The debug/pe package assumes there are always 16 entries in
DataDirectory in OptionalHeader32/64
ref pe.go:
...
NumberOfRvaAndSizes uint32
DataDirectory [16]DataDirectory
}
...

But that is not always the case, there could be less no of
entries (PE signed linux kernel for example):
$ sudo pev /boot/vmlinuz-4.15.0-47-generic
....
Data-dictionary entries:	6
....

In such case, the parsing gives incorrect results.
This changes aims to fix that by:
1. Determining type of optional header by looking at header
   magic instead of size
2. Parsing optional header in 2 steps:
   a. Fixed part
   b. Variable data directories part

Testing:
1. Fixed existing test cases to reflect the change
2. Added new file (modified linux kernel image)
   which has smaller number of data directories

Fixes #32126

Change-Id: Iee56ecc4369a0e75a4be805e7cb8555c7d81ae2f
Reviewed-on: https://go-review.googlesource.com/c/go/+/177959
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

pecoff.doc (https://goo.gl/ayvckk) in section 5.6 says:

Immediately following the COFF symbol table is the COFF string table.
The position of this table is found by taking the symbol table address
in the COFF header, and adding the number of symbols multiplied by
the size of a symbol.

So it is unclear what to do when symbol table address is 0.
Lets assume executable does not have any string table.

Added new test with executable with no symbol table. The

gcc -s testdata\hello.c -o testdata\gcc-386-mingw-no-symbols-exec.

command was used to generate the executable.

Fixes #16084

Change-Id: Ie74137ac64b15daadd28e1f0315f3b62d1bf2059
Reviewed-on: https://go-review.googlesource.com/24200
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Preparation was in CL 134570043.
This CL contains only the effect of 'hg mv src/pkg/* src'.
For more about the move, see golang.org/s/go14nopkg.