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While reviewing the native AArch64 patch, I noticed a problem:
On 02/06/2013 08:46 PM, Pedro Alves wrote:
>
>> > +static void
>> > +aarch64_linux_prepare_to_resume (struct lwp_info *lwp)
>> > +{
>> > + struct arch_lwp_info *info = lwp->arch_private;
>> > +
>> > + /* NULL means this is the main thread still going through the shell,
>> > + or, no watchpoint has been set yet. In that case, there's
>> > + nothing to do. */
>> > + if (info == NULL)
>> > + return;
>> > +
>> > + if (DR_HAS_CHANGED (info->dr_changed_bp)
>> > + || DR_HAS_CHANGED (info->dr_changed_wp))
>> > + {
>> > + int tid = GET_LWP (lwp->ptid);
>> > + struct aarch64_debug_reg_state *state = aarch64_get_debug_reg_state ();
> Hmm. This is always fetching the debug_reg_state of
> the current inferior, but may not be the inferior of lwp.
> I see the same bug on x86. Sorry about that. I'll fix it.
A natural fix would be to make xxx_get_debug_reg_state take an
inferior argument, but that doesn't work because of the case where we
detach breakpoints/watchpoints from the child fork, at a time there's
no inferior for the child fork at all. We do a nasty hack in
i386_inferior_data_get, but that relies on all callers pointing the
current inferior to the correct inferior, which isn't actually being
done by all callers, and I don't think we want to enforce that -- deep
in the bowls of linux-nat.c, there are many cases we resume lwps
behind the scenes, and it's be better to not have that code rely on
global state (as it doesn't today).
The fix is to decouple the watchpoints code from inferiors, making it
track target processes instead. This way, we can freely keep track of
the watchpoint mirrors for these processes behind the core's back.
Checkpoints also play dirty tricks with swapping the process behind
the inferior, so they get special treatment too in the patch (which
just amounts to calling a new hook). Instead of the old hack in
i386_inferior_data_get, where we returned a copy of the current
inferior's debug registers mirror, as soon as we detect a fork in the
target, we copy the debug register mirror from the parent to the child
process.
I don't have an old kernel handy to test, but I stepped through gdb doing
the watchpoint removal in the fork child in the watchpoint-fork test
seeing that the debug registers end up cleared in the child.
I didn't find the need for linux_nat_iterate_watchpoint_lwps. If
we use plain iterate_over_lwps instead, what happens is that
when removing watchpoints, that iterate_over_lwps doesn't actually
iterate over anything, since the fork child is not added to the
lwp list until later, at detach time, in linux_child_follow_fork.
And if we don't iterate over that lwp, we don't mark its debug
registers as needing update. But linux_child_follow_fork takes
care of doing that explicitly:
child_lp = add_lwp (inferior_ptid);
child_lp->stopped = 1;
child_lp->last_resume_kind = resume_stop;
make_cleanup (delete_lwp_cleanup, child_lp);
/* CHILD_LP has new PID, therefore linux_nat_new_thread is not called for it.
See i386_inferior_data_get for the Linux kernel specifics.
Ensure linux_nat_prepare_to_resume will reset the hardware debug
registers. It is done by the linux_nat_new_thread call, which is
being skipped in add_lwp above for the first lwp of a pid. */
gdb_assert (num_lwps (GET_PID (child_lp->ptid)) == 1);
if (linux_nat_new_thread != NULL)
linux_nat_new_thread (child_lp);
if (linux_nat_prepare_to_resume != NULL)
linux_nat_prepare_to_resume (child_lp);
ptrace (PTRACE_DETACH, child_pid, 0, 0);
so unless I'm missing something (quite possible) it ends up all
the same. But, the !detach-on-fork, and the "follow-fork child" paths
should also call linux_nat_new_thread, and they don't presently. It
seems to me in those cases we're not clearing debug regs correctly
when that's needed. Instead of copying that bit that works around
add_lwp bypassing the linux_nat_new_thread call, I thought it'd
be better to add an add_initial_lwp call to be used in the case we
really need to bypass linux_nat_new_thread, and make
add_lwp always call linux_nat_new_thread.
i386_cleanup_dregs is rewritten to forget about the current process
debug mirrors, which takes cares of other i386 ports. Only a couple
of extra tweaks here and there were needed, as some targets wheren't
actually calling i386_cleanup_dregs.
