MFC r366085, r366113:
Do not leak oldvmspace if image activation failed

MFC r354789:
kern_exec: p_osrel and p_fctl0 were obliterated by failed execve(2) attempt.

MFC 350549: Set ISOPEN in namei flags when opening executable interpreters.

These vnodes are explicitly opened via VOP_OPEN via
exec_check_permissions identical to the main exectuable image.
Setting ISOPEN allows filesystems to perform suitable checks in
VOP_LOOKUP (e.g. close-to-open consistency in the NFS client).

MFC r351773:
Add procctl(PROC_STACKGAP_CTL).

PR: 239894

MFC r337965:
capsicum: allow the setproctitle(3) function in capability mode

Capsicum in past allowed to change the process title.
This was broken with r335939.

PR: 230584
Submitted by: Yuichiro NAITO <naito.yuichiro@gmail.com>
Reported by: ian@niw.com.au
MFC after: 1 week

MFC 332782:
Simplify the code to allocate stack for auxv, argv[], and environment vectors.

Remove auxarg_size as it was only used once right after a confusing
assignment in each of the variants of exec_copyout_strings().

MFC r336238:

Round down the location of execpathp to slightly improve copyout speed.

In practice, this moves the padding from below the canary to above
execpathp has no impact on stack consumption.

Submitted by: Wuyang-Chung (via github pull request #159)

MFC r332740:
Add PROC_PDEATHSIG_SET to procctl interface.

MFC r332825:
Rename PROC_PDEATHSIG_SET -> PROC_PDEATHSIG_CTL.

MFC r333067:
Remove redundant pipe from pdeathsig.c test.

MFC r325621, r325622, r331227

Add EVENTHANDLER_LIST and some users.

Also fix a longstanding bug in mtx initialization.

MFC r314568 (by emaste):

kern_sig.c: ANSIfy and remove archaic register keyword

Sponsored by: The FreeBSD Foundation

MFC r318389 (by emaste):

Remove register keyword from sys/ and ANSIfy prototypes

A long long time ago the register keyword told the compiler to store
the corresponding variable in a CPU register, but it is not relevant
for any compiler used in the FreeBSD world today.

ANSIfy related prototypes while here.

Reviewed by: cem, jhb
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D10193

MFC r328996: exec_map_first_page: fix an inverse condition introduced in r254138

MFC r320498
Clear the MAP_WIREFUTURE flag on the vm map in exec_new_vmspace() when it
recycles the current vm space. Otherwise, an mlockall(MCL_FUTURE) could
still be in effect on the process after an execve(2), which violates the
specification for mlockall(2).

It's pointless for vm_map_stack() to check the MEMLOCK limit. It will
never be asked to wire the stack. Moreover, it doesn't even implement
wiring of the stack.

MFC r320619:
Resolve confusion between different error code spaces.

Direct commit to fix a mismerge in r320797.

MFC r311346, r311352, r313756:
Add an allocator for KVA for execve arguments.

MFC r308474, r308691, r309203, r309365, r309703, r309898, r310720,
r308489, r308706:
Add PQ_LAUNDRY and remove PG_CACHED pages.

MFC r307653:

Mark a bunch of mpsafe sysctls as such.

This gives me a sysctl Giant-free buildworld.

MFC r304102
Eliminate unneeded vm_page_xbusy() and vm_page_xunbusy() operations when
neither vm_pager_has_page() nor vm_pager_get_pages() is called.

MFC r304050
Eliminate two calls to vm_page_xunbusy() that are both unnecessary and
incorrect from the error cases in exec_map_first_page(). They are
unnecessary because we automatically unbusy the page in vm_page_free()
when we remove it from the object. The calls are incorrect because they
happen after the page is freed, so we might actually unbusy the page
after it has been reallocated to a different object. (This error was
introduced in r292373.)

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 r302614:
Revive the check, disabled in r197963.

MFC r302999:
On first exec after vfork(), call signotify() to handle pending
reenabled signals.

Approved by: re (delphij)