From: Wolfgang Wallner <wolfgang-wallner@gmx.at>
To: Shahab Vahedi <shahab.vahedi@gmail.com>
Cc: gdb@sourceware.org
Subject: Re: Removing old symbols when debugging code that relocates itself
Date: Thu, 26 May 2022 21:28:58 +0200 [thread overview]
Message-ID: <60bee27b-7aff-1ecd-25eb-fe19c8d684b8@gmx.at> (raw)
In-Reply-To: <Yo6p8oBdsUTmXanm@gmail.com>
Hi Shahab,
On 26.05.22 00:13, Shahab Vahedi wrote:
> Hi Wolfgang,
>
> On Wed, May 25, 2022 at 11:14:28PM +0200, Wolfgang Wallner via Gdb wrote:
>> It seems I can only remove the symbols that I have added with
>> add-symbol-file, but not the initial ones ...
>
> Maybe you could extract the symbol file [1] and then strip it away from
> the binary [2]. This way, you have to use "add-symbol-file" to add it
> in different stages and according to what you say you should be able
> to remove it after each adding.
>
> [1]
> $ objcopy --only-keep-debug uboot.bin uboot.sym
>
> [2]
> $ objcopy --strip-all uboot.bin uboot.strp
Thanks for the feedback!
I tried your recommendations, and while it seems to help somewhat,
unfortunately it does not fully solve my troubles.
Here is what I did:
1) Create the files as you described:
arm-linux-gnueabihf-objcopy --strip-all u-boot u-boot.strp
arm-linux-gnueabihf-objcopy --only-keep-debug u-boot my_u-boot.sym
Remark: The U-Boot build already creates a file called 'u-boot.sym', so
I gave my file another name (my_u-boot.sym).
The already existing u-boot.sym file is the symbol table as text file
created by calling 'objdump -t'.
2) I start QEMU as described in my first mail
3) I start GDB using the 'u-boot.strp' ELF file
4) As first command, I add 'my_u-boot.sym' via add-symbol-file
I then step through the code as described in my last mail, but
somehow in this configuration I cannot use GDB's 'until' command.
Using 'until' continues execution, and the temporary breakpoint is
never hit. It is interesting to note that this is *only in assembly*,
using 'until' works fine in C-files!
As a workaround for this issue I set explicit breakpoints.
5) I continue to step through the code, until I reach the relocated code. I
then drop all symbols via 'symbol-file', and add them back for the relocated
location via 'add-symbol-file'.
Showing information about breakpoints shows that there are no duplicate
breakpoints any more --> woohoo :)
(gdb) info breakpoints
Num Type Disp Enb Address What
1 breakpoint keep y 0x47f3c668 arch/arm/lib/crt0.S:156
breakpoint already hit 1 time
2 breakpoint keep y 0x47f3c754 arch/arm/lib/relocate.S:134
breakpoint already hit 1 time
While these breakpoints were set at the old locations, now they already
point
to the symbols at the relocated locations.
But when I try to set a new breakpoint, it is again a duplicate:
(gdb) break board_init_r
Breakpoint 3 at 0x1dc28 (2 locations)
(gdb) info breakpoints
Num Type Disp Enb Address What
1 breakpoint keep y 0x47f3c668 arch/arm/lib/crt0.S:156
breakpoint already hit 1 time
2 breakpoint keep y 0x47f3c754 arch/arm/lib/relocate.S:134
breakpoint already hit 1 time
3 breakpoint keep y <MULTIPLE>
3.1 y 0x0001dc28 <board_init_r+4>
3.2 y 0x47f58c24 in board_init_r at
common/board_r.c:817
So this leaves me with the following questions:
*) Does anyone know why the 'until' command stopped working with this
approach in assembly files? Is this expected, or is it a bug?
*) Why are there still duplicate breakpoints?
*) Are there other approaches to deal with relocated code?
While the objcopy steps have helped me, for a more permanent
workflow I would like to avoid them (e.g. it would be nice to
directly set up a debug environment in an IDE, and any required
extra steps between compilation and debugging would make that more
complicated)
regards, Wolfgang
Remark: I think there was a typo in my initial mail. The breakpoint in
relocate.S should be in line 134, not line 118.
prev parent reply other threads:[~2022-05-26 19:29 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-25 21:14 Wolfgang Wallner
2022-05-25 22:13 ` Shahab Vahedi
2022-05-26 19:28 ` Wolfgang Wallner [this message]
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