Struct Property 

pub struct Property {
    pub features: u32,
    pub needed: u32,
}

What a file says it was built to have checked, which is what -fcf-protection= asks for.

Design: spec/11-asm-objects-debug.md section 11.3, and spec/04-driver-and-cli.md section 4.7 for the flag.

A machine’s control flow checks are turned on for a whole process or not at all, never for one function, so a program made of one object built with them and one built without has to be run one way or the other. What everybody settled on is that each object records what it was built for, the linker keeps only what every input agreed on, and the loader turns on what is left. So an object that records nothing turns the check off for every object it is linked with, which is why this is written even when the flag changed no instruction in the file.

One number rather than a pair of flags, because that is what the record holds: a word of bits whose meaning is the machine’s, and a linker that has never heard of a bit still knows to drop it when one input does not have it.

Fields

features: u32

The bits of the x86 feature word, which are Self::IBT and Self::SHSTK.

needed: u32

The bits of the word that says what the file needs of the link, which is Self::INDIRECT_EXTERN_ACCESS and nothing else yet. That one is about the code rather than the command line: gcc writes it once nodirect_extern_access was said of a name the file defines or uses.

Implementations

impl Property

pub const X86_FEATURES: u32 = 0xc000_0002

Which property the feature word is, which is the key the record is written under.

pub const IBT: u32 = 1

Indirect branch tracking: every indirect call and jump in the file arrives at a landing pad, so the machine may fault on one that does not.

pub const SHSTK: u32 = 2

The shadow stack: every return in the file goes where a second copy of the return address says it should, so the machine may fault when the two disagree.

pub const NEEDED: u32 = 0xb000_8000

Which property the word of needs is, GNU_PROPERTY_1_NEEDED. Not the machine’s, so it is the same key on every machine, though only x86 writes it.

pub const INDIRECT_EXTERN_ACCESS: u32 = 1

The file reaches a name another object defines only through the global offset table, so the linker must not copy a protected variable into an executable it is part of, and the loader must not bind a protected name in a library to a copy somewhere else.

pub const fn any(self) -> bool

Whether anything is recorded at all, which is whether the record is written.

pub fn each(self) -> impl Iterator<Item = (u32, u32)>

Each property there is something to record for, as its key and its word, in the order gcc writes them, which is one note each.

Trait Implementations

impl Clone for Property

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Property

impl Debug for Property

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

Formats the value using the given formatter.

impl Default for Property

fn default() -> Self

Returns the “default value” for a type.

impl Eq for Property

impl PartialEq for Property

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for Property