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Enable fork tracing for native FreeBSD targets.

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Enable PT_FOLLOW_FORK on all processes.  When this is enabled, both
the parent and child process stop when a fork or vfork occurs.

A target operation for wait uses PT_LWPINFO to fetch more detailed
information about the state of a stopped process.  A parent process
sets the PL_FLAG_FORKED flag in the pl_flags field of the structure
returned by PT_LWPINFO as well as the pid of the new child process.
The child process sets the PL_FLAG_CHILD flag in the pl_flags field.

When a fork is detected, the wait hook waits for both processes to
report their respective events.  It then reports the fork to GDB as
a single TARGET_WAITKIND_FORKED or TARGET_WAITKIND_VFORKED event.
The kernel does not guarantee the order the events are reported in.
If the parent process' event is reported first, then the wait hook
explicitly waits for the child process.  If the child process' event
is reported first, the event is recorded on an internal list of
pending child events and the wait hook waits for another event.
Later when the parent process' event is reported, the parent will
use the previously-recorded child process event instead of explicitly
waiting on the child process.

To distinguish vfork events from fork events, the external process
structure for the child process is extracted from the kernel.  The
P_PPWAIT flag is set in the ki_flags field of this structure if the
process was created via vfork, but it is not set for a regular fork.

gdb/ChangeLog:

	* fbsd-nat.c: [PT_LWPINFO] New variable super_wait.
	[TDP_RFPPWAIT] New variable fbsd_pending_children.
	[TDP_RFPPWAIT] (fbsd_remember_child): New function.
	[TDP_RFPPWAIT] (fbsd_is_child_pending): New function.
	[TDP_RFPPWAIT] (fbsd_fetch_kinfo_proc): New function.
	[PT_LWPINFO] (fbsd_wait): New function.
	[TDP_RFPPWAIT] (fbsd_follow_fork): New function.
	[TDP_RFPPWAIT] (fbsd_insert_fork_catchpoint): New function.
	[TDP_RFPPWAIT] (fbsd_remove_fork_catchpoint): New function.
	[TDP_RFPPWAIT] (fbsd_insert_vfork_catchpoint): New function.
	[TDP_RFPPWAIT] (fbsd_remove_vfork_catchpoint): New function.
	[TDP_RFPPWAIT] (fbsd_enable_follow_fork): New function.
	[TDP_RFPPWAIT] (fbsd_post_startup_inferior): New function.
	[TDP_RFPPWAIT] (fbsd_post_attach): New function.
	(fbsd_nat_add_target) [PT_LWPINFO] Set "to_wait" to
	"fbsd_wait".
	[TDP_RFPPWAIT] Set "to_follow_fork" to "fbsd_follow_fork".
	Set "to_insert_fork_catchpoint" to "fbsd_insert_fork_catchpoint".
	Set "to_remove_fork_catchpoint" to "fbsd_remove_fork_catchpoint".
	Set "to_insert_vfork_catchpoint" to "fbsd_insert_vfork_catchpoint".
	Set "to_remove_vfork_catchpoint" to "fbsd_remove_vfork_catchpoint".
	Set "to_post_startup_inferior" to "fbsd_post_startup_inferior".
	Set "to_post_attach" to "fbsd_post_attach".
This commit is contained in:
John Baldwin 2015-04-17 16:20:47 -04:00
parent 8f60fe014d
commit e58e05d677
2 changed files with 298 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

26
gdb/ChangeLog
View file

@ -1,3 +1,29 @@
2015-04-27 John Baldwin <jhb@FreeBSD.org>
* fbsd-nat.c: [PT_LWPINFO] New variable super_wait.
[TDP_RFPPWAIT] New variable fbsd_pending_children.
[TDP_RFPPWAIT] (fbsd_remember_child): New function.
[TDP_RFPPWAIT] (fbsd_is_child_pending): New function.
[TDP_RFPPWAIT] (fbsd_fetch_kinfo_proc): New function.
[PT_LWPINFO] (fbsd_wait): New function.
[TDP_RFPPWAIT] (fbsd_follow_fork): New function.
[TDP_RFPPWAIT] (fbsd_insert_fork_catchpoint): New function.
[TDP_RFPPWAIT] (fbsd_remove_fork_catchpoint): New function.
[TDP_RFPPWAIT] (fbsd_insert_vfork_catchpoint): New function.
[TDP_RFPPWAIT] (fbsd_remove_vfork_catchpoint): New function.
[TDP_RFPPWAIT] (fbsd_enable_follow_fork): New function.
[TDP_RFPPWAIT] (fbsd_post_startup_inferior): New function.
[TDP_RFPPWAIT] (fbsd_post_attach): New function.
(fbsd_nat_add_target) [PT_LWPINFO] Set "to_wait" to
"fbsd_wait".
[TDP_RFPPWAIT] Set "to_follow_fork" to "fbsd_follow_fork".
Set "to_insert_fork_catchpoint" to "fbsd_insert_fork_catchpoint".
Set "to_remove_fork_catchpoint" to "fbsd_remove_fork_catchpoint".
Set "to_insert_vfork_catchpoint" to "fbsd_insert_vfork_catchpoint".
Set "to_remove_vfork_catchpoint" to "fbsd_remove_vfork_catchpoint".
Set "to_post_startup_inferior" to "fbsd_post_startup_inferior".
Set "to_post_attach" to "fbsd_post_attach".
2015-04-27 John Baldwin <jhb@FreeBSD.org>
* fbsd-nat.c (fbsd_pid_to_exec_file): Mark static.

