This was discussed as part of bugzilla PR/21828. I have filed PR 23190.
$ cat t.c
static int foo;
int bar;
int main(void)
{
foo += 3;
bar *= 5;
return 0;
}
$ xgcc -g -O2 -o t t.c
$ cat gdbcmds
b main
ptype foo
ptype bar
p foo
p bar
$ gdb --batch -x gdbcmds t
Reading symbols for shared libraries ... done
Breakpoint 1 at 0x2d14: file t.c, line 6.
type = <unknown type>
type = <unknown type>
$1 = <unknown type>
$2 = <unknown type>
[ This was discussed in PR 21828 ]
>On Jul 22, 2005, at 4:43 PM, mark at codesourcery dot com wrote:
>
>First, your example was not the one in the original bug report.
>
>Second, you're using STABS, not DWARF-2. I suspect the stabs debug
>generator, or the GDB stabs reader is not as good as DWARF.
>
>On GNU/Linux, GDB knows that "bar" has type "int". It still doesn't
>know the type of "foo"; apparently too much of the debug
information is
>optimized away. But, that's some other problem -- perhaps in GDB
>itself. The information is clearly there for it:
>
> .uleb128 0x2 # (DIE (0x2d) DW_TAG_variable)
> .ascii "foo\0" # DW_AT_name
> .byte 0x1 # DW_AT_decl_file
> .byte 0x1 # DW_AT_decl_line
> .long 0x38 # DW_AT_type
> .uleb128 0x3 # (DIE (0x38) DW_TAG_base_type)
> .ascii "int\0" # DW_AT_name
> .byte 0x4 # DW_AT_byte_size
> .byte 0x5 # DW_AT_encoding
It seems this is related to order of cgraph_optimize() and writing
globals. If globals are wrapped up before emitting code then debug
info. is not emitted for uninitialized globals, because DECL_RTL is
not set. C++ FE writes globals before doing cgraph_optimize(), but C
FE optimizes first. This is why this is C specific only. This patch
fixes this but it causes varpool-1.c test failure. With this patch,
GDB know about foo as well as bar when DWARF is used.
Index: c-decl.c
===============================================================
====
RCS file: /cvs/gcc/gcc/gcc/c-decl.c,v
retrieving revision 1.677
diff -Idpatel.pbxuser -c -3 -p -r1.677 c-decl.c
*** c-decl.c 19 Jul 2005 20:19:09 -0000 1.677
--- c-decl.c 28 Jul 2005 19:22:47 -0000
*************** tree c_cont_label;
*** 131,136 ****
--- 131,139 ----
static GTY(()) tree all_translation_units;
+ /* Outermost block. */
+ static GTY(()) tree ext_block;
+
/* A list of decls to be made automatically visible in each file
scope. */
static GTY(()) tree visible_builtins;
*************** c_write_global_declarations_1 (tree glob
*** 7570,7576 ****
void
c_write_global_declarations (void)
{
! tree ext_block, t;
/* We don't want to do this if generating a PCH. */
if (pch_file)
--- 7573,7579 ----
void
c_write_global_declarations (void)
{
! tree t;
/* We don't want to do this if generating a PCH. */
if (pch_file)
*************** c_write_global_declarations (void)
*** 7586,7591 ****
--- 7589,7598 ----
external_scope = 0;
gcc_assert (!current_scope);
+ /* We're done parsing; proceed to optimize and emit assembly.
+ FIXME: shouldn't be the front end's responsibility to call
this. */
+ cgraph_optimize ();
+
/* Process all file scopes in this compilation, and the
external_scope,
through wrapup_global_declarations and
check_global_declarations. */
for (t = all_translation_units; t; t = TREE_CHAIN (t))
*************** c_write_global_declarations (void)
*** 7608,7617 ****
functions have magic names which are detected by collect2. */
build_cdtor ('I', static_ctors); static_ctors = 0;
build_cdtor ('D', static_dtors); static_dtors = 0;
-
- /* We're done parsing; proceed to optimize and emit assembly.
- FIXME: shouldn't be the front end's responsibility to call
this. */
- cgraph_optimize ();
}
#include "gt-c-decl.h"
--- 7615,7620 ----
-
Devang
