MFC r328052: kldxref: handle modules with md_cval at end of allocated secs

Attempting to retrieve an md_cval string from a kernel module with
kldxref would throw a offset error for modules created using lld, since
this value would be placed at the end of all allocated sections.

Add an ef_read_seg_string method to the ef interface, to allow reading
strings of varying size without attempting to read beyond the segment's
bounds.

PR: 224875
Submitted by: Mitchell Horne <mhorne063@gmail.com>
Sponsored by: The FreeBSD Foundation

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Make our ELF64 type definitions match standards. In particular this
means:
o Remove Elf64_Quarter,
o Redefine Elf64_Half to be 16-bit,
o Redefine Elf64_Word to be 32-bit,
o Add Elf64_Xword and Elf64_Sxword for 64-bit entities,
o Use Elf_Size in MI code to abstract the difference between
Elf32_Word and Elf64_Word.
o Add Elf_Ssize as the signed counterpart of Elf_Size.

MFC after: 2 weeks

Explicitly pass in the relocation base and data offset into ef_reloc()
rather than relying on a trick that happens to work for the current
relocation schemes. Also add some comments and improve variable
naming.

Call the file format specific code through a table of function
pointers and remove knowledge of the file format from kldxref.c.
This will make it possible to support more than one file format.

Fix kldxref on sparc64 by allowing non-trivial relocations to be performed
on variables read out of raw kld files. Unlike other platforms the value
will be in an Elf_Rela, not in the data section of the elf file.

Submitted by: Hartmut Brandt <brandt@fokus.gmd.de>
PR: 46730
Tested on: alpha (obrien), i386, sparc64

Make kldxref work for Elf64 (which has 32 bit hash tables)

Add kldxref(8), for maintaining the linker.hints file for translating
module->pathname.ko. It supports only ELF for now.

Submitted by: bp (with some minor tweaks)