[PATCH v4 5/7] Arch-specific remote follow fork

Don Breazeal
2015-01-25T21:49:25Z

This patch implements the architecture-specific pieces of follow-fork
for remote and extended-remote Linux targets, which in the current
implementation copyies the parent's debug register state into the new
child's data structures. This is required for x86, arm, aarch64, and
mips.

This follows the native implementation as closely as possible by
implementing a new linux_target_ops function 'new_fork', which is
analogous to 'linux_nat_new_fork' in linux-nat.c. In gdbserver, the debug
registers are stored in the process list, instead of an
architecture-specific list, so the function arguments are process_info
pointers instead of an lwp_info and a pid as in the native implementation.

In the MIPS implementation the debug register mirror is stored differently
from x86, ARM, and aarch64, so instead of doing a simple structure assignment
I had to clone the list of watchpoint structures.

Tested using gdb.threads/watchpoint-fork.exp on x86, and ran manual tests
on a MIPS board and an ARM board.

I don't currently have access to an aarch64 board, so if someone is able
to test this easily, please do.

Thanks
--Don

gdb/gdbserver/
2015-01-25 Don Breazeal <donb@codesourcery.com>

* linux-aarch64-low.c (aarch64_linux_new_fork): New function.
(the_low_target) <new_fork>: Initialize new member.
* linux-arm-low.c (arm_new_fork): New function.
(the_low_target) <new_fork>: Initialize new member.
* linux-low.c (handle_extended_wait): Call new target function
new_fork.
* linux-low.h (struct linux_target_ops) <new_fork>: New member.
* linux-mips-low.c (mips_add_watchpoint): New function
extracted from mips_insert_point.
(the_low_target) <new_fork>: Initialize new member.
(mips_linux_new_fork): New function.
(mips_insert_point): Call mips_add_watchpoint.
* linux-x86-low.c (x86_linux_new_fork): New function.
(the_low_target) <new_fork>: Initialize new member.

---
gdb/gdbserver/linux-aarch64-low.c | 28 +++++++++++++
gdb/gdbserver/linux-arm-low.c | 42 ++++++++++++++++++++
gdb/gdbserver/linux-low.c | 4 ++
gdb/gdbserver/linux-low.h | 3 +
gdb/gdbserver/linux-mips-low.c | 76 +++++++++++++++++++++++++++++++------
gdb/gdbserver/linux-x86-low.c | 29 ++++++++++++++
6 files changed, 170 insertions(+), 12 deletions(-)

diff --git a/gdb/gdbserver/linux-aarch64-low.c b/gdb/gdbserver/linux-aarch64-low.c
index 6b84042..f0cd339 100644
--- a/gdb/gdbserver/linux-aarch64-low.c
+++ b/gdb/gdbserver/linux-aarch64-low.c
@@ -1135,6 +1135,33 @@ aarch64_linux_new_thread (void)
return info;
}

+static void
+aarch64_linux_new_fork (struct process_info *parent,
+ struct process_info *child)
+{
+ /* These are allocated by linux_add_process. */
+ gdb_assert (parent->private != NULL
+ && parent->private->arch_private != NULL);
+ gdb_assert (child->private != NULL
+ && child->private->arch_private != NULL);
+
+ /* Linux kernel before 2.6.33 commit
+ 72f674d203cd230426437cdcf7dd6f681dad8b0d
+ will inherit hardware debug registers from parent
+ on fork/vfork/clone. Newer Linux kernels create such tasks with
+ zeroed debug registers.
+
+ GDB core assumes the child inherits the watchpoints/hw
+ breakpoints of the parent, and will remove them all from the
+ forked off process. Copy the debug registers mirrors into the
+ new process so that all breakpoints and watchpoints can be
+ removed together. The debug registers mirror will become zeroed
+ in the end before detaching the forked off process, thus making
+ this compatible with older Linux kernels too. */
+
+ *child->private->arch_private = *parent->private->arch_private;
+}
+
/* Called when resuming a thread.
If the debug regs have changed, update the thread's copies. */

@@ -1299,6 +1326,7 @@ struct linux_target_ops the_low_target =
NULL,
aarch64_linux_new_process,
aarch64_linux_new_thread,
+ aarch64_linux_new_fork,
aarch64_linux_prepare_to_resume,
};

diff --git a/gdb/gdbserver/linux-arm-low.c b/gdb/gdbserver/linux-arm-low.c
index 303d9c8..97f3848 100644
--- a/gdb/gdbserver/linux-arm-low.c
+++ b/gdb/gdbserver/linux-arm-low.c
@@ -717,6 +717,47 @@ arm_new_thread (void)
return info;
}

