* ptype output for multi-dimensional arrays using CTF
@ 2021-09-03 14:00 Indu Bhagat
2021-09-03 14:13 ` Indu Bhagat
0 siblings, 1 reply; 3+ messages in thread
From: Indu Bhagat @ 2021-09-03 14:00 UTC (permalink / raw)
To: Weimin Pan; +Cc: gdb-patches
Hello Weimin,
I ran into the following behavior with GDB. It seems like a GDB/CTF issue.
Using gcc/trunk and binutils-gdb/trunk'ish :)
Thanks
Indu
-------------------------
$ cat typedef-array.c
typedef int A[2][3];
A a = {{4, 5, 6}, {7, 8, 9}};
$ gcc -gctf -c typedef-array.c
$ gdb typedef-array.o
...
(gdb) ptype A
type = int [3][2]
(gdb) ptype a
type = int [3][2]
$ objdump --ctf=.ctf typedef-array.o
...
Variables:
a -> 0x5: (kind 10) A (size 0x18) (aligned at 0x4) -> 0x4: (kind 4)
int [2][3] (size 0x18) (aligned at 0x4) -> 0x3: (kind 4) int [2] (size
0x8) (aligned at 0x4) -> 0x1: (kind 1) int (format 0x1) (size 0x4)
(aligned at 0x4)
Types:
...
0x5: (kind 10) A (size 0x18) (aligned at 0x4) -> 0x4: (kind 4) int
[2][3] (size 0x18) (aligned at 0x4) -> 0x3: (kind 4) int [2] (size 0x8)
(aligned at 0x4) -> 0x1: (kind 1) int (format 0x1) (size 0x4) (aligned
at 0x4)
As you see, objdump reports the type correctly.
For reference, here's what DWARF gives:
$ gcc -g -c typedef-array.c
$ gdb typedef-array.o
(gdb) ptype A
type = int [2][3]
(gdb) ptype a
type = int [2][3]
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: ptype output for multi-dimensional arrays using CTF
2021-09-03 14:00 ptype output for multi-dimensional arrays using CTF Indu Bhagat
@ 2021-09-03 14:13 ` Indu Bhagat
2021-09-03 16:39 ` Weimin Pan
0 siblings, 1 reply; 3+ messages in thread
From: Indu Bhagat @ 2021-09-03 14:13 UTC (permalink / raw)
To: Weimin Pan; +Cc: gdb-patches, Nick Alcock
On 9/3/21 7:00 AM, Indu Bhagat wrote:
> Hello Weimin,
>
> I ran into the following behavior with GDB. It seems like a GDB/CTF issue.
>
> Using gcc/trunk and binutils-gdb/trunk'ish :)
>
> Thanks
> Indu
>
> -------------------------
>
> $ cat typedef-array.c
> typedef int A[2][3];
> A a = {{4, 5, 6}, {7, 8, 9}};
> $ gcc -gctf -c typedef-array.c
> $ gdb typedef-array.o
> ...
> (gdb) ptype A
> type = int [3][2]
> (gdb) ptype a
> type = int [3][2]
>
> $ objdump --ctf=.ctf typedef-array.o
> ...
> Variables:
> a -> 0x5: (kind 10) A (size 0x18) (aligned at 0x4) -> 0x4: (kind 4)
> int [2][3] (size 0x18) (aligned at 0x4) -> 0x3: (kind 4) int [2] (size
> 0x8) (aligned at 0x4) -> 0x1: (kind 1) int (format 0x1) (size 0x4)
> (aligned at 0x4)
>
> Types:
> ...
> 0x5: (kind 10) A (size 0x18) (aligned at 0x4) -> 0x4: (kind 4) int
> [2][3] (size 0x18) (aligned at 0x4) -> 0x3: (kind 4) int [2] (size 0x8)
> (aligned at 0x4) -> 0x1: (kind 1) int (format 0x1) (size 0x4) (aligned
> at 0x4)
>
> As you see, objdump reports the type correctly.
>
> For reference, here's what DWARF gives:
>
> $ gcc -g -c typedef-array.c
> $ gdb typedef-array.o
>
> (gdb) ptype A
> type = int [2][3]
> (gdb) ptype a
> type = int [2][3]
This could be related (or not). But here is another testcase where the
GDB results are not correct.
$ cat func-array-arg.c
int foo (int a, int b[a][a])
{
return b[a-1][a-3];
}
$ gcc -gctf -c func-array-arg.c
$ objdump --ctf=.ctf func-array-arg.o
...
Function objects:
foo -> 0x2: (kind 5) int (*) (int, int (*)[0]) (aligned at 0x8)
Types:
0x2: (kind 5) int (*) (int, int (*)[0]) (aligned at 0x8)
...
