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January 10, 2009
[Issue 2575] New: gdb can not show code
http://d.puremagic.com/issues/show_bug.cgi?id=2575

          Summary: gdb can not show code
          Product: D
          Version: 2.022
         Platform: PC
              URL: http://pastebin.com/m21fab94f
       OS/Version: Linux
           Status: NEW
         Severity: normal
         Priority: P2
        Component: DMD
       AssignedTo: bugzilla@digitalmars.com
       ReportedBy: jason.james.house@gmail.com


The URL shows how this bug typically manifests itself.  GDB seems to look for
.s files for assembly code and can't seem to find them.  This behavior exhibits
itself with all D2 programs I've tried, including void main(){}


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January 24, 2009
[Issue 2575] gdb can not show code
http://d.puremagic.com/issues/show_bug.cgi?id=2575





------- Comment #1 from jason.james.house@gmail.com  2009-01-24 11:16 -------
After a lot of help from volodya on irc #gdb, it looks like the issue is that
the low_pc and high_pc attributes are missing.

GDB can try to compensate for this (as if it was some legacy producer of debug
info) by walking the children, but it only looks at "namespace" and
"subprogram".  D has "module" which stops it.


--
January 24, 2009
[Issue 2575] gdb can not show code
http://d.puremagic.com/issues/show_bug.cgi?id=2575





------- Comment #2 from mihail.zenkov@gmail.com  2009-01-24 16:09 -------
Break points don't work with demangled name. Not sure but imho problem in
incorrect DW_AT_name and/or not provided DW_AT_MIPS_linkage by DMD.

DMD put mangled name to DW_AT_name:
<2><91>: Abbrev Number: 6 (DW_TAG_subprogram)
    DW_AT_sibling     : <c8>
    DW_AT_name        : _D5crash3fooFZv
    DW_AT_decl_file   : 1
    DW_AT_decl_line   : 12
    DW_AT_low_pc      : 0
    DW_AT_high_pc     : 0x16
    DW_AT_frame_base  : 1 byte block: 55       (DW_OP_reg5)

GDC/GCC put mangled name to DW_AT_MIPS_linkage_name and demandled to
DW_AT_name:
<1><bd>: Abbrev Number: 6 (DW_TAG_subprogram)
    DW_AT_external    : 1
    DW_AT_name        : foo
    DW_AT_decl_file   : 1
    DW_AT_decl_line   : 12
    DW_AT_MIPS_linkage_name: _D5crash3fooFZv
    DW_AT_low_pc      : 0x3b
    DW_AT_high_pc     : 0x51
    DW_AT_frame_base  : 0x43   (location list)

After fix DW_TAG_module you can try use mangled name, for example main - _Dmain


--
February 08, 2009
[Issue 2575] gdb can not show code
http://d.puremagic.com/issues/show_bug.cgi?id=2575





------- Comment #3 from mihail.zenkov@gmail.com  2009-02-07 20:56 -------
GDB also work fine with LDC debug info.

<1><a7>: Abbrev Number: 3 (DW_TAG_subprogram)
    DW_AT_name        : crash.foo
    DW_AT_MIPS_linkage_name: _D5crash3fooFZv
    DW_AT_external    : 1
    DW_AT_prototyped  : 1
    DW_AT_decl_file   : 1
    DW_AT_decl_line   : 11
    DW_AT_low_pc      : 0x20
    DW_AT_high_pc     : 0x21
    DW_AT_frame_base  : 1 byte block: 54       (DW_OP_reg4)


--
February 15, 2009
[Issue 2575] gdb can not show code
http://d.puremagic.com/issues/show_bug.cgi?id=2575


jason.james.house@gmail.com changed:

          What    |Removed                     |Added
----------------------------------------------------------------------------
               URL|http://pastebin.com/m21fab94|
                  |f                           |
          Severity|normal                      |major
           Version|2.022                       |2.025




