* Symbol can't be found unless type 'tab'
@ 2012-09-10 12:52 Yao Qi
2012-09-10 13:18 ` Jan Kratochvil
0 siblings, 1 reply; 8+ messages in thread
From: Yao Qi @ 2012-09-10 12:52 UTC (permalink / raw)
To: gdb
Hi,
I am trying to create a piece of fake dwarf information that a 8-byte
variable 'i' occupies two registers, as below, and it seems right to me.
Contents of the .debug_info section:
Compilation Unit @ offset 0x0:
Length: 0x34 (32-bit)
Version: 2
Abbrev Offset: 0
Pointer Size: 4
<0><b>: Abbrev Number: 1 (DW_TAG_compile_unit)
<c> DW_AT_name : set-reg.c
<16> DW_AT_producer : GNU C 3.3.3
<22> DW_AT_language : 2 (non-ANSI C)
<1><23>: Abbrev Number: 2 (DW_TAG_base_type)
<24> DW_AT_name : 8byte
<2a> DW_AT_byte_size : 8
<2b> DW_AT_encoding : 7 (unsigned)
<1><2c>: Abbrev Number: 3 (DW_TAG_variable)
<2d> DW_AT_name : i
<2f> DW_AT_type : <0x23>
<33> DW_AT_location : 0x0 (location list)
Contents of the .debug_loc section:
Offset Begin End Expression
00000000 080483d5 080483e6 (DW_OP_reg2 (edx); DW_OP_piece: 4;
DW_OP_reg3 (ebx); DW_OP_piece: 4)
00000000 <End of list>
However, the symbol 'i' can't be found unless I type 'tab' after command
'p'.
(gdb) p i
No symbol "i" in current context.
(gdb) p // type 'tab'
Display all 7422 possibilities? (y or n) // type 'n'
(gdb) p/x i
$2 = 0x45396ff4bfffeff4
Turning 'debug symtab-create' on tells me that 'tab' triggers creating
symtab, and I think that is the reason 'i' can be found after typing
'tab'. What should I complete/add in my faked dwarf information so that
symbol 'i' can be found directly when the executable is loaded? without
typing 'tab' to resolve symbol 'i'.
--
Yao
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Symbol can't be found unless type 'tab'
2012-09-10 12:52 Symbol can't be found unless type 'tab' Yao Qi
@ 2012-09-10 13:18 ` Jan Kratochvil
2012-09-12 7:45 ` Yao Qi
0 siblings, 1 reply; 8+ messages in thread
From: Jan Kratochvil @ 2012-09-10 13:18 UTC (permalink / raw)
To: Yao Qi; +Cc: gdb
On Mon, 10 Sep 2012 14:51:29 +0200, Yao Qi wrote:
> <1><2c>: Abbrev Number: 3 (DW_TAG_variable)
> <2d> DW_AT_name : i
> <2f> DW_AT_type : <0x23>
> <33> DW_AT_location : 0x0 (location list)
I guess because GDB does not like such complicated location expression for
glboal variables.
read_partial_die (const struct die_reader_specs *reader,
case DW_AT_location:
else if (attr_form_is_section_offset (&attr))
dwarf2_complex_location_expr_complaint ();
+
add_partial_symbol (struct partial_die_info *pdi, struct dwarf2_cu *cu)
case DW_TAG_variable:
if (pdi->d.locdesc)
addr = decode_locdesc (pdi->d.locdesc, cu);
There was a nice cleanup of it in:
[patch 2/2] Fix decode_locdesc for gcc-4.7.x optimized DWARF
http://sourceware.org/ml/gdb-patches/2011-07/msg00762.html
but I had to later revert it
[commit] [patch#2] fetch result of locdesc expressions as integer (not address)
http://sourceware.org/ml/gdb-patches/2011-10/msg00462.html
due to all the hacks on hacks in GDB needing to be cleaned up first.
Regards,
jan
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Symbol can't be found unless type 'tab'
2012-09-10 13:18 ` Jan Kratochvil
@ 2012-09-12 7:45 ` Yao Qi
2012-09-12 8:07 ` Jan Kratochvil
0 siblings, 1 reply; 8+ messages in thread
From: Yao Qi @ 2012-09-12 7:45 UTC (permalink / raw)
To: Jan Kratochvil; +Cc: gdb
On 09/10/2012 09:18 PM, Jan Kratochvil wrote:
> On Mon, 10 Sep 2012 14:51:29 +0200, Yao Qi wrote:
>> > <1><2c>: Abbrev Number: 3 (DW_TAG_variable)
>> > <2d> DW_AT_name : i
>> > <2f> DW_AT_type : <0x23>
>> > <33> DW_AT_location : 0x0 (location list)
> I guess because GDB does not like such complicated location expression for
> glboal variables.
