[Bug debug/39563] New: C block scopes have no DW_TAG_lexical_block

[Bug debug/39563] New: C block scopes have no DW_TAG_lexical_block

[jan dot kratochvil at redhat dot com]

GNU C 4.4.0 20090326 (experimental)
GDB variables lookup does not match the C code lookup.
Similiar C++ code in PR debug/39524 uses DW_TAG_lexical_block.

$ gdb -q ./externvar
(gdb) l 1
1       #include <stdlib.h>
2       
3       int var = 2;
4       
5       int
6       main (void)
7       {
8         int var = 1;
9       
10        if (var != 1)
11          abort ();
12      
13        {
14          extern int var;
15      
16          if (var != 2)
17            abort ();
18        }
19      
20        return 0;
21      }
(gdb) b 16
Breakpoint 1 at 0x4004d2: file externvar.c, line 16.
(gdb) r
Starting program: /tmp/externvar 
Breakpoint 1, main () at externvar.c:16
16          if (var != 2)
(gdb) p var
$1 = 1
(gdb) c
Continuing.
Program exited normally.
(gdb) q
------------------------------------------------------------------------------
    < c>   DW_AT_producer    : (indirect string, offset: 0xe): GNU C 4.4.0
20090326 (experimental)      
 <1><7d>: Abbrev Number: 5 (DW_TAG_subprogram)
    <7f>   DW_AT_name        : (indirect string, offset: 0x63): main    
    <8a>   DW_AT_low_pc      : 0x4004b8 
    <92>   DW_AT_high_pc     : 0x4004e9 
 <2><a2>: Abbrev Number: 6 (DW_TAG_variable)
    <a3>   DW_AT_name        : var      
    <a9>   DW_AT_type        : <0x34>   
    <ad>   DW_AT_location    : 2 byte block: 91 6c      (DW_OP_fbreg: -20)
 <1><b1>: Abbrev Number: 7 (DW_TAG_variable)
    <b2>   DW_AT_name        : var      
    <b8>   DW_AT_type        : <0x34>   
    <bc>   DW_AT_external    : 1        
    <bd>   DW_AT_location    : 9 byte block: 3 70 8 60 0 0 0 0 0       
(DW_OP_addr: 600870)

Missing there something like:
 <2><c0>: Abbrev Number: 6 (DW_TAG_lexical_block)
    <c1>   DW_AT_low_pc      : 0x4005b2 
    <c9>   DW_AT_high_pc     : 0x4005c2 
 <3><b1>: Abbrev Number: 7 (DW_TAG_variable)
    <b2>   DW_AT_name        : var      
    <b8>   DW_AT_type        : <0x34>   
    <bc>   DW_AT_external    : 1        
    <bd>   DW_AT_location    : 9 byte block: 3 70 8 60 0 0 0 0 0       
(DW_OP_addr: 600870)


-- 
           Summary: C block scopes have no DW_TAG_lexical_block
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: debug
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jan dot kratochvil at redhat dot com
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39563

[Bug debug/39563] C block scopes have no DW_TAG_lexical_block

[jan dot kratochvil at redhat dot com]

------- Comment #1 from jan dot kratochvil at redhat dot com  2009-03-26 22:57 -------
As DW_AT_external-DW_TAG_variable in the inner block is incompatible with
current GDB
http://sourceware.org/ml/gdb-patches/2009-03/msg00595.html

the current C++ method of DW_TAG_imported_declaration referencing the
file-level DW_AT_external-DW_TAG_variable may be more appropriate.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39563

[Bug debug/39563] C block scopes have no DW_TAG_lexical_block

[jakub at gcc dot gnu dot org]

------- Comment #2 from jakub at gcc dot gnu dot org  2009-03-27 12:38 -------
This seems to be just a C FE problem, C++ FE compiling the exact same testcase
gives the expected output (DW_TAG_lexical_block with DW_TAG_variable with
DW_AT_external).  So IMHO just the C FE should be fixed to handle it like the
C++ FE and if there are gdb bugs, they should be fixed in gdb.


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2009-03-27 12:38:16
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39563

[Bug debug/39563] C block scopes have no DW_TAG_lexical_block

[jakub at gcc dot gnu dot org]

------- Comment #3 from jakub at gcc dot gnu dot org  2009-03-27 16:33 -------
Created an attachment (id=17544)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17544&action=view)
gcc44-pr39563.patch

Untested fix.