Tested on Fedora 17 x86_64 -m64/-m32.
GDBserver already fetches the i386_debug_reg_state from the right
process, and, it doesn't handle forks at all, so no fix is needed over
there.
gdb/
2013-02-13 Pedro Alves <palves@redhat.com>
* amd64-linux-nat.c (update_debug_registers_callback):
Update comment.
(amd64_linux_dr_set_control, amd64_linux_dr_set_addr): Use
iterate_over_lwps.
(amd64_linux_prepare_to_resume): Pass the lwp's pid to
i386_debug_reg_state.
(amd64_linux_new_fork): New function.
(_initialize_amd64_linux_nat): Install amd64_linux_new_fork as
linux_nat_new_fork hook, and i386_forget_process as
linux_nat_forget_process hook.
* i386-linux-nat.c (update_debug_registers_callback):
Update comment.
(amd64_linux_dr_set_control, amd64_linux_dr_set_addr): Use
iterate_over_lwps.
(i386_linux_prepare_to_resume): Pass the lwp's pid to
i386_debug_reg_state.
(i386_linux_new_fork): New function.
(_initialize_i386_linux_nat): Install i386_linux_new_fork as
linux_nat_new_fork hook, and i386_forget_process as
linux_nat_forget_process hook.
* i386-nat.c (i386_init_dregs): Delete.
(i386_inferior_data, struct i386_inferior_data):
Delete.
(struct i386_process_info): New.
(i386_process_list): New global.
(i386_find_process_pid, i386_add_process, i386_process_info_get):
New functions.
(i386_inferior_data_get): Delete.
(i386_process_info_get): New function.
(i386_debug_reg_state): New parameter 'pid'. Reimplement.
(i386_forget_process): New function.
(i386_cleanup_dregs): Rewrite.
(i386_update_inferior_debug_regs, i386_insert_watchpoint)
(i386_remove_watchpoint, i386_region_ok_for_watchpoint)
(i386_stopped_data_address, i386_insert_hw_breakpoint)
(i386_remove_hw_breakpoint): Adjust to pass the current process id
to i386_debug_reg_state.
(i386_use_watchpoints): Don't register inferior data.
* i386-nat.h (i386_debug_reg_state): Add new 'pid' parameter, and
adjust comment.
(i386_forget_process): Declare.
* linux-fork.c (delete_fork): Call linux_nat_forget_process.
* linux-nat.c (linux_nat_new_fork, linux_nat_forget_process_hook):
New static globals.
(linux_child_follow_fork): Don't call linux_nat_new_thread here.
(add_initial_lwp): New, factored out from ...
(add_lwp): ... this. Don't check the number of lwps before
calling linux_nat_new_thread.
(linux_nat_iterate_watchpoint_lwps): Delete.
(linux_nat_attach): Use add_initial_lwp instead of add_lwp.
(linux_handle_extended_wait): Call the linux_nat_new_fork hook on
forks and vforks.
(linux_nat_wait_1): Use add_initial_lwp instead of add_lwp for the
initial lwp.
(linux_nat_kill, linux_nat_mourn_inferior): Call
linux_nat_forget_process.
(linux_nat_set_new_fork, linux_nat_set_forget_process)
(linux_nat_forget_process): New functions.
* linux-nat.h (linux_nat_iterate_watchpoint_lwps_ftype): Delete
type.
(linux_nat_iterate_watchpoint_lwps): Delete declaration.
(linux_nat_new_fork_ftype, linux_nat_forget_process_ftype): New
types.