+static void
+arm_new_fork (struct process_info *parent, struct process_info *child)
+{
+ struct arch_process_info *parent_proc_info = parent->private->arch_private;
+ struct arch_process_info *child_proc_info = child->private->arch_private;
+ struct lwp_info *child_lwp;
+ struct arch_lwp_info *child_lwp_info;
+ int i;
+
+ /* These are allocated by linux_add_process. */
+ gdb_assert (parent->private != NULL
+ && parent->private->arch_private != NULL);
+ gdb_assert (child->private != NULL
+ && child->private->arch_private != NULL);
+
+ /* Linux kernel before 2.6.33 commit
+ 72f674d203cd230426437cdcf7dd6f681dad8b0d
+ will inherit hardware debug registers from parent
+ on fork/vfork/clone. Newer Linux kernels create such tasks with
+ zeroed debug registers.
+
+ GDB core assumes the child inherits the watchpoints/hw
+ breakpoints of the parent, and will remove them all from the
+ forked off process. Copy the debug registers mirrors into the
+ new process so that all breakpoints and watchpoints can be
+ removed together. The debug registers mirror will become zeroed
+ in the end before detaching the forked off process, thus making
+ this compatible with older Linux kernels too. */
+
+ *child_proc_info = *parent_proc_info;
+
+ /* Mark all the hardware breakpoints and watchpoints as changed to
+ make sure that the registers will be updated. */
+ child_lwp = find_lwp_pid (ptid_of (child));
+ child_lwp_info = child_lwp->arch_private;
+ for (i = 0; i < MAX_BPTS; i++)
+ child_lwp_info->bpts_changed[i] = 1;
+ for (i = 0; i < MAX_WPTS; i++)
+ child_lwp_info->wpts_changed[i] = 1;
+}
+
/* Called when resuming a thread.
If the debug regs have changed, update the thread's copies. */
static void
@@ -920,6 +961,7 @@ struct linux_target_ops the_low_target = {
NULL, /* siginfo_fixup */
arm_new_process,
arm_new_thread,
+ arm_new_fork,
arm_prepare_to_resume,
};

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 6feebd0..5af02ac 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -445,6 +445,10 @@ handle_extended_wait (struct lwp_info *event_child, int wstat)
child_proc->tdesc = tdesc;
child_lwp->must_set_ptrace_flags = 1;

+ /* Clone arch-specific process data. */
+ if (the_low_target.new_fork != NULL)
+ the_low_target.new_fork (parent_proc, child_proc);
+
/* Save fork info in the parent thread. */
event_thr->pending_follow.kind = TARGET_WAITKIND_FORKED;
event_thr->pending_follow.value.related_pid = ptid;
diff --git a/gdb/gdbserver/linux-low.h b/gdb/gdbserver/linux-low.h
index bea4a37..e65fb35 100644
--- a/gdb/gdbserver/linux-low.h
+++ b/gdb/gdbserver/linux-low.h
@@ -185,6 +185,9 @@ struct linux_target_ops
allocate it here. */
struct arch_lwp_info * (*new_thread) (void);

+ /* Hook to call, if any, when a new fork is attached. */
+ void (*new_fork) (struct process_info *parent, struct process_info *child);
+
/* Hook to call prior to resuming a thread. */
void (*prepare_to_resume) (struct lwp_info *);

diff --git a/gdb/gdbserver/linux-mips-low.c b/gdb/gdbserver/linux-mips-low.c
index 478bb6e..500cf3e 100644
--- a/gdb/gdbserver/linux-mips-low.c
+++ b/gdb/gdbserver/linux-mips-low.c
@@ -344,6 +344,68 @@ mips_linux_new_thread (void)
return info;
}

