modpost: work around unaligned data access error

With the latest binutils, modpost fails with a bus error on some
architectures such as ARM and sparc64.

Since binutils commit 1f1b5e506bf0 ("bfd/ELF: restrict file alignment
for object files"), the byte offset to each section (sh_offset) in
relocatable ELF is no longer guaranteed to be aligned.

modpost parses MODULE_DEVICE_TABLE() data structures, which are usually
located in the .rodata section. If it is not properly aligned, unaligned
access errors may occur.

To address the issue, this commit imports the get_unaligned() helper
from include/linux/unaligned.h.

The get_unaligned_native() helper caters to the endianness in addition
to handling the unaligned access.

I slightly refactored do_pcmcia_entry() and do_input() to avoid writing
back to an unaligned address. (We would need the put_unaligned() helper
to do that.)

The addend_*_rel() functions need similar adjustments because the .text
sections are not aligned either.

It seems that the .symtab, .rel.* and .rela.* sections are still aligned.
Keep normal pointer access for these sections to avoid unnecessary
performance costs.

Reported-by: Paulo Pisati <[email protected]>
Reported-by: Matthias Klose <[email protected]>
Closes: https://sourceware.org/bugzilla/show_bug.cgi?id=32435
Reported-by: John Paul Adrian Glaubitz <[email protected]>
Closes: https://sourceware.org/bugzilla/show_bug.cgi?id=32493
Signed-off-by: Masahiro Yamada <[email protected]>
Tested-by: John Paul Adrian Glaubitz <[email protected]>

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