Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

libc, libthr: use AT_USRSTACK{BASE,LIM} instead of sysctl("kern.usrstack") and get_rlimit(RLIMIT_STACK)

Reviewed by: brooks, imp (previous version)
Discussed with: markj
Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks
Differential revision: https://reviews.freebsd.org/D36540

libthr: use nitems() for mib length

Suggested by: imp
Reviewed by: brooks, imp (previous version)
Discussed with: markj
Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks
Differential revision: https://reviews.freebsd.org/D36540

Don't assume objects in program sections have a size of a pointer.

The size of the object at 'addr' is unknown and might be smaller than
the size of a pointer (e.g. some x86 instructions are smaller than a
pointer). Instead, just check that the address is in the bounds of
the program header.

Reported by: CHERI (indirectly)
Reviewed by: kib, brooks
Obtained from: CheriBSD
MFC after: 1 week
Sponsored by: DARPA
Differential Revision: https://reviews.freebsd.org/D26279

Remove redundent decleration of __elf_phdr_match_addr().

Obtained from: CheriBSD
MFC after: 1 week
Sponsored by: DARPA, AFRL

Fix initial exec TLS mode for dynamically loaded shared objects.

If dso uses initial exec TLS mode, rtld tries to allocate TLS in
static space. If there is no space left, the dlopen(3) fails. If space
if allocated, initial content from PT_TLS segment is distributed to
all threads' pcbs, which was missed and caused un-initialized TLS
segment for such dso after dlopen(3).

The mode is auto-detected either due to the relocation used, or if the
DF_STATIC_TLS dynamic flag is set. In the later case, the TLS segment
is tried to allocate earlier, which increases chance of the dlopen(3)
to succeed. LLD was recently fixed to properly emit the flag, ld.bdf
did it always.

Initial test by: dumbbell
Tested by: emaste (amd64), ian (arm)
Tested by: Gerald Aryeetey <aryeeteygerald_rogers.com> (arm64)
Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks
Differential revision: https://reviews.freebsd.org/D19072

Fix PowerPC64 ELFv1-specific problem in __elf_phdr_match_addr() leading to crash
in threaded programs that unload libraries.

Summary:
The GNOME update to 3.28 exposed a bug in __elf_phdr_match_addr(), which leads
to a crash when building devel/libsoup on powerpc64.

Due to __elf_phdr_match_addr() limiting its search to PF_X sections, on the
PPC64 ELFv1 ABI, it was never matching function pointers properly.

This meant that libthr was never cleaning up its atfork list in
__pthread_cxa_finalize(), so if a library with an atfork handler was unloaded,
libthr would crash on the next fork.

Normally, the null pointer check it does before calling the handler would avoid
this crash, but, due to PPC64 ELFv1 using function descriptors instead of raw
function pointers, a null check against the pointer itself is insufficient, as
the pointer itself was not null, it was just pointing at a function descriptor
that had been zeroed. (Which is an ABI violation.)

Calling a zeroed function descriptor on PPC64 ELFv1 causes a jump to address 0
with a zeroed r2 and r11.

Submitted by: git_bdragon.rtk0.net
Reviewed By: kib
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D18364

libc: further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using mis-identified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

If libthr.so is dlopened without RTLD_GLOBAL flag, the libthr symbols
do not participate in the global symbols namespace, but rtld locks are
still replaced and functions are interposed. In particular,
__pthread_map_stacks_exec is resolved to the libc version. If a
library is loaded later, which requires adjustment of the stack
protection mode, rtld calls into libc __pthread_map_stacks_exec due to
the symbols scope. The libc version might recurse into binder and
recursively acquire rtld bind lock, causing the hang.

Make libc __pthread_map_stacks_exec() interposed, which synchronizes
rtld locks and version of the stack exec hook when libthr loaded,
regardless of the symbol scope control or symbol resolution order.

The __pthread_map_stacks_exec() symbol is removed from the private
version in libthr since libc symbol now operates correctly in presence
of libthr.

Reported and tested by: markj
Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks

Remove names from some prototypes

Add declarations to eliminate -Wmissing-prototypes warnings

Implement __pthread_map_stacks_exec() callback for libc, to change the
stack protection to allow execution for single-threaded processes.

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

On shared object unload, in __cxa_finalize, call and clear all installed
atexit and __cxa_atexit handlers that are either installed by unloaded
dso, or points to the functions provided by the dso.

Use _rtld_addr_phdr to locate segment information from the address of
private variable belonging to the dso, supplied by crtstuff.c. Provide
utility function __elf_phdr_match_addr to do the match of address against
dso executable segment.

Call back into libthr from __cxa_finalize using weak
__pthread_cxa_finalize symbol to remove any atfork handler which
function points into unloaded object.

The rtld needs private __pthread_cxa_finalize symbol to not require
resolution of the weak undefined symbol at initialization time. This
cannot work, since rtld is relocated before sym_zero is set up.

Idea by: kan
Reviewed by: kan (previous version)
MFC after: 3 weeks