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Revision 3dbae15538972c9e1578cb216964c2840361a538 authored by Gustavo A. R. Silva on 15 February 2020, 01:03:12 UTC, committed by Dmitry Torokhov on 15 February 2020, 01:19:22 UTC 
Input: cyapa - replace zero-length array with flexible-array member
 
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Link: https://lore.kernel.org/r/20200214172132.GA28389@embeddedor
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
1 parent 94bef5d
Raw File
jobserver-exec 
#!/usr/bin/env python
# SPDX-License-Identifier: GPL-2.0+
#
# This determines how many parallel tasks "make" is expecting, as it is
# not exposed via an special variables, reserves them all, runs a subprocess
# with PARALLELISM environment variable set, and releases the jobs back again.
#
# https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserver
from __future__ import print_function
import os, sys, errno
import subprocess

# Extract and prepare jobserver file descriptors from envirnoment.
claim = 0
jobs = b""
try:
	# Fetch the make environment options.
	flags = os.environ['MAKEFLAGS']

	# Look for "--jobserver=R,W"
	# Note that GNU Make has used --jobserver-fds and --jobserver-auth
	# so this handles all of them.
	opts = [x for x in flags.split(" ") if x.startswith("--jobserver")]

	# Parse out R,W file descriptor numbers and set them nonblocking.
	fds = opts[0].split("=", 1)[1]
	reader, writer = [int(x) for x in fds.split(",", 1)]
	# Open a private copy of reader to avoid setting nonblocking
	# on an unexpecting process with the same reader fd.
	reader = os.open("/proc/self/fd/%d" % (reader),
			 os.O_RDONLY | os.O_NONBLOCK)

	# Read out as many jobserver slots as possible.
	while True:
		try:
			slot = os.read(reader, 8)
			jobs += slot
		except (OSError, IOError) as e:
			if e.errno == errno.EWOULDBLOCK:
				# Stop at the end of the jobserver queue.
				break
			# If something went wrong, give back the jobs.
			if len(jobs):
				os.write(writer, jobs)
			raise e
	# Add a bump for our caller's reserveration, since we're just going
	# to sit here blocked on our child.
	claim = len(jobs) + 1
except (KeyError, IndexError, ValueError, OSError, IOError) as e:
	# Any missing environment strings or bad fds should result in just
	# not being parallel.
	pass

# We can only claim parallelism if there was a jobserver (i.e. a top-level
# "-jN" argument) and there were no other failures. Otherwise leave out the
# environment variable and let the child figure out what is best.
if claim > 0:
	os.environ['PARALLELISM'] = '%d' % (claim)

rc = subprocess.call(sys.argv[1:])

# Return all the reserved slots.
if len(jobs):
	os.write(writer, jobs)

sys.exit(rc)
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