[Bug breakpoints/12528] New: Should we handle constructors that are garbage collected but their debug info isn't?

[Bug breakpoints/12528] New: Should we handle constructors that are garbage collected but their debug info isn't?

[dje at google dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12528

           Summary: Should we handle constructors that are garbage
                    collected but their debug info isn't?
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: breakpoints
        AssignedTo: unassigned@sourceware.org
        ReportedBy: dje@google.com


This is a general problem which normally isn't significant (YMMV).
But in the case of constructors it can happen in real world code.

GCC can emit two copies of a constructor, and then with -ffunction-sections
-Wl,--gc-sections one copy may get thrown away.  However the associated debug
info won't get thrown away, leading to gdb lossage.

$ cat c1c2.cc

class foo
{
 public:
  foo (int x);
  int _x;
};

class foo2 : public foo
{
 public:
  foo2 (int x);
};

foo::foo (int x)
  : _x (x)
{
}

foo2::foo2 (int x)
  : foo (x)
{ // line 21
}

int
main ()
{
  foo2 bar (3);
  return 0;
}
$ g++ -g -ffunction-sections -Wl,--gc-sections c1c2.cc
$ gdb a.out
[...]
(gdb) b 21
Breakpoint 1 at 0x20: file c1c2.cc, line 22. (2 locations)
(gdb) i b
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   <MULTIPLE>
1.1                         y     0x0000000000000020 c1c2.cc:22
1.2                         y     0x00000000004005c8 in foo2::foo2(int)
                                               at c1c2.cc:22
(gdb) r
Starting program: /home/dje/src/play/a.out
Warning:
Cannot insert breakpoint 1.
Error accessing memory address 0x20: Input/output error.

(gdb)

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[Bug breakpoints/12528] Should we handle constructors that are garbage collected but their debug info isn't?

[dje at google dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12528

dje at google dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ppluzhnikov at google dot
                   |                            |com

--- Comment #1 from dje at google dot com 2011-03-11 08:11:32 UTC ---
*** Bug 12568 has been marked as a duplicate of this bug. ***

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[Bug breakpoints/12528] Should we handle constructors that are garbage collected but their debug info isn't?

[cvs-commit at gcc dot gnu.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=12528

--- Comment #2 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> 2011-03-16 18:15:27 UTC ---
CVSROOT:    /cvs/src
Module name:    src
Changes by:    ppluzhnikov@sourceware.org    2011-03-16 18:15:20

Modified files:
    gdb            : dwarf2read.c ChangeLog 
    gdb/testsuite  : ChangeLog 
Added files:
    gdb/testsuite/gdb.base: break-on-linker-gcd-function.cc 
                            break-on-linker-gcd-function.exp 

Log message:
    ChangeLog:

    2011-03-16  Paul Pluzhnikov  <ppluzhnikov@google.com>

    PR gdb/12528
    * dwarf2read.c (noop_record_line): New function.
    (dwarf_decode_lines): Ignore line tables for GCd functions.

    testsuite/ChangeLog:

    2011-03-16  Paul Pluzhnikov  <ppluzhnikov@google.com>

    PR gdb/12528
    * gdb.base/Makefile.in: Adjust EXECUTABLES.
    * gdb.base/break-on-linker-gcd-function.exp: New test.
    * gdb.base/break-on-linker-gcd-function.cc: New file.

Patches:
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/dwarf2read.c.diff?cvsroot=src&r1=1.509&r2=1.510
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/ChangeLog.diff?cvsroot=src&r1=1.12822&r2=1.12823
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/testsuite/ChangeLog.diff?cvsroot=src&r1=1.2635&r2=1.2636
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/testsuite/gdb.base/break-on-linker-gcd-function.cc.diff?cvsroot=src&r1=NONE&r2=1.1
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/testsuite/gdb.base/break-on-linker-gcd-function.exp.diff?cvsroot=src&r1=NONE&r2=1.1

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[Bug breakpoints/12528] Should we handle constructors that are garbage collected but their debug info isn't?

[cvs-commit at gcc dot gnu.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=12528

--- Comment #3 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> 2011-03-16 18:16:35 UTC ---
CVSROOT:    /cvs/src
Module name:    src
Changes by:    ppluzhnikov@sourceware.org    2011-03-16 18:16:26

Modified files:
    gdb/testsuite/gdb.base: Makefile.in 

Log message:
    ChangeLog:

    2011-03-16  Paul Pluzhnikov  <ppluzhnikov@google.com>

    PR gdb/12528
    * dwarf2read.c (noop_record_line): New function.
    (dwarf_decode_lines): Ignore line tables for GCd functions.

    testsuite/ChangeLog:

    2011-03-16  Paul Pluzhnikov  <ppluzhnikov@google.com>

    PR gdb/12528
    * gdb.base/Makefile.in: Adjust EXECUTABLES.
    * gdb.base/break-on-linker-gcd-function.exp: New test.
    * gdb.base/break-on-linker-gcd-function.cc: New file.