Jan, thanks for the pointer.
The "symptom" is symbol is not found in psymtab, but in symtab when I
press 'tab' which triggers converting psymtab to symtab. I wonder why
symbol 'i' is *not* included in psymtab. Examine the source of
dwarf2read.c:add_partial_symbol, especially the case block for
'DW_TAG_variable', gives me some clue, and I add attribute
DW_AT_external to symbol 'i' like this,
<1><33>: Abbrev Number: 3 (DW_TAG_variable)
<34> DW_AT_name : i
<36> DW_AT_type : <0x2a>
<3a> DW_AT_external : 1 <--- here
<3b> DW_AT_location : 0x0 (location list)
and then symbol 'i' can be found by GDB without typing extra 'tab'.
--
Yao
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Symbol can't be found unless type 'tab'
2012-09-12 7:45 ` Yao Qi
@ 2012-09-12 8:07 ` Jan Kratochvil
2012-09-12 11:34 ` Yao Qi
0 siblings, 1 reply; 8+ messages in thread
From: Jan Kratochvil @ 2012-09-12 8:07 UTC (permalink / raw)
To: Yao Qi; +Cc: gdb
[-- Attachment #1: Type: text/plain, Size: 1928 bytes --]
On Wed, 12 Sep 2012 09:44:44 +0200, Yao Qi wrote:
> On 09/10/2012 09:18 PM, Jan Kratochvil wrote:
> >On Mon, 10 Sep 2012 14:51:29 +0200, Yao Qi wrote:
> >>> <1><2c>: Abbrev Number: 3 (DW_TAG_variable)
> >>> <2d> DW_AT_name : i
> >>> <2f> DW_AT_type : <0x23>
> >>> <33> DW_AT_location : 0x0 (location list)
> >I guess because GDB does not like such complicated location expression for
> >glboal variables.
>
> Jan, thanks for the pointer.
>
> The "symptom" is symbol is not found in psymtab, but in symtab when
> I press 'tab' which triggers converting psymtab to symtab. I wonder
> why symbol 'i' is *not* included in psymtab.
Because it has the complex location I suggested above.
> Examine the source of
> dwarf2read.c:add_partial_symbol, especially the case block for
> 'DW_TAG_variable', gives me some clue, and I add attribute
> DW_AT_external to symbol 'i' like this,
>
> <1><33>: Abbrev Number: 3 (DW_TAG_variable)
> <34> DW_AT_name : i
> <36> DW_AT_type : <0x2a>
> <3a> DW_AT_external : 1 <--- here
> <3b> DW_AT_location : 0x0 (location list)
>
> and then symbol 'i' can be found by GDB without typing extra 'tab'.
It is difficult to talk about the problem when you have not provided the
testcase, I have provided mine now.
But DW_AT_external is not significant to GDB as GDB can display even static
variables, even when they are not in current CU.
It is good to verify 'maintenance info symtabs' is empty during these
experiments, when one tries to print the variable.
I am very sure that this complex DW_AT_location is not properly supported by
psymtabs in GDB, this is one of the reasons I was doing the fix and its later
undo as I referenced in the previous mail.
Why didn't use just normal DWARF block, instead of the location list?
This part does not matter for your testcase and it will work with GDB.
