Overlink is a simple library that works to override linked C functions, while also keeping it conventient to delegate to the function being overridden.
To override an existing C function, just use the #[overlink] attribute:
#[overlink]
unsafe extern fn time(arg: *mut time_t) -> time_t {
let result = super!(arg);
println!("time -> {result:?}");
result
}The super! macro allows you to call the original function from within the
#[overlink] function.
#[overlink(name = "symbol_name")] can be used to specify a linked/exported name
that is different from the function name:
#[overlink(name = "time")]
unsafe extern fn custom_time(arg: *mut time_t) -> time_t {
// ...
}By default, the symbol name is the same as the function name (effectively working
like #[no_mangle]).
By default, if the function is called within itself, it will automatically call
the overridden function itself. This is to protect from cases where a overridden
function is indirectly called from within the #[overlink] function, causing an
unintented recursive loop.
#[overlink(allow_reentry)] can be used to disable this behavior.
Caution
When the default behavior is disabled, you must take care to ensure that the function does not create an uncontrolled recursive loop, as this may lead to stack overflow.