Enum Control 

pub enum Control {
    None,
    Branch,
    Return,
    Full,
    Check,
}

Which control flow transfers are checked, which is what -fcf-protection= asks.

Two mechanisms and one flag, because the hardware turns them on together and a program built for one and not the other is a program with a hole in whichever half was left out. The forward edge is an indirect call or jump, and it is checked by a landing pad at every address one is allowed to arrive at, so a corrupted function pointer reaches somewhere somebody meant rather than any byte of the program. The backward edge is a return, and it is checked against a second copy of the return address the program cannot write to, which needs no instructions at all: the machine keeps the copy and the loader turns it on.

Which is why the marker matters as much as the code. An object says in a note which halves it was built for, the linker takes the intersection over every input, and the loader turns on what survives. One object built without the note is enough to turn the whole program’s protection off, so the note goes in even for a mode that changes no instruction.

Variants

None

-fcf-protection=none and -fno-cf-protection, and what a command line that says nothing gets. gcc’s own default is the same on the targets this compiler has a back end for.

Branch

-fcf-protection=branch. The forward edge alone: a landing pad at every function, and a note that asks for the check on indirect transfers and not on returns.

Return

-fcf-protection=return. The backward edge alone, which is the note and nothing else, since the copy of the return address is the machine’s own and no instruction maintains it.

Full

-fcf-protection=full, and what the bare -fcf-protection means. Both halves.

Check

-fcf-protection=check. Asks that the compilation be checked for compatibility with the mode rather than built in it, so nothing is instrumented and no note is written, which is exactly what gcc emits for it.

Implementations

impl Control

pub const fn branch(self) -> bool

Whether a landing pad goes at the top of every function.

pub const fn ret(self) -> bool

Whether returns are asked to be checked against the machine’s own copy.

pub const fn any(self) -> bool

Whether anything at all is asked for, which is what decides whether the file says what it was built for.

False for the two modes that build nothing. Control::None asks for nothing and Control::Check asks that the compilation be looked at rather than changed, and gcc writes no note for either.

pub const fn as_str(self) -> &'static str

What the argument was spelled as, which is the part after the equals sign.

Trait Implementations

impl Clone for Control

fn clone(&self) -> Control

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Control

impl Debug for Control

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Control

fn default() -> Control

Returns the “default value” for a type.

impl Display for Control

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for Control

impl FromStr for Control

fn from_str(s: &str) -> Result<Self, ()>

Parses the part after -fcf-protection=.

type Err = ()

The associated error which can be returned from parsing.

impl Hash for Control

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for Control

fn cmp(&self, other: &Control) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

fn clamp_to<R>(self, range: R) -> Self

where Self: Sized, R: ClampBounds<Self>,

🔬This is a nightly-only experimental API. (clamp_to)

Restrict a value to a certain range.

impl PartialEq for Control

fn eq(&self, other: &Control) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl PartialOrd for Control

fn partial_cmp(&self, other: &Control) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl StructuralPartialEq for Control