rtld snprintf: do not erronously skip a char at the buffer boundary

Reviewed by: emaste, markj
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D44987

Remove $FreeBSD$: two-line .h pattern

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

rtld: add rtld_fdprintfx()

It is same as rtld_fdprintf() without enforcement of the format string
to be a literal.

Sponsored by: The FreeBSD Foundation
MFC after: 1 week

Reduce size of rtld by 22% by pulling in less code from libc

Currently RTLD is linked against libc_nossp_pic which means that any libc
symbol used in rtld can pull in a lot of depedencies. This was causing
symbol such as __libc_interposing and all the pthread stubs to be included
in RTLD even though they are not required. It turns out most of these
dependencies can easily be avoided by providing overrides inside of rtld.

This change is motivated by CHERI, where we have an experimental ABI that
requires additional relocation processing to allow the use of function
pointers inside of rtld. Instead of adding this self-relocation code to
RTLD I attempted to remove most function pointers from RTLD and discovered
that most of them came from the libc dependencies instead of being actually
used inside rtld.

A nice side-effect of this change is that rtld is now 22% smaller on amd64.

text data bss dec hex filename
0x21eb6 0xce0 0xe60 145910 239f6 /home/alr48/ld-elf-x86.before.so.1
0x1a6ed 0x728 0xdd8 113645 1bbed /home/alr48/ld-elf-x86.after.so.1

The number of R_X86_64_RELATIVE relocations that need to be processed on
startup has also gone down from 368 to 187 (almost 50% less).

Reviewed By: kib
Differential Revision: https://reviews.freebsd.org/D20663

rtld-elf: fix more warnings to allow compiling with WARNS=6

Reviewed By: kib
Approved By: brooks (mentor)
Differential Revision: https://reviews.freebsd.org/D17154

General further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 3-Clause license.

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.

Special thanks to Wind River for providing access to "The Duke of
Highlander" tool: an older (2014) run over FreeBSD tree was useful as a
starting point.

Renumber copyright clause 4

Renumber cluase 4 to 3, per what everybody else did when BSD granted
them permission to remove clause 3. My insistance on keeping the same
numbering for legal reasons is too pedantic, so give up on that point.

Submitted by: Jan Schaumann <jschauma@stevens.edu>
Pull Request: https://github.com/freebsd/freebsd/pull/96

Add the LD_LIBRARY_PATH_FDS environmental variable.

This variable allows the loading of shared libraries via directory descriptors
rather than via library paths. If LD_LIBRARY_PATH_FDS=3:4:12, the directories
represented by file descriptors 3, 4 and 12 will searched for shared libraries
before the normal path-based mechanisms are used. This allows us to execute
unprivileged binaries from within a Capsicum sandbox even if they require
shared libraries.

Approved by: rwatson (mentor)
Reviewed by: kib
MFC after: 3 weeks
Sponsored by: DARPA/AFRL

Remove the use of toupper() from rtld_printf.c. Use of the libc function
relies on working TLS, which is particulary not true for LD_DEBUG uses.

MFC after: 1 week

Do not use the function pointers for the internal operation of rtld_printf()
functions. The _rtld_error() function might be called early during the rtld
bootstrap, in which case function pointers are not yet functional on ia64
due to required relocations not yet performed.

Reported, reviewed and tested by: marcel
Approved by: re (bz)

Rtld links with the specially built pic static libc library to get some
C runtime services, like printf(). Unfortunately, the multithread-safeness
measures in the libc do not work in rtld environment.

Rip the kernel printf() implementation and use it in the rtld instead of
libc version. This printf does not require any shared global data and thus
is mt-safe. Systematically use rtld_printf() and related functions, remove
the calls to err(3).

Note that stdio is still pulled from libc due to libmap implementaion using
fopen(). This is safe but unoptimal, and can be changed later.

Reported and tested by: pgj
Diagnosed and reviewed by: kan (previous version)
Approved by: re (bz)