[Bug gdb/31507] New: [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[Bug gdb/31507] New: [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

            Bug ID: 31507
           Summary: [gdb, aarch64] FAIL:
                    gdb.arch/disp-step-insn-reloc.exp:
                    can_relocate_adr_forward: relocated instruction
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

On aarch64-linux (debian 12) I ran into:
...
(gdb) PASS: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: go to
breakpoint 6
continue^M
Continuing.^M
^M
Breakpoint 8, can_relocate_adr_forward () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:356^M
356       asm ("set_point6:\n"^M
(gdb) FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward:
relocated instruction
...

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[Bug gdb/31507] [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
Doesn't reproduce all the time, but often enough:
...
$ for n in $(seq 1 10); do ./test.sh 2>&1 | grep "# of " | sort -u; done
# of expected passes            49
# of expected passes            37
# of unexpected failures        12
# of expected passes            49
# of expected passes            37
# of unexpected failures        12
# of expected passes            49
# of expected passes            36
# of unexpected failures        13
# of expected passes            49
# of expected passes            49
# of expected passes            46
# of unexpected failures        3
# of expected passes            49
...

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[Bug gdb/31507] [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

--- Comment #2 from Tom de Vries <vries at gcc dot gnu.org> ---
Created attachment 15413
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15413&action=edit
gdb.log without fail

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[Bug gdb/31507] [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

--- Comment #3 from Tom de Vries <vries at gcc dot gnu.org> ---
Created attachment 15414
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15414&action=edit
gdb.log with fail

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[Bug gdb/31507] [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

--- Comment #4 from Tom de Vries <vries at gcc dot gnu.org> ---
First relevant difference in gdb.log:
...
@@ -221,132 +221,133 @@
 (gdb) continue
 Continuing.

-Breakpoint 8, can_relocate_adr_forward () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:356
-356      asm ("set_point6:\n"
+Breakpoint 17, pass () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:31
+31     }
 (gdb) PASS: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: go to
breakpoint 6
 continue
 Continuing.

-Breakpoint 17, pass () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:31
-31     }
-(gdb) PASS: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward:
relocated instruction
+Breakpoint 8, can_relocate_adr_forward () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:356
+356      asm ("set_point6:\n"
+(gdb) FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward:
relocated instruction
...

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[Bug gdb/31507] [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

--- Comment #5 from Tom de Vries <vries at gcc dot gnu.org> ---
More minimal version:
...
$ cat gdb.in
file
/home/linux/gdb/build/gdb/testsuite/outputs/gdb.arch/disp-step-insn-reloc/disp-step-insn-reloc
start
break *set_point0
break *set_point1
break *set_point2
break pass
break fail
set displaced-stepping on
continue
bt
continue
bt
continue
bt
continue
bt
continue
bt
continue
bt
$ gdb -q -batch -ex "set trace-commands on" -x gdb.in 2>&1 | tee LOG; grep
Breakpoint LOG
...

Usually, we have:
...
Breakpoint 2, 0x0000aaaaaaaa08bc in can_relocate_b () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:128
Breakpoint 5, pass () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:31
Breakpoint 3, 0x0000aaaaaaaa090c in can_relocate_bcond_true () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:164
Breakpoint 5, pass () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:31
Breakpoint 4, 0x0000aaaaaaaa0958 in can_relocate_cbz () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:203
Breakpoint 5, pass () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:31
...

But once in a while:
...
Breakpoint 2, 0x0000aaaaaaaa08bc in can_relocate_b () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:128
Breakpoint 5, pass () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:31
Breakpoint 3, 0x0000aaaaaaaa090c in can_relocate_bcond_true () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:164
Breakpoint 5, pass () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:31
Breakpoint 5, pass () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:31
Breakpoint 4, 0x0000aaaaaaaa0958 in can_relocate_cbz () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:203
...

