[Bug 1901966] Re: Unable to stop at breakpoint in 32-bit executable

[Luis]

This doesn't seem to be related to the previous bugs.

I tried to reproduce this on 18.04.4 (I don't have 20.04) and a fresh
build of GDB master, and I couldn't.

(gdb) disass _start
Dump of assembler code for function _start:
   0x00010074 <+0>:     mov     r7, #4
   0x00010078 <+4>:     mov     r0, #1
   0x0001007c <+8>:     ldr     r1, [pc, #12]   ; 0x10090 <_start+28>
   0x00010080 <+12>:    ldr     r2, [pc, #12]   ; 0x10094 <_start+32>
   0x00010084 <+16>:    svc     0x00000000
   0x00010088 <+20>:    mov     r7, #1
   0x0001008c <+24>:    svc     0x00000000
   0x00010090 <+28>:    muleq   r2, r8, r0
   0x00010094 <+32>:    andeq   r0, r0, lr
End of assembler dump.
(gdb) b _start
Breakpoint 1 at 0x10074: file /tmp/hello.S, line 4.
(gdb) r
Starting program: /tmp/hello

Breakpoint 1, _start () at /tmp/hello.S:4
4               MOV R7, #4


With Ubuntu 18.04.4's GDB it also works.

Can you please turn on debugging and paste the log?

Use "set debug infrun 1" before the run command.

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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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