+/* Create a new mips_watchpoint and add it to the list. */
+
+static void
+mips_add_watchpoint (struct arch_process_info *private, CORE_ADDR addr,
+ int len, int watch_type)
+{
+ struct mips_watchpoint *new_watch;
+ struct mips_watchpoint **pw;
+
+ new_watch = xmalloc (sizeof (struct mips_watchpoint));
+ new_watch->addr = addr;
+ new_watch->len = len;
+ new_watch->type = watch_type;
+ new_watch->next = NULL;
+
+ pw = &private->current_watches;
+ while (*pw != NULL)
+ pw = &(*pw)->next;
+ *pw = new_watch;
+}
+
+/* Hook to call when a new fork is attached. */
+
+static void
+mips_linux_new_fork (struct process_info *parent,
+ struct process_info *child)
+{
+ struct arch_process_info *parent_private;
+ struct arch_process_info *child_private;
+ struct mips_watchpoint *wp;
+
+ /* These are allocated by linux_add_process. */
+ gdb_assert (parent->private != NULL
+ && parent->private->arch_private != NULL);
+ gdb_assert (child->private != NULL
+ && child->private->arch_private != NULL);
+
+ /* Linux kernel before 2.6.33 commit
+ 72f674d203cd230426437cdcf7dd6f681dad8b0d
+ will inherit hardware debug registers from parent
+ on fork/vfork/clone. Newer Linux kernels create such tasks with
+ zeroed debug registers.
+
+ GDB core assumes the child inherits the watchpoints/hw
+ breakpoints of the parent, and will remove them all from the
+ forked off process. Copy the debug registers mirrors into the
+ new process so that all breakpoints and watchpoints can be
+ removed together. The debug registers mirror will become zeroed
+ in the end before detaching the forked off process, thus making
+ this compatible with older Linux kernels too. */
+
+ parent_private = parent->private->arch_private;
+ child_private = child->private->arch_private;
+
+ child_private->watch_readback_valid = parent_private->watch_readback_valid;
+ child_private->watch_readback = parent_private->watch_readback;
+
+ for (wp = parent_private->current_watches; wp != NULL; wp = wp->next)
+ mips_add_watchpoint (child_private, wp->addr, wp->len, wp->type);
+
+ child_private->watch_mirror = parent_private->watch_mirror;
+}
/* This is the implementation of linux_target_ops method
prepare_to_resume. If the watch regs have changed, update the
thread's copies. */
@@ -397,8 +459,6 @@ mips_insert_point (enum raw_bkpt_type type, CORE_ADDR addr,
struct process_info *proc = current_process ();
struct arch_process_info *private = proc->private->arch_private;
struct pt_watch_regs regs;
- struct mips_watchpoint *new_watch;
- struct mips_watchpoint **pw;
int pid;
long lwpid;
enum target_hw_bp_type watch_type;
@@ -425,16 +485,7 @@ mips_insert_point (enum raw_bkpt_type type, CORE_ADDR addr,
return -1;

/* It fit. Stick it on the end of the list. */
- new_watch = xmalloc (sizeof (struct mips_watchpoint));
- new_watch->addr = addr;
- new_watch->len = len;
- new_watch->type = watch_type;
- new_watch->next = NULL;
-
- pw = &private->current_watches;
- while (*pw != NULL)
- pw = &(*pw)->next;
- *pw = new_watch;
+ mips_add_watchpoint (private, addr, len, watch_type);

private->watch_mirror = regs;

@@ -845,6 +896,7 @@ struct linux_target_ops the_low_target = {
NULL, /* siginfo_fixup */
mips_linux_new_process,
mips_linux_new_thread,
+ mips_linux_new_fork,
mips_linux_prepare_to_resume
};

diff --git a/gdb/gdbserver/linux-x86-low.c b/gdb/gdbserver/linux-x86-low.c
index 2c3fccc..b7138e9 100644
--- a/gdb/gdbserver/linux-x86-low.c
+++ b/gdb/gdbserver/linux-x86-low.c
@@ -768,6 +768,34 @@ x86_linux_new_thread (void)
return info;
}

+/* Target routine for linux_new_fork. */
+
+static void
+x86_linux_new_fork (struct process_info *parent, struct process_info *child)
+{
+ /* These are allocated by linux_add_process. */
+ gdb_assert (parent->private != NULL
+ && parent->private->arch_private != NULL);
+ gdb_assert (child->private != NULL
+ && child->private->arch_private != NULL);
+
+ /* Linux kernel before 2.6.33 commit
+ 72f674d203cd230426437cdcf7dd6f681dad8b0d
+ will inherit hardware debug registers from parent
+ on fork/vfork/clone. Newer Linux kernels create such tasks with
+ zeroed debug registers.
+
+ GDB core assumes the child inherits the watchpoints/hw
+ breakpoints of the parent, and will remove them all from the
+ forked off process. Copy the debug registers mirrors into the
+ new process so that all breakpoints and watchpoints can be
+ removed together. The debug registers mirror will become zeroed
+ in the end before detaching the forked off process, thus making
+ this compatible with older Linux kernels too. */
+
+ *child->private->arch_private = *parent->private->arch_private;
+}
+
/* Called when resuming a thread.
If the debug regs have changed, update the thread's copies. */

@@ -3428,6 +3456,7 @@ struct linux_target_ops the_low_target =
x86_siginfo_fixup,
x86_linux_new_process,
x86_linux_new_thread,
+ x86_linux_new_fork,
x86_linux_prepare_to_resume,
x86_linux_process_qsupported,
x86_supports_tracepoints,
--
1.7.0.4