Jan
[-- Attachment #2: i.c --]
[-- Type: text/plain, Size: 7 bytes --]
int i;
[-- Attachment #3: i.s --]
[-- Type: text/plain, Size: 2693 bytes --]
.file "i.c"
.text
.Ltext0:
.comm i,4,4
.Letext0:
.file 1 "i.c"
.section .debug_info,"",@progbits
.Ldebug_info0:
.long 1f - 2f # Length of Compilation Unit Info
2:
.value 0x4 # DWARF version number
.long .Ldebug_abbrev0 # Offset Into Abbrev. Section
.byte 0x8 # Pointer Size (in bytes)
.uleb128 0x1 # (DIE (0xb) DW_TAG_compile_unit)
.long .LASF0 # DW_AT_producer: "GNU C 4.6.3 20120306 (Red Hat 4.6.3-2) -mtune=generic -march=x86-64 -g"
.byte 0x2 # DW_AT_language
.ascii "i.c\0" # DW_AT_name
# .long .LASF1 # DW_AT_comp_dir: "/home/jkratoch/t"
# .long .Ldebug_line0 # DW_AT_stmt_list
.uleb128 0x2 # (DIE (0x1d) DW_TAG_variable)
.ascii "i\0" # DW_AT_name
# .byte 0x1 # DW_AT_decl_file (i.c)
# .byte 0x1 # DW_AT_decl_line
.long die30-.Ldebug_info0 # DW_AT_type
# DW_AT_external
.uleb128 0x9 # DW_AT_location
.byte 0x3 # DW_OP_addr
.quad i
die30:
.uleb128 0x3 # (DIE (0x30) DW_TAG_base_type)
.byte 0x8 # DW_AT_byte_size
.byte 0x5 # DW_AT_encoding
.ascii "int\0" # DW_AT_name
.byte 0 # end of children of DIE 0xb
1:
.section .debug_abbrev,"",@progbits
.Ldebug_abbrev0:
.uleb128 0x1 # (abbrev code)
.uleb128 0x11 # (TAG: DW_TAG_compile_unit)
.byte 0x1 # DW_children_yes
.uleb128 0x25 # (DW_AT_producer)
.uleb128 0xe # (DW_FORM_strp)
.uleb128 0x13 # (DW_AT_language)
.uleb128 0xb # (DW_FORM_data1)
.uleb128 0x3 # (DW_AT_name)
.uleb128 0x8 # (DW_FORM_string)
# .uleb128 0x1b # (DW_AT_comp_dir)
# .uleb128 0xe # (DW_FORM_strp)
# .uleb128 0x10 # (DW_AT_stmt_list)
# .uleb128 0x17 # (DW_FORM_sec_offset)
.byte 0
.byte 0
.uleb128 0x2 # (abbrev code)
.uleb128 0x34 # (TAG: DW_TAG_variable)
.byte 0 # DW_children_no
.uleb128 0x3 # (DW_AT_name)
.uleb128 0x8 # (DW_FORM_string)
# .uleb128 0x3a # (DW_AT_decl_file)
# .uleb128 0xb # (DW_FORM_data1)
# .uleb128 0x3b # (DW_AT_decl_line)
# .uleb128 0xb # (DW_FORM_data1)
.uleb128 0x49 # (DW_AT_type)
.uleb128 0x13 # (DW_FORM_ref4)
# .uleb128 0x3f # (DW_AT_external)
# .uleb128 0x19 # (DW_FORM_flag_present)
.uleb128 0x2 # (DW_AT_location)
.uleb128 0x18 # (DW_FORM_exprloc)
.byte 0
.byte 0
.uleb128 0x3 # (abbrev code)
.uleb128 0x24 # (TAG: DW_TAG_base_type)
.byte 0 # DW_children_no
.uleb128 0xb # (DW_AT_byte_size)
.uleb128 0xb # (DW_FORM_data1)
.uleb128 0x3e # (DW_AT_encoding)
.uleb128 0xb # (DW_FORM_data1)
.uleb128 0x3 # (DW_AT_name)
.uleb128 0x8 # (DW_FORM_string)
.byte 0
.byte 0
.byte 0
.section .debug_line,"",@progbits
.Ldebug_line0:
.section .debug_str,"MS",@progbits,1
.LASF0:
.string "GNU C 4.6.3 20120306 (Red Hat 4.6.3-2) -mtune=generic -march=x86-64 -g"
.LASF1:
.string "/home/jkratoch/t"
.ident "GCC: (GNU) 4.6.3 20120306 (Red Hat 4.6.3-2)"
.section .note.GNU-stack,"",@progbits
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Symbol can't be found unless type 'tab'
2012-09-12 8:07 ` Jan Kratochvil
@ 2012-09-12 11:34 ` Yao Qi
2012-09-12 12:33 ` Jan Kratochvil
0 siblings, 1 reply; 8+ messages in thread
From: Yao Qi @ 2012-09-12 11:34 UTC (permalink / raw)
To: Jan Kratochvil; +Cc: gdb
On 09/12/2012 04:06 PM, Jan Kratochvil wrote:
> Why didn't use just normal DWARF block, instead of the location list?
> This part does not matter for your testcase and it will work with GDB.
No special reason really. Are you suggesting create dwarf like this?
<1><33>: Abbrev Number: 3 (DW_TAG_variable)
<34> DW_AT_name : i
<36> DW_AT_type : <0x2a>
<3a> DW_AT_external : 1
<3b> DW_AT_location : 6 byte block: 52 93 4 53 93 4
(DW_OP_reg2 (edx); DW_OP_piece: 4; DW_OP_reg3 (ebx); DW_OP_piece: 4)
--
Yao
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Symbol can't be found unless type 'tab'
2012-09-12 11:34 ` Yao Qi
@ 2012-09-12 12:33 ` Jan Kratochvil
2012-09-12 13:37 ` Yao Qi
0 siblings, 1 reply; 8+ messages in thread
From: Jan Kratochvil @ 2012-09-12 12:33 UTC (permalink / raw)
To: Yao Qi; +Cc: gdb
On Wed, 12 Sep 2012 13:33:34 +0200, Yao Qi wrote:
> On 09/12/2012 04:06 PM, Jan Kratochvil wrote:
> >Why didn't use just normal DWARF block, instead of the location list?