(linux_nat_set_new_fork, linux_nat_set_forget_process)
(linux_nat_forget_process): New declarations.
* amd64fbsd-nat.c (super_mourn_inferior): New global.
(amd64fbsd_mourn_inferior): New function.
(_initialize_amd64fbsd_nat): Override to_mourn_inferior.
* windows-nat.c (windows_detach): Call i386_cleanup_dregs.
124 lines
4.3 KiB
C
124 lines
4.3 KiB
C
/* Native-dependent code for the i386.
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Low level functions to implement Oeprating System specific
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code to manipulate I386 debug registers.
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Copyright (C) 2009-2013 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#ifndef I386_NAT_H
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#define I386_NAT_H 1
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/* Hardware-assisted breakpoints and watchpoints. */
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/* Add watchpoint methods to the provided target_ops.
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Targets using i386 family debug registers for watchpoints should call
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this. */
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struct target_ops;
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extern void i386_use_watchpoints (struct target_ops *);
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/* Support for hardware watchpoints and breakpoints using the i386
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debug registers.
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This provides several functions for inserting and removing
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hardware-assisted breakpoints and watchpoints, testing if one or
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more of the watchpoints triggered and at what address, checking
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whether a given region can be watched, etc.
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In addition, each target should provide several low-level functions
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regrouped into i386_dr_low_type struct below. These functions
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that will be called to insert watchpoints and hardware breakpoints
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into the inferior, remove them, and check their status. These
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functions are:
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set_control -- set the debug control (DR7)
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register to a given value for all LWPs
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set_addr -- put an address into one debug
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register for all LWPs
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get_addr -- return the address in a given debug
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register of the current LWP
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get_status -- return the value of the debug
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status (DR6) register for current LWP
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get_control -- return the value of the debug
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control (DR7) register for current LWP
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Additionally, the native file should set the debug_register_length
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field to 4 or 8 depending on the number of bytes used for
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deubg registers. */
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struct i386_dr_low_type
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{
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void (*set_control) (unsigned long);
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void (*set_addr) (int, CORE_ADDR);
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CORE_ADDR (*get_addr) (int);
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unsigned long (*get_status) (void);
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unsigned long (*get_control) (void);
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int debug_register_length;
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};
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extern struct i386_dr_low_type i386_dr_low;
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/* Debug registers' indices. */
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#define DR_FIRSTADDR 0
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#define DR_LASTADDR 3
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#define DR_NADDR 4 /* The number of debug address registers. */
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#define DR_STATUS 6 /* Index of debug status register (DR6). */
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#define DR_CONTROL 7 /* Index of debug control register (DR7). */
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/* Global state needed to track h/w watchpoints. */
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struct i386_debug_reg_state
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{
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/* Mirror the inferior's DRi registers. We keep the status and
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control registers separated because they don't hold addresses.
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Note that since we can change these mirrors while threads are
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running, we never trust them to explain a cause of a trap.
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For that, we need to peek directly in the inferior registers. */
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CORE_ADDR dr_mirror[DR_NADDR];
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unsigned dr_status_mirror, dr_control_mirror;
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/* Reference counts for each debug register. */
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int dr_ref_count[DR_NADDR];
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};
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/* Use this function to set i386_dr_low debug_register_length field
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rather than setting it directly to check that the length is only
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set once. It also enables the 'maint set/show show-debug-regs'
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command. */
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extern void i386_set_debug_register_length (int len);
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/* Use this function to reset the i386-nat.c debug register state. */
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extern void i386_cleanup_dregs (void);
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/* Return a pointer to the local mirror of the debug registers of
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process PID. */
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extern struct i386_debug_reg_state *i386_debug_reg_state (pid_t pid);
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/* Called whenever GDB is no longer debugging process PID. It deletes
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data structures that keep track of debug register state. */
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extern void i386_forget_process (pid_t pid);
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#endif /* I386_NAT_H */
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