625 is|0                           |1
              patch|                            |


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--- Comment #8 from Brad Roberts <braddr puremagic.com> 2010-05-09 04:29:06 PDT
---
Looks like one more minor change is needed to build phobos with these changes:

backed/cgcod.c:
   -1508,6 +1508,7    regm_t regmask(tym_t tym, tym_t tyf)
         case TYnptr:
         case TYsptr:
         case TYcptr:
+        case TYref:
             return mAX;
         case TYfloat:
         case TYifloat:

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Robert Clipsham <robert octarineparrot.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch


--- Comment #9 from Robert Clipsham <robert octarineparrot.com> 2010-05-09
15:29:05 BST ---
If this patch is accepted, we should probably change the DW_AT_language to be
C++ instead of C with -gc, and update the help message to say so.

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--- Comment #10 from Walter Bright <bugzilla digitalmars.com> 2012-01-18
20:52:37 PST ---
Can this be turned into a pull request?

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--- Comment #11 from Brad Roberts <braddr puremagic.com> 2012-01-18 20:55:55
PST ---
Last time I played with this diff on current code, it caused failures.  I
haven't looked at in any detail in ages and I'm fairly sure it's rather
incomplete now that I know more about the backend.

The bug is still real though.

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Leandro Lucarella <leandro.lucarella sociomantic.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |leandro.lucarella sociomant
                   |                            |ic.com


--- Comment #12 from Leandro Lucarella <leandro.lucarella sociomantic.com>
2012-01-26 07:04:10 PST ---
(In reply to comment #6)
 I agree with Brad's comment 2.
What's the relation between this and pull request 526[1] (commit e81dbc2 in dmd-1.x) that has been merged recently. At least according to the pull request, the improved usage of DWARF is only activated when -g is specified. Should that be changed for -gc? What about bug 3389? I think Robert's suggestion about having a -gd for D extensions and -g for standard debugging stuff would be better. Right now the situation with -g/-gc is far from ideal. [1] https://github.com/D-Programming-Language/dmd/pull/526 -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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dawg dawgfoto.de changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dawg dawgfoto.de
         AssignedTo|nobody puremagic.com        |dawg dawgfoto.de


--- Comment #13 from dawg dawgfoto.de 2012-01-31 13:52:52 PST ---
It's unrelated to pull 526 which fixed #4180.

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--- Comment #14 from Leandro Lucarella <leandro.lucarella sociomantic.com>
2012-02-01 02:22:04 PST ---
(In reply to comment #13)
 It's unrelated to pull 526 which fixed #4180.
I'm talking about the comment 2 by Brad:
 Depends on if gc implies c, c++, or 'as much as is supported in the built-in
 debug format without extension'. 
 
 I'd argue for the last definition.  Given that dwarf supports it without
 extension, I'd argue that it should use it.  I'd argue that -g should be
 built-in + d extensions.
Walter expressed he agree with this comment in comment 3. AFAIK this pull request works for -g instead of -gc, even when it uses standard DWARF features, which goes against that comment. In the bug 3389 that you just closed, Robert Clipsham makes what for me is a good point:
 -g not working is how it's meant to be, at least until gdb adds support for the
 D extensions to DWARF. I've hopefully fixed the remaining bugs with -gc (on
 linux at least). My solution to this would be to add in a -gd, and make -g an
 alias to -gc until better support for debug info is added to debuggers. This
 way users get working debug output with -g, and don't blame it on a buggy dmd
 :)
At least this will be more familiar with people used to GCC command line arguments (which is probably 100% of the *nix world), where -g is the default for debug and you have, for example -ggdb for GDB extensions. AFAIK there is no clear direction about this. But maybe is a topic for another bug report, I think I'll reopen bug 3389 because the root issue in that bug is what's being discussed here. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #15 from Brad Roberts <braddr puremagic.com> 2012-02-01 21:03:43
PST ---
Please stop cluttering this bug report with discussion about the meaning of -g,
that's a solved problem.  This report is about preserving 'ref'ness through the
backend and dwarf debug data.

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--- Comment #16 from dawg dawgfoto.de 2012-02-02 15:44:42 PST ---
https://github.com/D-Programming-Language/dmd/pull/687

Based on patch but had to add another change to e2ir.c.

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