[Bug 1901966] Re: Unable to stop at breakpoint in 32-bit executable
James Foster
1901966 at bugs.launchpad.net
Tue Nov 17 18:18:01 UTC 2020
I've been able to reproduce the problem on 32-bit Ubuntu 20.04 for RPi4.
The problem reproduces when the following is linked:
ld-linux-armhf.so.3 -> ld-2.31.so*
fostja at cptr280-arm:~/code/asm$ gdb -q hello
GEF for linux ready, type `gef' to start, `gef config' to configure
75 commands loaded for GDB 9.2 using Python engine 3.8
[*] 5 commands could not be loaded, run `gef missing` to know why.
Reading symbols from hello...
gef➤ set debug infrun 1
gef➤ b _start
Breakpoint 1 at 0x1016c: file hello.s, line 5.
gef➤ start
infrun: infrun_async(1)
infrun: proceed (addr=0xb6fd5a80, signal=GDB_SIGNAL_0)
infrun: proceed: resuming process 10100
infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current thread [process 10100] at 0xb6fd5a80
infrun: prepare_to_wait
infrun: target_wait (-1.0.0, status) =
infrun: -1.0.0 [process -1],
infrun: status->kind = ignore
infrun: handle_inferior_event status->kind = ignore
infrun: prepare_to_wait
infrun: target_wait (-1.0.0, status) =
infrun: -1.0.0 [process -1],
infrun: status->kind = ignore
infrun: handle_inferior_event status->kind = ignore
infrun: prepare_to_wait
When I revert to the following then things work properly:
ld-linux-armhf.so.3 -> ld-2.28.so*
So I have a work-around. It appears that the problem was introduced
between 2.28 and 2.31.
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https://bugs.launchpad.net/bugs/1901966
Title:
Unable to stop at breakpoint in 32-bit executable
Status in gdb package in Ubuntu:
New
Bug description:
I believe I'm having the problem described in #1846557 and #1848200.
Those bugs were reported fixed in 8.1.1 but I'm observing them in 9.2
so I suspect a regression (in fact, if I read the notes correctly, the
earlier reports were from another regression!).
I create a new EC2 server on AWS with Ubuntu Server 20.04 LTS (64-bit
Arm) then perform the following installs (not sure what is needed or
if something is missing):
```
sudo dpkg --add-architecture armhf
sudo apt update
sudo apt upgrade -y
sudo apt install -y build-essential vim binutils-arm-linux-gnueabi \
gdb libc6:armhf libstdc++6:armhf
```
Then I create hello.s:
```
.text
.global _start
_start:
MOV R7, #4
MOV R0, #1
LDR R1, =hello
LDR R2, =hello_size
SWI 0
MOV R7, #1
SWI 0
.data
hello: .asciz "Hello world!\n"
.equ hello_size, (.-hello)
```
Then I assemble, link, and run, all with success. Finally, I try to
debug:
```
$ arm-linux-gnueabi-as -ggdb -mcpu=cortex-a57 -o out.o hello.s
$ arm-linux-gnueabi-ld out.o -dynamic-linker=/usr/lib/ld-linux-armhf.so.3 -o out
$ rm out.o
$ ./out
Hello world!
$ gdb out
GNU gdb (Ubuntu 9.2-0ubuntu1~20.04) 9.2
...
Reading symbols from out...
(gdb) b _start
Breakpoint 1 at 0x10074: file hello.s, line 4.
(gdb) run
Starting program: /home/ubuntu/280/out
```
At this point everything hangs until I press ^C:
```
^C
Program received signal SIGINT, Interrupt.
0x0000aaaaba072284 in ?? ()
(gdb) bt
#0 0x0000aaaaba072284 in ?? ()
#1 0x0000000000007232 in ?? ()
Backtrace stopped: previous frame identical to this frame (corrupt stack?)
(gdb) l
1 .text
2 .global _start
3 _start:
4 MOV R7, #4
5 MOV R0, #1
6 LDR R1, =hello
7 LDR R2, =hello_size
8 SWI 0
9 MOV R7, #1
10 SWI 0
(gdb) q
A debugging session is active.
Inferior 1 [process 29234] will be killed.
Quit anyway? (y or n) y
$
```
It appears that gdb generally works and recognizes the executable, but
breakpoints don't work. I'm new at Arm and don't have a lot of
experience with assembly (at least not since the early 1970s), so it
could easily be my problem but it seems suspiciously like an earlier
problem and I think what I've done should work.
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