Re: [PING][PATCH v2 PR gdb/21870] aarch64: Leftover uncleared debug registers

Wei-min Pan
2019-02-06T22:36:20Z

On 2/6/2019 4:43 AM, Alan Hayward wrote:
>
>
>> On 6 Feb 2019, at 00:51, Weimin Pan <weimin.pan@oracle.com> wrote:
>>
>> Would you please review this aarch64-specific patch? Thanks.
>
>
> Had a few problems applying the patch directly.
> Also, the changelog entry should be in the body of the email and not
> the patch.

Thanks for pointing it out, noted.

> But, ignoring that for now...
>
> I ran the test case with the current HEAD on AArch64, and it passed.
> I think that your issue might have already been fixed with the following
> patch:
>
> commit 754e31689866524049b9cfc68053ed4e1293cfac
> Author: Alan Hayward <alan.hayward@arm.com>
> Date:Â Â  9 weeks ago
>
>Â Â Â Â  AArch64: Racy: Don't set empty set of hardware BPs/WPs on new thread
>
>
> My patch is roughly doing the same thing, but in a different way.
> Could you check this please?

Yes, your patch does fix the problem.

>
> I've not yet read the test case in detail. If the bug is already fixed,
> then the test might still be useful.

I can push the test, which is included in the bug report, upstream.

Thanks.