Looking at the backtrace, we hit pass twice without making progress:
...
+continue

Breakpoint 5, pass () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:31
31      }
+bt
#0  pass () at /home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:31
#1  0x0000aaaaaaaa0928 in can_relocate_bcond_true () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:179
#2  0x0000aaaaaaaa0c9c in main () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:629
+continue

Breakpoint 5, pass () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:31
31      }
+bt
#0  pass () at /home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:31
#1  0x0000aaaaaaaa0928 in can_relocate_bcond_true () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:179
#2  0x0000aaaaaaaa0c9c in main () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:629
...

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[Bug gdb/31507] [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

--- Comment #6 from Tom de Vries <vries at gcc dot gnu.org> ---
OK, so this hits the "PC did not move. Discarding PC adjustment" case:
...
Breakpoint 5, pass () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:31
31      }
+x /i $pc
=> 0xaaaaaaaa0894 <pass>:       nop
+continue
[displaced] displaced_step_prepare_throw: displaced-stepping 1307111.1307111.0
now
[displaced] displaced_step_prepare_throw: original insn 0xaaaaaaaa0894: 1f 20
03 d5      nop
[displaced] prepare: selected buffer at 0xaaaaaaaa0788
[displaced] prepare: saved 0xaaaaaaaa0788: 1e 00 80 d2
[displaced] aarch64_displaced_step_copy_insn: writing insn d503201f at
0xaaaaaaaa0788
[displaced] displaced_step_prepare_throw: prepared successfully
thread=1307111.1307111.0, original_pc=0xaaaaaaaa0894,
displaced_pc=0xaaaaaaaa0788
[displaced] displaced_step_prepare_throw: replacement insn 0xaaaaaaaa0788: 1f
20 03 d5   nop
[displaced] finish: restored 1307111.1307111.0 0xaaaaaaaa0788
[displaced] aarch64_displaced_step_fixup: PC after stepping: 0xaaaaaaaa0788
(was 0xaaaaaaaa0788).
[displaced] aarch64_displaced_step_fixup: adjusting PC by 4
[displaced] aarch64_displaced_step_fixup: PC did not move. Discarding PC
adjustment.
[displaced] aarch64_displaced_step_fixup: fixup: set PC to 0xaaaaaaaa0894:0

Breakpoint 5, pass () at
/home/linux/gdb/src/gdb/testsuite/gdb.arch/insn-reloc.c:31
31      }
+x /i $pc
=> 0xaaaaaaaa0894 <pass>:       nop
...

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[Bug tdep/31507] [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |luis.machado at arm dot com
          Component|gdb                         |tdep

--- Comment #7 from Tom de Vries <vries at gcc dot gnu.org> ---
This may be a regression due to:
...
commit 0c27188999bfc5bf03536bf44593c4ed8df296c3
Author: Luis Machado <luis.machado@linaro.org>
Date:   Thu Jan 9 16:04:36 2020 -0300

    Fix step-over-syscall.exp failure

    In particular, this one:

    FAIL: gdb.base/step-over-syscall.exp: fork: displaced=on:
check_pc_after_cross_syscall: single step over fork final pc

    When ptrace fork event reporting is enabled, GDB gets a PTRACE_EVENT_FORK
    event whenever the inferior executes the fork syscall.

    Then the logic is that GDB needs to step the inferior yet again in order to
    receive a predetermined SIGTRAP, but no execution takes place because the
    signal was already queued for delivery. That means the PC should stay the
same.

    I noticed the aarch64 code is currently adjusting the PC in this situation,
    making the inferior skip an instruction without executing it.

    The following change checks if we did not execute the instruction
    (pc - to == 0), making proper adjustments for such case.

    Regression tested on aarch64-linux-gnu on the tryserver.

    gdb/ChangeLog:

    2020-01-21  Luis Machado  <luis.machado@linaro.org>
...

Luis, could you take a look?