272
gdb/fbsd-nat.c
View file

@ -25,7 +25,9 @@
#include "gdbthread.h"
#include <sys/types.h>
#include <sys/procfs.h>
#include <sys/ptrace.h>
#include <sys/sysctl.h>
#include <sys/wait.h>
#ifdef HAVE_KINFO_GETVMMAP
#include <sys/user.h>
#include <libutil.h>
@ -201,10 +203,280 @@ fbsd_find_memory_regions (struct target_ops *self,
}
#endif
#ifdef PT_LWPINFO
static ptid_t (*super_wait) (struct target_ops *,
ptid_t,
struct target_waitstatus *,
int);
#ifdef TDP_RFPPWAIT
/*
To catch fork events, PT_FOLLOW_FORK is set on every traced process
to enable stops on returns from fork or vfork. Note that both the
parent and child will always stop, even if system call stops are not
enabled.
After a fork, both the child and parent process will stop and report
an event. However, there is no guarantee of order. If the parent
reports its stop first, then fbsd_wait explicitly waits for the new
child before returning. If the child reports its stop first, then
the event is saved on a list and ignored until the parent's stop is
reported. fbsd_wait could have been changed to fetch the parent PID
of the new child and used that to wait for the parent explicitly.
However, if two threads in the parent fork at the same time, then
the wait on the parent might return the "wrong" fork event.
The initial version of PT_FOLLOW_FORK did not set PL_FLAG_CHILD for
the new child process. This flag could be inferred by treating any
events for an unknown pid as a new child.
In addition, the initial version of PT_FOLLOW_FORK did not report a
stop event for the parent process of a vfork until after the child
process executed a new program or exited. The kernel was changed to
defer the wait for exit or exec of the child until after posting the
stop event shortly after the change to introduce PL_FLAG_CHILD.
This could be worked around by reporting a vfork event when the
child event posted and ignoring the subsequent event from the
parent.
This implementation requires both of these fixes for simplicity's
sake. FreeBSD versions newer than 9.1 contain both fixes.
*/
struct fbsd_fork_child_info
{
struct fbsd_fork_child_info *next;
pid_t child; /* Pid of new child. */
};
static struct fbsd_fork_child_info *fbsd_pending_children;
/* Record a new child process event that is reported before the
corresponding fork event in the parent. */
static void
fbsd_remember_child (pid_t pid)
{
struct fbsd_fork_child_info *info;
info = xcalloc (1, sizeof *info);
info->child = pid;
info->next = fbsd_pending_children;
fbsd_pending_children = info;
}
/* Check for a previously-recorded new child process event for PID.
If one is found, remove it from the list. */
static int
fbsd_is_child_pending (pid_t pid)
{
struct fbsd_fork_child_info *info, *prev;
prev = NULL;
for (info = fbsd_pending_children; info; prev = info, info = info->next)
{
if (info->child == pid)
{
if (prev == NULL)
fbsd_pending_children = info->next;
else
prev->next = info->next;
xfree (info);
return 1;
}
}
return 0;
}
/* Fetch the external variant of the kernel's internal process
structure for the process PID into KP. */
static void
fbsd_fetch_kinfo_proc (pid_t pid, struct kinfo_proc *kp)
{
size_t len;
int mib[4];
len = sizeof *kp;
mib[0] = CTL_KERN;
mib[1] = KERN_PROC;
mib[2] = KERN_PROC_PID;
mib[3] = pid;
if (sysctl (mib, 4, kp, &len, NULL, 0) == -1)
perror_with_name (("sysctl"));
}
#endif
/* Wait for the child specified by PTID to do something. Return the
process ID of the child, or MINUS_ONE_PTID in case of error; store
the status in *OURSTATUS. */
static ptid_t
fbsd_wait (struct target_ops *ops,
ptid_t ptid, struct target_waitstatus *ourstatus,
