[metadata]
id = "CON32-C"
type = "recommendation"
category = "CON"
number = 32
title = "Prevent data races when accessing bit-fields from multiple threads"
description = """
When accessing a bit-field, a thread may inadvertently access a separate bit-
field in adjacent memory. This is because compilers are required to store
multiple adjacent bit-fields in one storage unit whenever they fit.
Consequently, data races may exist not just on a bit-field accessed by multiple
threads but also on other bit-fields sharing the same byte or word. A similar
problem is discussed inCON43-C. Do not allow data races in multithreaded code,
but the issue described by this rule can be harder to diagnose because it may
not be obvious that the same memory location is being modified by multiple
threads. One approach for preventing data races in concurrent programming is to
use a mutex. When properly observed by all threads, a mutex can provide safe and
secure access to a shared object. However, mutexes provide no guarantees with
regard to other objects that might be accessed when the mutex is not controlled
by the accessing thread. Unfortunately, there is no portable way to determine
which adjacent bit-fields may be stored along with the desired bit-field.
Another approach is to insert a non-bit-field member between any two bit-fields
to ensure that each bit-field is the only one accessed within its storage unit.
This technique effectively guarantees that no two bit-fields are accessed
simultaneously.
"""
severity = "Medium"
likelihood = "Probable"
priority = "P4"
level = "L3"
cert_version = "2016 Edition (Wiki)"
last_modified = "May 06, 2025"
[rules.cert_c.CON32-C]
enabled = true
[references]
wiki = "https://wiki.sei.cmu.edu/confluence/display/c/CON32-C.+Prevent+data+races+when+accessing+bit-fields+from+multiple+threads"