> Alan.
>
>
>> On 7/11/2018 5:30 PM, Wei-min Pan wrote:
>>> On 6/27/2018 6:10 PM, Weimin Pan wrote:
>>>> At issue here is that ptrace() does not validate either address or size
>>>> when setting a hardware watchpoint/breakpoint. As a result, watchpoints
>>>> were set at address 0, the initial value of aarch64_debug_reg_state in
>>>> aarch64_process_info, and DR_CONTROL_LENGTH (dreg_state.dbg_regs[i].ctrl)
>>>> got changed to a non-zero default value, when the PTRACE_SETREGSET request
>>>> was made in aarch64_linux_set_debug_regs(), in preparation for resuming
>>>> the thread.
>>>>
>>>> I sent out a patch upstream for review last year. Yao Qi commented that
>>>> he needed to take a look at ptrace implementation to better understand
>>>> why this was happening. Unfortunately he didn't get a chance to do so.
>>>>
>>>> This is a revised patch which calls ptrace only if any debug register
>>>> has changed, either address or control containing a non-zero value,
>>>> in aarch64_linux_set_debug_regs() and is similar to what x86 does -
>>>> x86_linux_update_debug_registers() checks if a debug register has
>>>> non-zero reference count before setting it.
>>>>
>>>> Tested on aarch64-linux-gnu. No regressions.
>>>> ---
>>>> gdb/ChangeLog | 6 +
>>>> gdb/nat/aarch64-linux-hw-point.c | 7 +
>>>> gdb/testsuite/ChangeLog | 20 ++-
>>>> gdb/testsuite/gdb.arch/aarch64-dbreg-contents.c | 179 ++++++++++++++++++++++
>>>> gdb/testsuite/gdb.arch/aarch64-dbreg-contents.exp | 40 +++++
>>>> 5 files changed, 244 insertions(+), 8 deletions(-)
>>>> create mode 100644 gdb/testsuite/gdb.arch/aarch64-dbreg-contents.c
>>>> create mode 100644 gdb/testsuite/gdb.arch/aarch64-dbreg-contents.exp
>>>>
>>>> diff --git a/gdb/ChangeLog b/gdb/ChangeLog
>>>> index 7b108bf..d5bf15f 100644
>>>> --- a/gdb/ChangeLog
>>>> +++ b/gdb/ChangeLog
>>>> @@ -1,3 +1,9 @@
>>>> +2018-06-27 Weimin Pan <weimin.pan@oracle.com>
>>>> +
>>>> + PR gdb/21870
>>>> + * nat/aarch64-linux-hw-point.c (aarch64_linux_set_debug_regs):
>>>> + Validate debug register contents before calling ptrace.
>>>> +
>>>> 2018-06-18 Tom Tromey <tom@tromey.com>
>>>> * solib-aix.c (solib_aix_get_section_offsets): Return
>>>> diff --git a/gdb/nat/aarch64-linux-hw-point.c b/gdb/nat/aarch64-linux-hw-point.c
>>>> index a3931ea..41ac304 100644
>>>> --- a/gdb/nat/aarch64-linux-hw-point.c
>>>> +++ b/gdb/nat/aarch64-linux-hw-point.c
>>>> @@ -694,11 +694,18 @@ aarch64_linux_set_debug_regs (struct aarch64_debug_reg_state *state,
>>>> iov.iov_len = (offsetof (struct user_hwdebug_state, dbg_regs)
>>>> + count * sizeof (regs.dbg_regs[0]));
>>>> + int changed_regs = 0;
>>>> for (i = 0; i < count; i++)
>>>> {
>>>> regs.dbg_regs[i].addr = addr[i];
>>>> regs.dbg_regs[i].ctrl = ctrl[i];
>>>> + /* Check to see if any of these debug registers contains valid data,
>>>> + e.g. non-zero, before calling ptrace. See PR gdb/21870. */
>>>> + if (ctrl[i] || addr[i])
>>>> + changed_regs++;
>>>> }
>>>> + if (changed_regs == 0)
>>>> + return;
>>>> if (ptrace (PTRACE_SETREGSET, tid,
>>>> watchpoint ? NT_ARM_HW_WATCH : NT_ARM_HW_BREAK,
>>>> diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
>>>> index a812061..0ce2d34 100644
>>>> --- a/gdb/testsuite/ChangeLog
>>>> +++ b/gdb/testsuite/ChangeLog
>>>> @@ -1,4 +1,9 @@
>>>> +2018-06-27 Weimin Pan <weimin.pan@oracle.com>
>>>> +
>>>> + PR gdb/21870
>>>> + * gdb.arch/aarch64-dbreg-contents.c: New file.
>>>> + * gdb.arch/aarch64-dbreg-contents.exp: New file.
>>>> +
>>>> 2018-06-18 Tom de Vries <tdevries@suse.de>
>>>> * gdb.ada/bp_inlined_func.exp: Allow 5 breakpoint locations.