int target_options)
{
ptid_t wptid;
while (1)
{
wptid = super_wait (ops, ptid, ourstatus, target_options);
if (ourstatus->kind == TARGET_WAITKIND_STOPPED)
{
struct ptrace_lwpinfo pl;
pid_t pid;
int status;
pid = ptid_get_pid (wptid);
if (ptrace (PT_LWPINFO, pid, (caddr_t)&pl, sizeof pl) == -1)
perror_with_name (("ptrace"));
#ifdef TDP_RFPPWAIT
if (pl.pl_flags & PL_FLAG_FORKED)
{
struct kinfo_proc kp;
pid_t child;
child = pl.pl_child_pid;
ourstatus->kind = TARGET_WAITKIND_FORKED;
ourstatus->value.related_pid = pid_to_ptid (child);
/* Make sure the other end of the fork is stopped too. */
if (!fbsd_is_child_pending (child))
{
pid = waitpid (child, &status, 0);
if (pid == -1)
perror_with_name (("waitpid"));
gdb_assert (pid == child);
if (ptrace (PT_LWPINFO, child, (caddr_t)&pl, sizeof pl) == -1)
perror_with_name (("ptrace"));
gdb_assert (pl.pl_flags & PL_FLAG_CHILD);
}
/* For vfork, the child process will have the P_PPWAIT
flag set. */
fbsd_fetch_kinfo_proc (child, &kp);
if (kp.ki_flag & P_PPWAIT)
ourstatus->kind = TARGET_WAITKIND_VFORKED;
return wptid;
}
if (pl.pl_flags & PL_FLAG_CHILD)
{
/* Remember that this child forked, but do not report it
until the parent reports its corresponding fork
event. */
fbsd_remember_child (ptid_get_pid (wptid));
continue;
}
#endif
}
return wptid;
}
}
#ifdef TDP_RFPPWAIT
/* Target hook for follow_fork. On entry and at return inferior_ptid is
the ptid of the followed inferior. */
static int
fbsd_follow_fork (struct target_ops *ops, int follow_child,
int detach_fork)
{
if (!follow_child)
{
struct thread_info *tp = inferior_thread ();
pid_t child_pid = ptid_get_pid (tp->pending_follow.value.related_pid);
/* Breakpoints have already been detached from the child by
infrun.c. */
if (ptrace (PT_DETACH, child_pid, (PTRACE_TYPE_ARG3)1, 0) == -1)
perror_with_name (("ptrace"));
}
return 0;
}
static int
fbsd_insert_fork_catchpoint (struct target_ops *self, int pid)
{
return 0;
}
static int
fbsd_remove_fork_catchpoint (struct target_ops *self, int pid)
{
return 0;
}
static int
fbsd_insert_vfork_catchpoint (struct target_ops *self, int pid)
{
return 0;
}
static int
fbsd_remove_vfork_catchpoint (struct target_ops *self, int pid)
{
return 0;
}
/* Enable fork tracing for a specific process.
To catch fork events, PT_FOLLOW_FORK is set on every traced process
to enable stops on returns from fork or vfork. Note that both the
parent and child will always stop, even if system call stops are
not enabled. */
static void
fbsd_enable_follow_fork (pid_t pid)
{
if (ptrace (PT_FOLLOW_FORK, pid, (PTRACE_TYPE_ARG3)0, 1) == -1)
perror_with_name (("ptrace"));
}
/* Implement the "to_post_startup_inferior" target_ops method. */
static void
fbsd_post_startup_inferior (struct target_ops *self, ptid_t pid)
{
fbsd_enable_follow_fork (ptid_get_pid (pid));
}
/* Implement the "to_post_attach" target_ops method. */
static void
fbsd_post_attach (struct target_ops *self, int pid)
{
fbsd_enable_follow_fork (pid);
}
#endif
#endif
void
fbsd_nat_add_target (struct target_ops *t)
{
t->to_pid_to_exec_file = fbsd_pid_to_exec_file;
t->to_find_memory_regions = fbsd_find_memory_regions;
#ifdef PT_LWPINFO
super_wait = t->to_wait;
t->to_wait = fbsd_wait;
#ifdef TDP_RFPPWAIT
t->to_follow_fork = fbsd_follow_fork;
t->to_insert_fork_catchpoint = fbsd_insert_fork_catchpoint;
t->to_remove_fork_catchpoint = fbsd_remove_fork_catchpoint;
t->to_insert_vfork_catchpoint = fbsd_insert_vfork_catchpoint;
t->to_remove_vfork_catchpoint = fbsd_remove_vfork_catchpoint;
t->to_post_startup_inferior = fbsd_post_startup_inferior;
t->to_post_attach = fbsd_post_attach;
#endif
#endif
add_target (t);
}