MFC r281436 (by mjg@):

fd: remove filedesc argument from fdclose

Just accept a thread instead. This makes it consistent with fdalloc.

No functional changes.

MFC 313407,313449: Copy ELF machine/flags from binaries to core dumps.

313407:
Copy the e_machine and e_flags fields from the binary into an ELF core dump.

In the kernel, cache the machine and flags fields from ELF header to use in
the ELF header of a core dump. For gcore, the copy these fields over from
the ELF header in the binary.

This matters for platforms which encode ABI information in the flags field
(such as o32 vs n32 on MIPS).

313449:
Trim trailing whitespace (mostly introduced in r313407).

Sponsored by: DARPA / AFRL

MFC r313992, r314075, r314118, r315484:

r315484:
ptrace_test: eliminate assumption about thread scheduling

A couple of the ptrace tests make assumptions about which thread in a
multithreaded process will run after a halt. This makes the tests less
portable across branches, and susceptible to future breakage. Instead,
twiddle thread scheduling and priorities to match the tests'
expectation.

r314118:
Actually fix buildworlds other than i386/amd64/sparc64 after r313992

Disable offending test for platforms without a userspace visible
breakpoint().

r314075:
Fix world build for archs where __builtin_debugtrap() does not work.

The offending code was introduced in r313992.

r313992:
Defer ptracestop() signals that cannot be delivered immediately

When a thread is stopped in ptracestop(), the ptrace(2) user may request
a signal be delivered upon resumption of the thread. Heretofore, those signals
were discarded unless ptracestop()'s caller was issignal(). Fix this by
modifying ptracestop() to queue up signals requested by the ptrace user that
will be delivered when possible. Take special care when the signal is SIGKILL
(usually generated from a PT_KILL request); no new stop events should be
triggered after a PT_KILL.

Add a number of tests for the new functionality. Several tests were authored
by jhb.

PR: 212607
Sponsored by: Dell EMC

MFC r303426:
Rewrite subr_sleepqueue.c use of callouts to not depend on the
specifics of callout KPI.

MFC r304440, r304487:
Fix some handling of P2_PTRACE_FSTP.

MFC 303001: Add PTRACE_VFORK to trace vfork events.

First, PL_FLAG_FORKED events now also set a PL_FLAG_VFORKED flag when
the new child was created via vfork() rather than fork(). Second, a
new PL_FLAG_VFORK_DONE event can now be enabled via the PTRACE_VFORK
event mask. This new stop is reported after the vfork parent resumes
due to the child calling exit or exec. Debuggers can use this stop to
reinsert breakpoints in the vfork parent process before it resumes.

MFC r303423:
Force SIGSTOP to be the first signal reported after the attach.

MFC 302900,302902,302921,303461,304009:
Add a mask of optional ptrace() events.

302900:
Add a test for user signal delivery.

This test verifies we get the correct ptrace event details when a signal
is posted to a traced process from userland.

302902:
Add a mask of optional ptrace() events.

ptrace() now stores a mask of optional events in p_ptevents. Currently
this mask is a single integer, but it can be expanded into an array of
integers in the future.

Two new ptrace requests can be used to manipulate the event mask:
PT_GET_EVENT_MASK fetches the current event mask and PT_SET_EVENT_MASK
sets the current event mask.

The current set of events include:
- PTRACE_EXEC: trace calls to execve().
- PTRACE_SCE: trace system call entries.
- PTRACE_SCX: trace syscam call exits.
- PTRACE_FORK: trace forks and auto-attach to new child processes.
- PTRACE_LWP: trace LWP events.

The S_PT_SCX and S_PT_SCE events in the procfs p_stops flags have
been replaced by PTRACE_SCE and PTRACE_SCX. PTRACE_FORK replaces
P_FOLLOW_FORK and PTRACE_LWP replaces P2_LWP_EVENTS.

The PT_FOLLOW_FORK and PT_LWP_EVENTS ptrace requests remain for
compatibility but now simply toggle corresponding flags in the
event mask.

While here, document that PT_SYSCALL, PT_TO_SCE, and PT_TO_SCX both
modify the event mask and continue the traced process.

302921:
Rename PTRACE_SYSCALL to LINUX_PTRACE_SYSCALL.

303461:
Note that not all optional ptrace events use SIGTRAP.