0x5: (kind 3) int (*)[0] (size 0x8) (aligned at 0x8) -> 0x4: (kind
4) int [0] (size 0x0) (aligned at 0x4) -> 0x1: (kind 1) int (format 0x1)
(size 0x4) (aligned at 0x4)
We are aware of this representation limit of CTF, but at present, using
0 is the best we can do. What I think is not correct is the behavior of
GDB around this.
$ gdb func-array-arg.o
...
(gdb) ptype foo
type = int (int, void)
For reference, here is the output with DWARF:
$ gcc -g -c func-array-arg.c
$ gdb func-array-arg.o
...
(gdb) ptype foo
type = int (int, int (*)[variable length])
Thanks
Indu
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: ptype output for multi-dimensional arrays using CTF
2021-09-03 14:13 ` Indu Bhagat
@ 2021-09-03 16:39 ` Weimin Pan
0 siblings, 0 replies; 3+ messages in thread
From: Weimin Pan @ 2021-09-03 16:39 UTC (permalink / raw)
To: Indu Bhagat; +Cc: gdb-patches, Nick Alcock
On 9/3/2021 7:13 AM, Indu Bhagat wrote:
> On 9/3/21 7:00 AM, Indu Bhagat wrote:
>> Hello Weimin,
>>
>> I ran into the following behavior with GDB. It seems like a GDB/CTF
>> issue.
>>
>> Using gcc/trunk and binutils-gdb/trunk'ish :)
>>
>> Thanks
>> Indu
>>
>> -------------------------
>>
>> $ cat typedef-array.c
>> typedef int A[2][3];
>> A a = {{4, 5, 6}, {7, 8, 9}};
>> $ gcc -gctf -c typedef-array.c
>> $ gdb typedef-array.o
>> ...
>> (gdb) ptype A
>> type = int [3][2]
>> (gdb) ptype a
>> type = int [3][2]
>>
>> $ objdump --ctf=.ctf typedef-array.o
>> ...
>> Variables:
>> a -> 0x5: (kind 10) A (size 0x18) (aligned at 0x4) -> 0x4: (kind
>> 4) int [2][3] (size 0x18) (aligned at 0x4) -> 0x3: (kind 4) int [2]
>> (size 0x8) (aligned at 0x4) -> 0x1: (kind 1) int (format 0x1) (size
>> 0x4) (aligned at 0x4)
>>
>> Types:
>> ...
>> 0x5: (kind 10) A (size 0x18) (aligned at 0x4) -> 0x4: (kind 4)
>> int [2][3] (size 0x18) (aligned at 0x4) -> 0x3: (kind 4) int [2]
>> (size 0x8) (aligned at 0x4) -> 0x1: (kind 1) int (format 0x1) (size
>> 0x4) (aligned at 0x4)
>>
>> As you see, objdump reports the type correctly.
>>
>> For reference, here's what DWARF gives:
>>
>> $ gcc -g -c typedef-array.c
>> $ gdb typedef-array.o
>>
>> (gdb) ptype A
>> type = int [2][3]
>> (gdb) ptype a
>> type = int [2][3]
>
> This could be related (or not). But here is another testcase where the
> GDB results are not correct.
>
> $ cat func-array-arg.c
> int foo (int a, int b[a][a])
> {
> return b[a-1][a-3];
> }
>
> $ gcc -gctf -c func-array-arg.c
> $ objdump --ctf=.ctf func-array-arg.o
> ...
> Function objects:
> foo -> 0x2: (kind 5) int (*) (int, int (*)[0]) (aligned at 0x8)
>
> Types:
>
> 0x2: (kind 5) int (*) (int, int (*)[0]) (aligned at 0x8)
> ...
> 0x5: (kind 3) int (*)[0] (size 0x8) (aligned at 0x8) -> 0x4: (kind
> 4) int [0] (size 0x0) (aligned at 0x4) -> 0x1: (kind 1) int (format
> 0x1) (size 0x4) (aligned at 0x4)
>
> We are aware of this representation limit of CTF, but at present,
> using 0 is the best we can do. What I think is not correct is the
> behavior of GDB around this.
>
> $ gdb func-array-arg.o
> ...
> (gdb) ptype foo
> type = int (int, void)
>
> For reference, here is the output with DWARF:
>
> $ gcc -g -c func-array-arg.c
> $ gdb func-array-arg.o
> ...
> (gdb) ptype foo
> type = int (int, int (*)[variable length])
>
> Thanks
> Indu
>
Hi Indu,
Thank you for the report. Reversing ranges of a multi-dimensional array
fixes
the first problem. The second problem was caused by a function argument
having a forward reference and is also fixed.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2021-09-03 14:00 ptype output for multi-dimensional arrays using CTF Indu Bhagat
2021-09-03 14:13 ` Indu Bhagat
2021-09-03 16:39 ` Weimin Pan
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