> >This part does not matter for your testcase and it will work with GDB.
>
> No special reason really. Are you suggesting create dwarf like this?
>
> <1><33>: Abbrev Number: 3 (DW_TAG_variable)
> <34> DW_AT_name : i
> <36> DW_AT_type : <0x2a>
> <3a> DW_AT_external : 1
> <3b> DW_AT_location : 6 byte block: 52 93 4 53 93 4
> (DW_OP_reg2 (edx); DW_OP_piece: 4; DW_OP_reg3 (ebx); DW_OP_piece: 4)
Oops, you are right, this also cannot work.
You have to put it into a function as a local variable.
Sorry,
Jan
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Symbol can't be found unless type 'tab'
2012-09-12 12:33 ` Jan Kratochvil
@ 2012-09-12 13:37 ` Yao Qi
2012-09-12 13:45 ` Jan Kratochvil
0 siblings, 1 reply; 8+ messages in thread
From: Yao Qi @ 2012-09-12 13:37 UTC (permalink / raw)
To: Jan Kratochvil; +Cc: gdb
On 09/12/2012 08:32 PM, Jan Kratochvil wrote:
> On Wed, 12 Sep 2012 13:33:34 +0200, Yao Qi wrote:
>> On 09/12/2012 04:06 PM, Jan Kratochvil wrote:
>>> Why didn't use just normal DWARF block, instead of the location list?
>>> This part does not matter for your testcase and it will work with GDB.
>>
>> No special reason really. Are you suggesting create dwarf like this?
>>
>> <1><33>: Abbrev Number: 3 (DW_TAG_variable)
>> <34> DW_AT_name : i
>> <36> DW_AT_type : <0x2a>
>> <3a> DW_AT_external : 1
>> <3b> DW_AT_location : 6 byte block: 52 93 4 53 93 4
>> (DW_OP_reg2 (edx); DW_OP_piece: 4; DW_OP_reg3 (ebx); DW_OP_piece: 4)
>
> Oops, you are right, this also cannot work.
>
I am not sure what do you mean by "this also cannot work", but it works
for me, at least for my test purpose.
(gdb) b middle_middle
Breakpoint 1 at 0x80483ca
(gdb) run
Starting program:
/home/yao/Source/gnu/gdb/build-git/x86/gdb/testsuite/gdb.mi/mi-reg-changed
Breakpoint 1, 0x080483ca in middle_middle ()
(gdb) p/x i
$2 = 0x45396ff4bfffefe4
(gdb) p/x $ebx
$3 = 0x45396ff4
(gdb) p/x $edx
$4 = 0xbfffefe4
--
Yao
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: Symbol can't be found unless type 'tab'
2012-09-12 13:37 ` Yao Qi
@ 2012-09-12 13:45 ` Jan Kratochvil
0 siblings, 0 replies; 8+ messages in thread
From: Jan Kratochvil @ 2012-09-12 13:45 UTC (permalink / raw)
To: Yao Qi; +Cc: gdb
On Wed, 12 Sep 2012 15:36:44 +0200, Yao Qi wrote:
> I am not sure what do you mean by "this also cannot work", but it
> works for me, at least for my test purpose.
This is because 'b middle_middle' has expanded psymtab->symtab.
If you do 'p/x i' as the very first GDB command it will not work.
You could also keep there the location list in such case, it would work the
same.
See what you will see with 'set complaints 100', 'file ./gdb.mi/mi-reg-changed'.
I believe it would make the testcase magic if you move the 'i' variable DIE
into some function. But if you put some warning into the testcase source it
is IMO also acceptable the way you have it.
Thanks,
Jan
^ permalink raw reply [flat|nested] 8+ messages in thread
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2012-09-10 12:52 Symbol can't be found unless type 'tab' Yao Qi
2012-09-10 13:18 ` Jan Kratochvil
2012-09-12 7:45 ` Yao Qi
2012-09-12 8:07 ` Jan Kratochvil
2012-09-12 11:34 ` Yao Qi
2012-09-12 12:33 ` Jan Kratochvil
2012-09-12 13:37 ` Yao Qi
2012-09-12 13:45 ` Jan Kratochvil
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