New child processes attached due to PTRACE_FORK use SIGSTOP instead of
SIGTRAP. All other ptrace events use SIGTRAP.

304009:
Remove description of P_FOLLOWFORK as this flag was removed.

MFC 292894,292896: Add ptrace(2) reporting for LWP events.

292894:
Add ptrace(2) reporting for LWP events.

Add two new LWPINFO flags: PL_FLAG_BORN and PL_FLAG_EXITED for reporting
thread creation and destruction. Newly created threads will stop to report
PL_FLAG_BORN before returning to userland and exiting threads will stop to
report PL_FLAG_EXIT before exiting completely. Both of these events are
only enabled and reported if PT_LWP_EVENTS is enabled on a process.

292896:
Document the recently added support for ptrace(2) LWP events.

MFC r280331:

cred: add proc_set_cred_init helper

PR: D7431

MFC r280330,r282567:

r280330:
fork: assign refed credentials earlier
r282567:
Fix up panics when fork fails due to hitting proc limit

PR: D7431

MFC r303702:
Remove mention of Giant from the fork_return() description.

MFC r292384:

Fix style issues around existing SDT probes.

** Changes to sys/netinet/in_kdtrace.c and sys/netinet/in_kdtrace.h skipped.

MFC r298819:

sys/kern: spelling fixes in comments.

MFC r280130:

cred: add proc_set_cred helper

MFC r297156,r297157,r297158,r297159,r297161,r297172,r297200,r297201,r297202,
r297203,r297256:

r297156:
Track filemon usage via a proc.p_filemon pointer rather than its own lists.
r297157:
Stop tracking stat(2).
r297158:
Consolidate open(2) and openat(2) code.
r297159:
Use curthread for vn_fullpath.
r297161:
Attempt to use the namecache for openat(2) path resolution.
r297172:
Consolidate common link(2) logic.
r297200:
Follow-up r297156: Close the log in filemon_dtr rather than in the last
reference.
r297201:
Return any log write failure encountered when closing the filemon fd.
r297202:
Remove unused done argument to copyinstr(9).
r297203:
Handle copyin failures.
r297256:
Remove unneeded return left from refactoring.

Relnotes: yes (filemon stability/performance updates)
Sponsored by: EMC / Isilon Storage Division

MFC 295418,295419:
Fix hangs or panics when misbehaved kernel threads return from their
main function.

295418:
Mark proc0 as a kernel process via the P_KTHREAD flag.

All other kernel processes have this flag set and all threads in proc0
(including thread0) have the similar TDP_KTHREAD flag set.

295419:
Call kthread_exit() rather than kproc_exit() for a premature kthread exit.

Kernel threads (and processes) are supposed to call kthread_exit() (or
kproc_exit()) to terminate. However, the kernel includes a fallback in
fork_exit() to force a kthread exit if a kernel thread's "main" routine
returns. This fallback was added back when the kernel only had processes
and was not updated to call kthread_exit() instead of kproc_exit() when
threads were added to the kernel.

This mistake was particularly exciting when the errant thread belonged to
proc0. Due to the missing P_KTHREAD flag the fallback did not kick in
and instead tried to return to userland via whatever garbage was in the
trapframe. With P_KTHREAD set it tried to terminate proc0 resulting in
other amusements.

PR: 204999
Approved by: re (glebius)

MFC r288336: save some bytes by using more concise SDT_PROBE<n>

MFC 287386,288949,288993:
Export current system call code and argument count for system call entry
and exit events. To preserve the ABI, the new fields are moved to the
end of struct thread in these branches (unlike HEAD) and explicitly copied
when new threads are created. In addition, the new tests are only added
in 10.

r287386:
Export current system call code and argument count for system call entry
and exit events. procfs stop events for system call tracing report these
values (argument count for system call entry and code for system call exit),
but ptrace() does not provide this information. (Note that while the system
call code can be determined in an ABI-specific manner during system call
entry, it is not generally available during system call exit.)

