I am using rust-lldb to explore function item & function pointer in Rust. The code is very simple:

// src/main.rs


#[inline(never)]
fn add(a: i32, b: i32) -> i32 {
    a + b
}

#[inline(never)]
fn sub(a: i32, b: i32) -> i32 {
    a - b
}

fn main() {
    let item = add; // function item
    let item1 = sub; // function item

    let ptr: fn(i32, i32) -> i32 = add; // function pointer
    let x = item(1, 2);
    let y = item1(3, 2);
    let z = ptr(1, 2);
    assert_eq!(3, x);
    assert_eq!(1, y);
    assert_eq!(3, z);
}

When I set a breakpoint and start debugging, I found that both item & item1 points to an invalid address

➜  function git:(master) ✗ rust-lldb --version
lldb-1500.0.404.7
Apple Swift version 5.10 (swiftlang-5.10.0.13 clang-1500.3.9.4)
➜  function git:(master) ✗ rustc -g -C opt-level=0 src/main.rs -o main
➜  function git:(master) ✗ rust-lldb main                             
(lldb) command script import "/Users/caelansar/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/etc/lldb_lookup.py"
(lldb) command source -s 0 '/Users/caelansar/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/etc/lldb_commands'
Executing commands in '/Users/caelansar/.rustup/toolchains/nightly-aarch64-apple-darwin/lib/rustlib/etc/lldb_commands'.
(lldb) type synthetic add -l lldb_lookup.synthetic_lookup -x ".*" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^(alloc::([a-z_]+::)+)String$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^&(mut )?str$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^&(mut )?\[.+\]$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^(std::ffi::([a-z_]+::)+)OsString$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^(alloc::([a-z_]+::)+)Vec<.+>$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^(alloc::([a-z_]+::)+)VecDeque<.+>$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^(alloc::([a-z_]+::)+)BTreeSet<.+>$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^(alloc::([a-z_]+::)+)BTreeMap<.+>$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^(std::collections::([a-z_]+::)+)HashMap<.+>$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^(std::collections::([a-z_]+::)+)HashSet<.+>$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^(alloc::([a-z_]+::)+)Rc<.+>$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^(alloc::([a-z_]+::)+)Arc<.+>$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^(core::([a-z_]+::)+)Cell<.+>$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^(core::([a-z_]+::)+)Ref<.+>$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^(core::([a-z_]+::)+)RefMut<.+>$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^(core::([a-z_]+::)+)RefCell<.+>$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^(core::([a-z_]+::)+)NonZero<.+>$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^core::num::([a-z_]+::)*NonZero.+$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^(std::([a-z_]+::)+)PathBuf$" --category Rust
(lldb) type summary add -F lldb_lookup.summary_lookup  -e -x -h "^&(mut )?(std::([a-z_]+::)+)Path$" --category Rust
(lldb) type category enable Rust
(lldb) target create "main"
Current executable set to '/Users/caelansar/RustroverProjects/function/main' (arm64).
(lldb) b 18
Breakpoint 1: where = main`main::main::h8d79616f9b6b86ce + 96 at main.rs:18:13, address = 0x000000010000169c
(lldb) r
Process 96136 launched: '/Users/caelansar/RustroverProjects/function/main' (arm64)
Process 96136 stopped
* thread #1, name = 'main', queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    frame #0: 0x000000010000169c main`main::main::h8d79616f9b6b86ce at main.rs:18:13
   15       let ptr: fn(i32, i32) -> i32 = add; // function pointer
   16       let x = item(1, 2);
   17       let y = item1(3, 2);
-> 18       let z = ptr(1, 2);
   19       assert_eq!(3, x);
   20       assert_eq!(1, y);
   21       assert_eq!(3, z);
Target 0: (main) stopped.
(lldb) v
(int (*)(int, int)) item = 0x0001000000030000
(int (*)(int, int)) item1 = 0x0000010000000300
(int (*)(int, int)) ptr = 0x00000001000015b4 (main`main::add::h243b87047811e43e at main.rs:2)
(int) x = 3
(int) y = 1
(lldb) n
Process 96136 stopped
* thread #1, name = 'main', queue = 'com.apple.main-thread', stop reason = step over
    frame #0: 0x00000001000016b8 main`main::main::h8d79616f9b6b86ce at main.rs:19:5
   16       let x = item(1, 2);
   17       let y = item1(3, 2);
   18       let z = ptr(1, 2);
-> 19       assert_eq!(3, x);
   20       assert_eq!(1, y);
   21       assert_eq!(3, z);
   22   }
Target 0: (main) stopped.
(lldb) v
(int (*)(int, int)) item = 0x0001000000030000
(int (*)(int, int)) item1 = 0x0000010000000300
(int (*)(int, int)) ptr = 0x00000001000015b4 (main`main::add::h243b87047811e43e at main.rs:2)
(int) x = 3
(int) y = 1
(int) z = 3
(lldb) 

What does the address 0x0001000000030000 / 0x0000010000000300 represent? They don’t seem to be addresses of function instructions.

Not sure if it’s related to the OS, I’m using an Apple Silicon MBP.