misc: updated shabang for python script

The default python on MacOS doesn’t have an alias to python2.
The official python version supported in gem5 is Python2.7.

This patch updates the shabang according to the version required in gem5.

Change-Id: I9533c0f7858b5b3cab0ef101be1ee5cd718105b0
Reviewed-on: https://gem5-review.googlesource.com/c/15375
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>

misc: Update #!env calls for python to explicit version

In some newer Linux distributions, env python default to Python 3.0. This
patch explicitly uses "python2" instead of just "python" for all scripts
that use #!

Reported-by: Sanchayan Maity <maitysanchayan@gmail.com>
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>

util: git pre-commit hook to check staged files

This patch updates the git-pre-commit hook to check the files as they
will be after the commit, instead of as they are currently, this way we
prevent the undesired situation:
- unstylish modification of a file
- stage said file for commit
- try to commit and fail due to style
- fix style, forgetting staging changes
- try to commit and fail, as although the changes staged are not
styly, the current content of the file is.

Change-Id: I5cc3f783375d9e4162e310e176103ebbf0a59023
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
[andreas.sandberg@arm.com: Rebased ontop of latest gem5]

style: Make the style fixers safe

Adds a wrapper to the fix functions of the verifiers. This wrapper first
copies the original file to a backup file, then performs the fix. If an
error occurs, the backup file is used to restore the original file.

Also fixed a line-length error in verifiers.py

style: Fix incorrect references style verifiers

The style checker for spacing around control statements (ControlSpace)
and the whitespace checker (Whitespace) didn't refer to some of their
configuration variables correctly. This changeset fixes those issues.

Reported-by: Jason Lowe-Power <power.jg@gmail.com>

style: catch trailing white spaces in make and dts files

Change-Id: I2a4f1893919660e51599902b972a6f3f5717e305
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>

style: remove extra newline from white space verifier fix method

Change-Id: I7bce7d1cb04efe20d31445eb67ea5ffd2a4a41f4
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>

style: Fix Python 2.6 compatibility

The style checker code needs to disable autojunk when diffing source
files using Python's difflib. Support for this was only introduced in
Python 2.7, which leads to a TypeError exception on older Python
version. This changeset adds a fallback mechanism for old Python
versions.

style: Change maximum line length to 79 characters

The old style guide used to mandate 78 characters as the maximum line
length to accommodate traditional diffs on 80-column terminals. This
is an uncommon use case and it has therefore been decided (see email
thread on gem5-dev [1]) that a maximum length of 79-characters makes
more sense.

[1] http://comments.gmane.org/gmane.comp.emulators.m5.devel/29789

Signed-off-by: Andreas Sandberg <aandreas.sandberg@arm.com>
Reviewed-by: Brandon Potter <brandon.potter@amd.com>

style: Add a control character checker

Add a style checker that verifies that source code doesn't contain
non-printable (control) characters. The only allowed control
characters are:

* 0x0a / \n: New line
* 0x09 / \t: Tab (the whitespace checker enforces no-tabs for C/C++ files)

Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Brandon Potter <brandon.potter@amd.com>

style: Refactor the style checker as a Python package

Refactor the style checker into a Python module that can be reused by
command line tools that integrate with git. In particular:

* Create a style package in util
* Move style validators from style.py to the style/validators.py.
* Move style verifiers from style.py to the style/verifiers.py.
* Move utility functions (sort_includes, region handling,
file_types) into the style package
* Move generic code from style.py to style/style.py.

Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-by: Steve Reinhardt <steve.reinhardt@amd.com>