The problem with this patch is that DW_AT_decl_file and DW_AT_decl_line of the
DW_AT_external DW_TAG_variable and DW_TAG_subprogram DIEs is wrong.  Say for:
extern void abort (void);

int var = 1;

int
main (void)
{
  int var = 2;
  if (var != 2)
    abort ();

  {
    extern int var;
    extern void abort (void);
    if (var != 1)
      abort ();
    {
      int var = 3;
      if (var != 3)
abort ();
      {
extern int var;
extern void abort (void);
if (var != 1)
  abort ();
      }
    }
  }

  return 0;
}

for all DW_AT_external DW_TAG_variable DIEs DW_AT_decl_line is 3 and for abort
DW_AT_decl_line is the last extern void abort (void) line.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39563

[Bug debug/39563] C block scopes have no DW_TAG_lexical_block

[jakub at gcc dot gnu dot org]

------- Comment #4 from jakub at gcc dot gnu dot org  2009-03-27 18:19 -------
Created an attachment (id=17547)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17547&action=view)
gcc44-pr39563.patch

Updated patch that preserves the correct location info for the nested extern
decls.


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jakub at gcc dot gnu dot org
                   |dot org                     |
             Status|NEW                         |ASSIGNED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39563

[Bug debug/39563] C block scopes have no DW_TAG_lexical_block

[jakub at gcc dot gnu dot org]

------- Comment #5 from jakub at gcc dot gnu dot org  2009-03-27 20:46 -------
Created an attachment (id=17548)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17548&action=view)
gcc44-pr39563.patch

Patch that actually bootstrapped/regtested successfully.
Jan, could you please test it with gdb/archer?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39563

[Bug debug/39563] C block scopes have no DW_TAG_lexical_block

[jan dot kratochvil at redhat dot com]

------- Comment #6 from jan dot kratochvil at redhat dot com  2009-03-28 21:34 -------
No regressions for GDB.
GDB requires the extra patch otherwise it still does not work with patched GCC:
http://sourceware.org/ml/gdb-patches/2009-03/msg00595.html

FYI the patch generates one extra file-scope declaration:
int f (void) { extern int var; return var; }

    < c>   DW_AT_producer    : (indirect string, offset: 0x0): GNU C 4.5.0
20090328 (experimental)      
 <1><2d>: Abbrev Number: 2 (DW_TAG_subprogram)
    <2f>   DW_AT_name        : f        
[...]
 <2><50>: Abbrev Number: 3 (DW_TAG_variable)
    <51>   DW_AT_name        : var      
    <55>   DW_AT_decl_file   : 1        
    <56>   DW_AT_decl_line   : 1        
    <57>   DW_AT_type        : <0x5e>   
    <5b>   DW_AT_external    : 1        
    <5c>   DW_AT_declaration : 1        
[...]
 <1><65>: Abbrev Number: 3 (DW_TAG_variable)
    <66>   DW_AT_name        : var      
    <6a>   DW_AT_decl_file   : 1        
    <6b>   DW_AT_decl_line   : 1        
    <6c>   DW_AT_type        : <0x5e>   
    <70>   DW_AT_external    : 1        
    <71>   DW_AT_declaration : 1        


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39563

[Bug debug/39563] C block scopes have no DW_TAG_lexical_block

[jakub at gcc dot gnu dot org]

------- Comment #7 from jakub at gcc dot gnu dot org  2009-03-30 14:35 -------
Subject: Bug 39563

Author: jakub
Date: Mon Mar 30 14:35:03 2009
New Revision: 145293

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=145293
Log:
        PR debug/39563
        * c-decl.c (struct c_binding): Add locus field.
        (bind): Add locus argument, set locus field from it.
        (pop_scope): For b->nested VAR_DECL or FUNCTION_DECL,
        add a DECL_EXTERNAL copy of b->decl to current BLOCK_VARS.
        (push_file_scope, pushtag, pushdecl, pushdecl_top_level,
        implicitly_declare, undeclared_variable, lookup_label,
        declare_label, c_make_fname_decl, c_builtin_function,
        c_builtin_function_ext_scope, store_parm_decls_newstyle): Adjust
        bind callers.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/c-decl.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39563

[Bug debug/39563] C block scopes have no DW_TAG_lexical_block

[jakub at gcc dot gnu dot org]

------- Comment #8 from jakub at gcc dot gnu dot org  2009-03-30 15:23 -------
Fixed on the trunk.


-- 

jakub at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39563

[Bug debug/39563] C block scopes have no DW_TAG_lexical_block

[jan dot kratochvil at redhat dot com]

------- Comment #9 from jan dot kratochvil at redhat dot com  2009-04-02 21:09 -------
Fixed in FSF GDB HEAD:
http://sourceware.org/ml/gdb-patches/2009-03/threads.html#00595
http://sourceware.org/ml/gdb-patches/2009-04/threads.html#00040
http://sourceware.org/ml/gdb-cvs/2009-04/msg00021.html
        gdb/
        * dwarf2read.c
        (new_symbol <DW_TAG_variable> <!DW_AT_location> <DW_AT_external>):
        Create the symbol in local scope.
        * symtab.h (cu->list_in_scope <LOC_UNRESOLVED>): New comment part.

        gdb/testsuite/
        * gdb.dwarf2/dw2-unresolved-main.c, gdb.dwarf2/dw2-unresolved.S,
        gdb.dwarf2/dw2-unresolved.exp: New.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39563