>>>> diff --git a/gdb/testsuite/gdb.arch/aarch64-dbreg-contents.c b/gdb/testsuite/gdb.arch/aarch64-dbreg-contents.c
>>>> new file mode 100644
>>>> index 0000000..85d4a03
>>>> --- /dev/null
>>>> +++ b/gdb/testsuite/gdb.arch/aarch64-dbreg-contents.c
>>>> @@ -0,0 +1,179 @@
>>>> +/* Test case for setting a memory-write unaligned watchpoint on aarch64.
>>>> +
>>>> + This software is provided 'as-is', without any express or implied
>>>> + warranty. In no event will the authors be held liable for any damages
>>>> + arising from the use of this software.
>>>> +
>>>> + Permission is granted to anyone to use this software for any purpose,
>>>> + including commercial applications, and to alter it and redistribute it
>>>> + freely. */
>>>> +
>>>> +#define _GNU_SOURCE 1
>>>> +#ifdef __ia64__
>>>> +#define ia64_fpreg ia64_fpreg_DISABLE
>>>> +#define pt_all_user_regs pt_all_user_regs_DISABLE
>>>> +#endif /* __ia64__ */
>>>> +#include <sys/ptrace.h>
>>>> +#ifdef __ia64__
>>>> +#undef ia64_fpreg
>>>> +#undef pt_all_user_regs
>>>> +#endif /* __ia64__ */
>>>> +#include <linux/ptrace.h>
>>>> +#include <sys/types.h>
>>>> +#include <sys/user.h>
>>>> +#if defined __i386__ || defined __x86_64__
>>>> +#include <sys/debugreg.h>
>>>> +#endif
>>>> +
>>>> +#include <assert.h>
>>>> +#include <unistd.h>
>>>> +#include <sys/wait.h>
>>>> +#include <stdio.h>
>>>> +#include <stdlib.h>
>>>> +#include <stddef.h>
>>>> +#include <errno.h>
>>>> +#include <sys/uio.h>
>>>> +#include <elf.h>
>>>> +#include <error.h>
>>>> +
>>>> +static __attribute__((unused)) pid_t child;
>>>> +
>>>> +static __attribute__((unused)) void
>>>> +cleanup (void)
>>>> +{
>>>> + if (child > 0)
>>>> + kill (child, SIGKILL);
>>>> + child = 0;
>>>> +}
>>>> +
>>>> +static __attribute__((unused)) void
>>>> +handler_fail (int signo)
>>>> +{
>>>> + cleanup ();
>>>> + signal (signo, SIG_DFL);
>>>> + raise (signo);
>>>> +}
>>>> +
>>>> +#ifdef __aarch64__
>>>> +
>>>> +#define SET_WATCHPOINT set_watchpoint
>>>> +
>>>> +/* Macros to extract fields from the hardware debug information word. */
>>>> +#define AARCH64_DEBUG_NUM_SLOTS(x) ((x) & 0xff)
>>>> +#define AARCH64_DEBUG_ARCH(x) (((x) >> 8) & 0xff)
>>>> +/* Macro for the expected version of the ARMv8-A debug architecture. */
>>>> +#define AARCH64_DEBUG_ARCH_V8 0x6
>>>> +#define DR_CONTROL_ENABLED(ctrl) (((ctrl) & 0x1) == 1)
>>>> +#define DR_CONTROL_LENGTH(ctrl) (((ctrl) >> 5) & 0xff)
>>>> +
>>>> +static void
>>>> +set_watchpoint (pid_t pid, volatile void *addr, unsigned len_mask)
>>>> +{
>>>> + struct user_hwdebug_state dreg_state;
>>>> + struct iovec iov;
>>>> + long l;
>>>> +
>>>> + assert (len_mask >= 0x01);
>>>> + assert (len_mask <= 0xff);
>>>> +
>>>> + iov.iov_base = &dreg_state;
>>>> + iov.iov_len = sizeof (dreg_state);
>>>> + errno = 0;
>>>> + l = ptrace (PTRACE_GETREGSET, pid, NT_ARM_HW_WATCH, &iov);
>>>> + assert (l == 0);
>>>> + assert (AARCH64_DEBUG_ARCH (dreg_state.dbg_info) == AARCH64_DEBUG_ARCH_V8);
>>>> + assert (AARCH64_DEBUG_NUM_SLOTS (dreg_state.dbg_info) >= 1);
>>>> +
>>>> + assert (!DR_CONTROL_ENABLED (dreg_state.dbg_regs[0].ctrl));
>>>> + dreg_state.dbg_regs[0].ctrl |= 1;
>>>> + assert ( DR_CONTROL_ENABLED (dreg_state.dbg_regs[0].ctrl));
>>>> +
>>>> + assert (DR_CONTROL_LENGTH (dreg_state.dbg_regs[0].ctrl) == 0);
>>>> + dreg_state.dbg_regs[0].ctrl |= len_mask << 5;
>>>> + assert (DR_CONTROL_LENGTH (dreg_state.dbg_regs[0].ctrl) == len_mask);
>>>> +
>>>> + dreg_state.dbg_regs[0].ctrl |= 2 << 3; // write
>>>> + dreg_state.dbg_regs[0].ctrl |= 2 << 1; // GDB: ???: enabled at el0
>>>> + //printf("ctrl=0x%x\n",dreg_state.dbg_regs[0].ctrl);
>>>> + dreg_state.dbg_regs[0].addr = (uintptr_t) addr;
