Struct Peb 

#[repr(C)]
pub struct Peb {
    pub _reserved1: [u8; 2],
    pub being_debugged: u8,
    pub _reserved2: [u8; 1],
    pub _reserved3: [*mut c_void; 2],
    pub ldr: *mut PebLdrData,
}

PEB prefix through Ldr.

winternl.h: BYTE Reserved1[2], BYTE BeingDebugged, BYTE Reserved2[1], PVOID Reserved3[2], PPEB_LDR_DATA Ldr. repr(C) supplies the 4-byte x64 alignment pad after Reserved2, so Ldr lands at 0x18 on x64 and 0x0C on x86. Source: https://learn.microsoft.com/en-us/windows/win32/api/winternl/ns-winternl-peb

Fields

_reserved1: [u8; 2]

being_debugged: u8

_reserved2: [u8; 1]

_reserved3: [*mut c_void; 2]

ldr: *mut PebLdrData