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[Bug tdep/31507] [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[luis.machado at arm dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

--- Comment #8 from Luis Machado <luis.machado at arm dot com> ---
Sure. I vaguely recall the situation with
0c27188999bfc5bf03536bf44593c4ed8df296c3

I'm wondering if we're incorrectly identifying an instruction that we're trying
to displaced-step and going through an incorrect outcome.

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[Bug tdep/31507] [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[luis.machado at arm dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

Luis Machado <luis.machado at arm dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED

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[Bug tdep/31507] [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[luis.machado at arm dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

--- Comment #9 from Luis Machado <luis.machado at arm dot com> ---
I tried running this test with RACY_ITER=100 but didn't see any FAIL's. It
comes out as non-racy.

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[Bug tdep/31507] [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[luis.machado at arm dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

--- Comment #10 from Luis Machado <luis.machado at arm dot com> ---
Ok. This doesn't reproduce for me even if I run it 1000 times.

I'll check the log file more thoroughly to see if anything rings a bell.

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[Bug tdep/31507] [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

--- Comment #11 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Luis Machado from comment #10)
> Ok. This doesn't reproduce for me even if I run it 1000 times.

That's unfortunate.

Let me try to describe the setup, in case that helps in any way:
- lenovo ideapad 3 chromebook, SOC mt8183 (4 Cortex-A73, 4 Cortex-A53), 4GB RAM
- debian 12, installed from
https://github.com/hexdump0815/imagebuilder/blob/main/systems/chromebook_kukui/readme.md
- system up-to-date
- uname -a: Linux changeme 6.1.51-stb-mt8+ #1 SMP PREEMPT
    Tue Sep  5 16:08:26 CEST 2023 aarch64 GNU/Linux
- ldd (Debian GLIBC 2.36-9+deb12u4) 2.36
- gcc version 12.2.0 (Debian 12.2.0-14) 
- GNU assembler (GNU Binutils for Debian) 2.40
- gdb build with -O0 -g -fuse-ld=mold
- build at commit 6549a232d25 ("Fix compiling bfd/vms-lib.c for a 32-bit
host.")

I tried my usual tricks of "taskset -c 0" and "stress -c 8", but found that
this makes the fail less likely.

I haven't been able to reproduce on either pinebook pro (running manjaro) or m1
macbook (running fedora asahi remix).

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[Bug tdep/31507] [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[luis.machado at arm dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

--- Comment #12 from Luis Machado <luis.machado at arm dot com> ---
Ok, that's useful information. Let me try to get the kernel + tools versions
right first, and then I'll make another attempt at reproducing things.

It is a bit suspicious that we're having an issue with a nop instruction. But
let me play with it some and see if I find anything.

As usual, the case the patch was trying to address was a bit odd.

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[Bug tdep/31507] [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

--- Comment #13 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Tom de Vries from comment #7)
> This may be a regression due to:
> ...
> commit 0c27188999bfc5bf03536bf44593c4ed8df296c3
> Author: Luis Machado <luis.machado@linaro.org>
> Date:   Thu Jan 9 16:04:36 2020 -0300
> 
>     Fix step-over-syscall.exp failure

I've confirmed this, ran a loop with 500 iterations, didn't fail before the
commit, fails after the commit.

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[Bug tdep/31507] [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[luis.machado at arm dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

--- Comment #14 from Luis Machado <luis.machado at arm dot com> ---
Thanks for confirming Tom.

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[Bug tdep/31507] [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[luis.machado at arm dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

--- Comment #15 from Luis Machado <luis.machado at arm dot com> ---
Just a quick update. I've tried this on different hardware with a newer Ubuntu
(22.04). I couldn't get it to reproduce yet.

I'm trying a few more things.

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[Bug tdep/31507] [gdb, aarch64] FAIL: gdb.arch/disp-step-insn-reloc.exp: can_relocate_adr_forward: relocated instruction

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31507

--- Comment #16 from Tom de Vries <vries at gcc dot gnu.org> ---
I've also ran into this with gdb.dwarf2/dw2-lines.exp.

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