>>>> +
>>>> + iov.iov_base = &dreg_state;
>>>> + iov.iov_len = (offsetof (struct user_hwdebug_state, dbg_regs)
>>>> + + sizeof (dreg_state.dbg_regs[0]));
>>>> + errno = 0;
>>>> + l = ptrace (PTRACE_SETREGSET, pid, NT_ARM_HW_WATCH, &iov);
>>>> + if (errno != 0)
>>>> + error (1, errno, "PTRACE_SETREGSET: NT_ARM_HW_WATCH");
>>>> + assert (l == 0);
>>>> +}
>>>> +
>>>> +#endif
>>>> +
>>>> +#ifndef SET_WATCHPOINT
>>>> +
>>>> +int
>>>> +main (void)
>>>> +{
>>>> + return 77;
>>>> +}
>>>> +#else
>>>> +
>>>> +static volatile long long check;
>>>> +
>>>> +int
>>>> +main (void)
>>>> +{
>>>> + pid_t got_pid;
>>>> + int i, status;
>>>> + long l;
>>>> +
>>>> + atexit (cleanup);
>>>> + signal (SIGABRT, handler_fail);
>>>> + signal (SIGINT, handler_fail);
>>>> +
>>>> + child = fork ();
>>>> + assert (child >= 0);
>>>> + if (child == 0)
>>>> + {
>>>> + l = ptrace (PTRACE_TRACEME, 0, NULL, NULL);
>>>> + assert (l == 0);
>>>> + i = raise (SIGUSR1);
>>>> + assert (i == 0);
>>>> + check = -1;
>>>> + i = raise (SIGUSR2);
>>>> + /* NOTREACHED */
>>>> + assert (0);
>>>> + }
>>>> +
>>>> + got_pid = waitpid (child, &status, 0);
>>>> + assert (got_pid == child);
>>>> + assert (WIFSTOPPED (status));
>>>> + assert (WSTOPSIG (status) == SIGUSR1);
>>>> +
>>>> + // PASS:
>>>> + //SET_WATCHPOINT (child, &check, 0xff);
>>>> + // FAIL:
>>>> + SET_WATCHPOINT (child, &check, 0x02);
>>>> +
>>>> + errno = 0;
>>>> + l = ptrace (PTRACE_CONT, child, 0l, 0l);
>>>> + assert_perror (errno);
>>>> + assert (l == 0);
>>>> +
>>>> + got_pid = waitpid (child, &status, 0);
>>>> + assert (got_pid == child);
>>>> + assert (WIFSTOPPED (status));
>>>> + if (WSTOPSIG (status) == SIGUSR2)
>>>> + {
>>>> + /* We missed the watchpoint - unsupported by hardware? */
>>>> + cleanup ();
>>>> + return 2;
>>>> + }
>>>> + assert (WSTOPSIG (status) == SIGTRAP);
>>>> +
>>>> + cleanup ();
>>>> + return 0;
>>>> +}
>>>> +
>>>> +#endif
>>>> +
>>>> diff --git a/gdb/testsuite/gdb.arch/aarch64-dbreg-contents.exp b/gdb/testsuite/gdb.arch/aarch64-dbreg-contents.exp
>>>> new file mode 100644
>>>> index 0000000..6aa23b0
>>>> --- /dev/null
>>>> +++ b/gdb/testsuite/gdb.arch/aarch64-dbreg-contents.exp
>>>> @@ -0,0 +1,40 @@
>>>> +# Copyright 2018 Free Software Foundation, Inc.
>>>> +
>>>> +# This program is free software; you can redistribute it and/or modify
>>>> +# it under the terms of the GNU General Public License as published by
>>>> +# the Free Software Foundation; either version 3 of the License, or
>>>> +# (at your option) any later version.
>>>> +#
>>>> +# This program is distributed in the hope that it will be useful,
>>>> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
>>>> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>>>> +# GNU General Public License for more details.
>>>> +#
>>>> +# You should have received a copy of the GNU General Public License
>>>> +# along with this program. If not, see <http://www.gnu.org/licenses/>.
>>>> +#
>>>> +# Make sure that the inferior doesn't assert and exits successfully.
>>>> +
>>>> +if {![is_aarch64_target]} {
>>>> + verbose "Skipping ${gdb_test_file_name}."
>>>> + return
>>>> +}
>>>> +
>>>> +standard_testfile .c
>>>> +
>>>> +if { [gdb_compile ${srcdir}/${subdir}/${srcfile} ${binfile} executable {debug}] != "" } {
>>>> + untested "failed to compile"
>>>> + return -1
>>>> +}
>>>> +
>>>> +clean_restart $testfile
>>>> +
>>>> +set test "run to exit"
>>>> +gdb_test_multiple "run" "$test" {
>>>> + -re "exited with code 01.*$gdb_prompt $" {
>>>> + pass "$test"
>>>> + }
>>>> + -re "exited normally.*$gdb_prompt $" {
>>>> + pass "$test"
>>>> + }
>>>> +}