------- Comment #4 from jason.james.house@gmail.com  2009-02-15 10:00 -------
It looks like the URL showing the problem has expired.  Here's a sample
session.  I upped the severity because this is a really painful bug in dmd for
me.  I'm forced to place tons of writefln statements into the code instead of
being able to step through it in the debugger



jhouse@jhouse-laptop:~/housebot/0.8$ gdb ./housebot-0.8 
GNU gdb 6.8-debian
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i486-linux-gnu"...
(gdb) break main
Breakpoint 1 at 0x8059e87
(gdb) run
Starting program: /home/jhouse/housebot/0.8/housebot-0.8 
[Thread debugging using libthread_db enabled]
[New Thread 0xb7c3eb00 (LWP 23503)]
[Switching to Thread 0xb7c3eb00 (LWP 23503)]

Breakpoint 1, 0x08059e87 in main ()
Current language:  auto; currently asm
(gdb) list
1       /tmp/ccPssJzP.s: No such file or directory.
       in /tmp/ccPssJzP.s
(gdb) quit
The program is running.  Exit anyway? (y or n) y
jhouse@jhouse-laptop:~/housebot/0.8$ 


--
February 20, 2009
[Issue 2575] gdb can not show code
http://d.puremagic.com/issues/show_bug.cgi?id=2575





------- Comment #5 from bugzilla@digitalmars.com  2009-02-20 04:42 -------
But dmd does emit the low_pc and high_pc data. Compile:

int foo(int i) { return i * i; }

with:

dmd -c -g foo.d

Then run dumpobj on it:

dumpobj -p foo.o

which will pretty-print the dwarf debug into. The attributes are there.


--
February 20, 2009
[Issue 2575] gdb can not show code
http://d.puremagic.com/issues/show_bug.cgi?id=2575





------- Comment #6 from jason.james.house@gmail.com  2009-02-20 07:54 -------
D'oh, if only I reported more information when I remembered it.

Trying now, I'm doing "objdump -Wgs <executable>" and then searching for
module.

What I see right before it is DW_TAG_compile_unit.  I don't see DW_AT_high_pc
and DW_AT_low_pc in that section, but I don't know if it's supposed to be
there.  The impression I got from my chats on #gdb was that the debug data was
stored in somewhat of a hierarchical structure.  In order to figure out the
offsets for the source file, it wanted to find the high and low attributes but
did not.  There's a workaround inside gdb that will walk the children in order
to get around the behavior of old compilers, but it's fragile.  Having modern
stuff such as DW_TAG_module stops it from operating (since it doesn't match
what old compilers did).

That's all I can remember/reproduce with some experimentation with objdump. 
Can you reproduce the problem?  Maybe chat with someone on #gdb?  I had to wait
~12 hours to get a response.  Once I did, they were very helpful.  I'll guess
the compile_unit should have high_pc and low_pc, but I'm only guessing.  If you
can reproduce the issue, then it should be easy to see if what you did works or
not.  Sorry for the lack of detail :(


--
February 25, 2009
[Issue 2575] gdb can not show code
http://d.puremagic.com/issues/show_bug.cgi?id=2575





------- Comment #7 from bugzilla@digitalmars.com  2009-02-25 00:30 -------
Looks like DW_AT_MIPS_linkage_name is an undocumented vendor extension to
Dwarf.


--
February 26, 2009
[Issue 2575] gdb can not show code
http://d.puremagic.com/issues/show_bug.cgi?id=2575





------- Comment #8 from mihail.zenkov@gmail.com  2009-02-25 20:46 -------
It undocumented but widely used. IMHO better use them for mangled name than
DW_AT_name. Current way violates DWARF:

"Because the names of program objects described by DWARF are the names as they
appear in the source program, implementations of language translators that use
some form of mangled name (as do many implementations of C++) should use the
unmangled form of the name in the DWARF DW_AT_name attribute, including the
keyword operator (in names such as “operator +”), if present. Sequences of
multiple whitespace characters may be compressed."


--
August 05, 2009
[Issue 2575] gdb can not show code
http://d.puremagic.com/issues/show_bug.cgi?id=2575





--- Comment #9 from Walter Bright <bugzilla@digitalmars.com>  2009-08-05 01:21:42 PDT ---
I'll add the MIPS_linkage tag and change the name tag. We'll see how far that
gets us.

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