Patches:
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/testsuite/gdb.base/Makefile.in.diff?cvsroot=src&r1=1.9&r2=1.10

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[Bug breakpoints/12528] Should we handle constructors that are garbage collected but their debug info isn't?

[ppluzhnikov at google dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12528

Paul Pluzhnikov <ppluzhnikov at google dot com> changed:

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

--- Comment #4 from Paul Pluzhnikov <ppluzhnikov at google dot com> 2011-03-16 18:22:29 UTC ---
Verified original test case is fixed as well.

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[Bug breakpoints/12528] Should we handle constructors that are garbage collected but their debug info isn't?

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=12528

--- Comment #5 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
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The branch, master has been updated
       via  00ba3162ed1633f9b27f3fdd450e076d3a3f2e90 (commit)
       via  c3b7b696c231416ac90fd9cb7d5ce735b3683356 (commit)
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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=00ba3162ed1633f9b27f3fdd450e076d3a3f2e90

commit 00ba3162ed1633f9b27f3fdd450e076d3a3f2e90
Author: Yao Qi <yao@codesourcery.com>
Date:   Mon Aug 18 09:57:40 2014 +0800

    Run dw2-var-zero-addr.exp with --readnow

    This patch is to extend dw2-var-zero-add.exp to cover the case that
    partial symtabl is not used while full symtab is used, in order to
    cover the changes in patch 2/3.  This patch restarts GDB with
    --readnow and does the same test again.

    gdb/testsuite:

    2014-09-19  Yao Qi  <yao@codesourcery.com>

        * gdb.dwarf2/dw2-var-zero-addr.exp: Move test into new proc test.
        Invoke test.  Restart GDB with --readnow and invoke test again.

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=c3b7b696c231416ac90fd9cb7d5ce735b3683356

commit c3b7b696c231416ac90fd9cb7d5ce735b3683356
Author: Yao Qi <yao@codesourcery.com>
Date:   Mon Aug 4 14:57:22 2014 +0800

    Check function is GC'ed

    I see the following fail on arm-none-eabi target,

    (gdb) b 24^M
    Breakpoint 1 at 0x4: file
    ../../../../git/gdb/testsuite/gdb.base/break-on-linker-gcd-function.cc,
    line 24.^M
    (gdb) FAIL: gdb.base/break-on-linker-gcd-function.exp: b 24

    Currently, we are using flag has_section_at_zero to determine whether
    address zero in debug info means the corresponding code has been
    GC'ed, like this:

        case DW_LNE_set_address:
          address = read_address (abfd, line_ptr, cu, &bytes_read);

          if (address == 0 && !dwarf2_per_objfile->has_section_at_zero)
            {
              /* This line table is for a function which has been
             GCd by the linker.  Ignore it.  PR gdb/12528 */

    However, this is incorrect on some bare metal targets, as .text
    section is located at 0x0, so dwarf2_per_objfile->has_section_at_zero
    is true.  If a function is GC'ed by linker, the address is zero.  GDB
    thinks address zero is a function's address rather than this function
    is GC'ed.

    In this patch, we choose 'lowpc' got in read_file_scope to check
    whether 'lowpc' is greater than zero.  If it isn't, address zero really
    means the function is GC'ed.  In this patch, we pass 'lowpc' in
    read_file_scope through handle_DW_AT_stmt_list and dwarf_decode_lines,
    and to dwarf_decode_lines_1 finally.

    This patch fixes the fail above. This patch also covers the path that
    partial symbol isn't used, which is tested by starting gdb with
    --readnow option.

    It is regression tested on x86-linux with
    target_board=dwarf4-gdb-index, and arm-none-eabi.  OK to apply?

    gdb:

    2014-09-19  Yao Qi  <yao@codesourcery.com>

        * dwarf2read.c (dwarf_decode_lines): Update declaration.
        (handle_DW_AT_stmt_list): Add argument 'lowpc'.  Update
        comments.  Callers update.
        (dwarf_decode_lines): Likewise.
        (dwarf_decode_lines_1): Add argument 'lowpc'.  Update
        comments.  Skip the line table if  'lowpc' is greater than
        'address'.  Don't check
        dwarf2_per_objfile->has_section_at_zero.

    gdb/testsuite:

    2014-09-19  Yao Qi  <yao@codesourcery.com>

        * gdb.base/break-on-linker-gcd-function.exp: Move test into new
        proc set_breakpoint_on_gcd_function.  Invoke
        set_breakpoint_on_gcd_function.  Restart GDB with --readnow and
        invoke set_breakpoint_on_gcd_function again.

-----------------------------------------------------------------------

Summary of changes:
 gdb/ChangeLog                                      |   11 ++++++
 gdb/dwarf2read.c                                   |   33 +++++++++++++------
 gdb/testsuite/ChangeLog                            |   12 +++++++
 .../gdb.base/break-on-linker-gcd-function.exp      |   24 +++++++++++---
 gdb/testsuite/gdb.dwarf2/dw2-var-zero-addr.exp     |   19 +++++++++--
 5 files changed, 80 insertions(+), 19 deletions(-)

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