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

Alan Hayward
2019-02-06T12:43:39Z

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> 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.
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: 9 weeks ago

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?

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

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"
>>> + }
>>> +}
>>

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