The values are exported via new fields at the end of struct ptrace_lwpinfo
available via PT_LWPINFO.

r288949:
Fix various edge cases related to system call tracing.
- Always set td_dbg_sc_* when P_TRACED is set on system call entry
even if the debugger is not tracing system call entries. This
ensures the fields are valid when reporting other stops that
occur at system call boundaries such as for PT_FOLLOW_FORKS or
when only tracing system call exits.
- Set TDB_SCX when reporting the stop for a new child process in
fork_return(). This causes the event to be reported as a system
call exit.
- Report a system call exit event in fork_return() for new threads in
a traced process.
- Copy td_dbg_sc_* to new threads instead of zeroing. This ensures
that td_dbg_sc_code in particular will report the system call that
created the new thread or process when it reports a system call
exit event in fork_return().
- Add new ptrace tests to verify that new child processes and threads
report system call exit events with a valid pl_syscall_code via
PT_LWPINFO.

r288993:
Document the recently added pl_syscall_* fields in struct ptrace_lwpinfo.

MFC r289026:
Enforce the maxproc limitation before allocating struct proc.

In collaboration with: pho

MFC 283546:
Add KTR tracing for some MI ptrace events.

Add chunk missed in the r284199.

MFC r277322:
Add procctl(2) PROC_TRACE_CTL command to enable or disable debugger
attachment to the process.

Merge reaper facility.

MFC r270443 (by mjg):
Properly reparent traced processes when the tracer dies.

MFC r273452 (by mjg):
Plug unnecessary PRS_NEW check in kern_procctl.

MFC 275800:
Add a facility for non-init process to declare itself the reaper of
the orphaned descendants.

MFC r275821:
Add missed break.

MFC r275846 (by mckusick):
Add some additional clarification and fix a few gammer nits.

MFC r275847 (by bdrewery):
Bump Dd for r275846.

MFC r275745:
Add facility to stop all userspace processes.

MFC r275753:
Fix gcc build.

MFC r275820:
Add missed break.

Commit forgotten chunk of r270264.

MFC r268001:
Make fdunshare accept only td parameter.

Proc had to match the thread anyway and 2 parameters were inconsistent
with the rest.

MFC r259535:
The fasttrap fork handler is responsible for removing tracepoints in the
child process that were inherited from its parent. However, this should
not be done in the case of a vfork, since the fork handler ends up removing
the tracepoints from the shared vm space, and userland DTrace probes in the
parent will no longer fire as a result.

Now the child of a vfork may trigger userland DTrace probes enabled in its
parent, so modify the fasttrap probe handler to handle this case and handle
the child process in the same way that it would handle the traced process.
In particular, if once traces function foo() in a process that vforks, and
the child calls foo(), fasttrap will treat this call as having come from the
parent. This is the behaviour of the upstream code.

While here, add #ifdef guards to some code that isn't present upstream.

MFC r258622: dtrace sdt: remove the ugly sname parameter of SDT_PROBE_DEFINE

MFC 283546:
Add KTR tracing for some MI ptrace events.

Add chunk missed in the r284199.

MFC r277322:
Add procctl(2) PROC_TRACE_CTL command to enable or disable debugger
attachment to the process.

Merge reaper facility.

MFC r270443 (by mjg):
Properly reparent traced processes when the tracer dies.

MFC r273452 (by mjg):
Plug unnecessary PRS_NEW check in kern_procctl.

MFC 275800:
Add a facility for non-init process to declare itself the reaper of
the orphaned descendants.

MFC r275821:
Add missed break.

MFC r275846 (by mckusick):
Add some additional clarification and fix a few gammer nits.

MFC r275847 (by bdrewery):
Bump Dd for r275846.

MFC r275745:
Add facility to stop all userspace processes.

MFC r275753:
Fix gcc build.

MFC r275820:
Add missed break.

Commit forgotten chunk of r270264.

MFC r268001:
Make fdunshare accept only td parameter.

Proc had to match the thread anyway and 2 parameters were inconsistent
with the rest.

MFC r259535:
The fasttrap fork handler is responsible for removing tracepoints in the
child process that were inherited from its parent. However, this should
not be done in the case of a vfork, since the fork handler ends up removing
the tracepoints from the shared vm space, and userland DTrace probes in the
parent will no longer fire as a result.

Now the child of a vfork may trigger userland DTrace probes enabled in its
parent, so modify the fasttrap probe handler to handle this case and handle
the child process in the same way that it would handle the traced process.
In particular, if once traces function foo() in a process that vforks, and
the child calls foo(), fasttrap will treat this call as having come from the
parent. This is the behaviour of the upstream code.

While here, add #ifdef guards to some code that isn't present upstream.

MFC r258622: dtrace sdt: remove the ugly sname parameter of SDT_PROBE_DEFINE