6.7.7.50 Trivial-auto-var-init Option
The -ftrivial-auto-var-init=choice option instructs the
compiler to initialize automatic variables that have not been explicitly initialized in
the source code with either a pattern or with zeroes. Doing so can increase the security
and predictability of a program by preventing uninitialized memory disclosure and use.
Even with this feature in effect, automatic variables that do not have an explicit
initializer are treated as uninitialized. The -Wuninitialized and
-Wanalyzer-use-of-uninitialized-value options will still report
warning messages against such automatic variables and the compiler will perform
optimization as if the variable were uninitialized. This feature also initializes
padding of automatic structure or union objects to zero. However, automatic variables
that are declared between the controlling expression and the first case of a switch
statement are not initialized. Use the -Wtrivial-auto-var-init option
to report all such cases.
uninitialized- Do not initialize any automatic variables. This choice results in the fastest execution of the program.
pattern- Initialize automatic variables with the value 0xFE. This value is chosen so that logic bugs in the program will more likely result in obvious program crashes, it is easily recognized in crash dumps, and is not a value that programmers rely on for useful program semantics. Note, however, that the value or values used for pattern initialization might changed in future implementations.
zero- Initialize automatic variables with zeroes.
If this option is not specified, the default action is to not initialize automatic
variables, as if the uninitialized choice had been selected.
You can control this behavior for a specific variable by using the
uninitialized variable attribute (see Specifying Attributes of
Variables).