[Bug 1934505]

Thu Jul 8 14:05:11 UTC 2021

The master branch has been updated by Simon Marchi
<simark at sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-
gdb.git;h=74b10a3219e44ba2585e3f7226a6455d41e92c1b

commit 74b10a3219e44ba2585e3f7226a6455d41e92c1b
Author: Simon Marchi <simon.marchi at polymtl.ca>
Date:   Wed Jul 7 08:57:36 2021 -0400

    gdb: don't set Linux-specific displaced stepping methods in s390_gdbarch_init

    According to bug 28056, running an s390x binary gives:

        (gdb) run
        Starting program: /usr/bin/ls
        /home/ubuntu/tmp/gdb-11.0.90.20210705/gdb/linux-tdep.c:2550: internal-error: displaced_step_prepare_status linux_displaced_step_prepare(gdbarch*, thread_info*, CORE_ADDR&): Assertion `gdbarch_data->num_disp_step_buffers > 0' failed.

    This is because the s390 architecture registers some Linux-specific
    displaced stepping callbacks in the OS-agnostic s390_gdbarch_init:

        set_gdbarch_displaced_step_prepare (gdbarch, linux_displaced_step_prepare);
        set_gdbarch_displaced_step_finish (gdbarch, linux_displaced_step_finish);
        set_gdbarch_displaced_step_restore_all_in_ptid
          (gdbarch, linux_displaced_step_restore_all_in_ptid);

    But then the Linux-specific s390_linux_init_abi_any passes
    num_disp_step_buffers=0 to linux_init_abi:

        linux_init_abi (info, gdbarch, 0);

    The problem happens when linux_displaced_step_prepare is called for the
    first time.  It tries to allocate the displaced stepping buffers, but
    sees that the number of displaced stepping buffers for that architecture
    is 0, which is unexpected / invalid.

    s390_gdbarch_init should not register the linux_* callbacks, that is
    expected to be done by linux_init_abi.  If debugging a bare-metal s390
    program, or an s390 program on another OS GDB doesn't know about, we
    wouldn't want to use them.  We would either register no callbacks, if
    displaced stepping isn't supported, or register a different set of
    callbacks if we wanted to support displaced stepping in those cases.

    The commit that refactored the displaced stepping machinery and
    introduced these set_gdbarch_displaced_step_* calls is 187b041e2514
    ("gdb: move displaced stepping logic to gdbarch, allow starting
    concurrent displaced steps").  However, even before that,
    s390_gdbarch_init did:

      set_gdbarch_displaced_step_location (gdbarch, linux_displaced_step_location);

    ... which already seemed wrong.  The Linux-specific callback was used
    even for non-Linux system.  Maybe that was on purpose, because it would
    also happen to work in some other non-Linux case, or maybe it was simply
    a mistake.  I'll assume that this was a small mistake when
    s390-tdep.{h,c} where factored out of s390-linux-tdep.c, in d6e589456475
    ("s390: Split up s390-linux-tdep.c into two files").

    Fix this by removing the setting of these displaced step callbacks from
    s390_gdbarch_init.  Instead, pass num_disp_step_buffers=1 to
    linux_init_abi, in s390_linux_init_abi_any.  Doing so will cause
    linux_init_abi to register these same callbacks.  It will also mean that
    when debugging a bare-metal s390 executable or an executable on another
    OS that GDB doesn't know about, gdbarch_displaced_step_prepare won't be
    set, so displaced stepping won't be used.

    This patch will need to be merged in the gdb-11-branch, since this is a
    GDB 11 regression, so here's the ChangeLog entry:

    gdb/ChangeLog:

            * s390-linux-tdep.c (s390_linux_init_abi_any): Pass 1 (number
            of displaced stepping buffers to linux_init_abi.
            * s390-tdep.c (s390_gdbarch_init): Don't set the Linux-specific
            displaced-stepping gdbarch callbacks.

    Change-Id: Ieab2f8990c78fde845ce7378d6fd4ee2833800d5
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28056

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https://bugs.launchpad.net/bugs/1934505

Title:
  gdb 11 doesn't work on impish/s390x: internal-error:
  displaced_step_prepare_status linux_displaced_step_prepare(gdbarch*,
  thread_info*, CORE_ADDR&): Assertion
  `gdbarch_data->num_disp_step_buffers > 0' failed.

Status in gdb:
  Confirmed
Status in gdb package in Ubuntu:
  Fix Released

Bug description:
  gdb doesn't work on impish/s390x at the minute. Even if you say 'no'
  to both questions you still can't debug:

  ubuntu at laney-bos01-s390x-2:~/glib-networking-2.66.0/build$ gdb ls
  GNU gdb (Ubuntu 11.0.50.20210630-0ubuntu1) 11.0.50.20210630-git
  Copyright (C) 2021 Free Software Foundation, Inc.
  License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
  This is free software: you are free to change and redistribute it.
  There is NO WARRANTY, to the extent permitted by law.
  Type "show copying" and "show warranty" for details.
  This GDB was configured as "s390x-linux-gnu".
  Type "show configuration" for configuration details.
  For bug reporting instructions, please see:
  <https://www.gnu.org/software/gdb/bugs/>.
  Find the GDB manual and other documentation resources online at:
      <http://www.gnu.org/software/gdb/documentation/>.

  For help, type "help".
  Type "apropos word" to search for commands related to "word"...
  Reading symbols from ls...
  (No debugging symbols found in ls)
  (gdb) run
  Starting program: /usr/bin/ls
  /build/gdb-Ti35un/gdb-11.0.50.20210630/gdb/linux-tdep.c:2550: internal-error: displaced_step_prepare_status linux_displaced_step_prepare(gdbarch*, thread_info*, CORE_ADDR&): Assertion `gdbarch_data->num_disp_step_buffers > 0' failed.
  A problem internal to GDB has been detected,
  further debugging may prove unreliable.
  Quit this debugging session? (y or n) n

  This is a bug, please report it.  For instructions, see:
  <https://www.gnu.org/software/gdb/bugs/>.

  /build/gdb-Ti35un/gdb-11.0.50.20210630/gdb/linux-tdep.c:2550: internal-error: displaced_step_prepare_status linux_displaced_step_prepare(gdbarch*, thread_info*, CORE_ADDR&): Assertion `gdbarch_data->num_disp_step_buffers > 0' failed.
  A problem internal to GDB has been detected,
  further debugging may prove unreliable.
  Create a core file of GDB? (y or n) n
  Command aborted.
  (gdb)

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