forked from AbleOS/holey-bytes
Moved lore
This commit is contained in:
parent
ee5a972921
commit
db2e5de20b
|
@ -47,31 +47,32 @@ impl Assembler {
|
||||||
}
|
}
|
||||||
|
|
||||||
/// Append 12 zeroes (UN) at the end
|
/// Append 12 zeroes (UN) at the end
|
||||||
|
///
|
||||||
|
/// # HBVM lore
|
||||||
|
///
|
||||||
|
/// In reference HBVM implementation checks are done in
|
||||||
|
/// a separate phase before execution.
|
||||||
|
///
|
||||||
|
/// This way execution will be much faster as they have to
|
||||||
|
/// be done only once.
|
||||||
|
///
|
||||||
|
/// There was an issue. You cannot statically check register values and
|
||||||
|
/// `JAL` instruction could hop at the end of program to some byte, which
|
||||||
|
/// will be interpreted as opcode and VM in attempt to decode the instruction
|
||||||
|
/// performed out-of-bounds read which leads to undefined behaviour.
|
||||||
|
///
|
||||||
|
/// Several options were considered to overcome this, but inserting some data at
|
||||||
|
/// program's end which when executed would lead to undesired behaviour, though
|
||||||
|
/// not undefined behaviour.
|
||||||
|
///
|
||||||
|
/// Newly created `UN` (as UNreachable) was chosen as
|
||||||
|
/// - It was a good idea to add some equivalent to `ud2` anyways
|
||||||
|
/// - It was chosen to be zero
|
||||||
|
/// - What if you somehow reached that code, it will appropriately bail :)
|
||||||
|
/// - (yes, originally `NOP` was considered)
|
||||||
|
///
|
||||||
|
/// Why 12 bytes? That's the size of largest instruction parameter part.
|
||||||
pub fn finalise(&mut self) {
|
pub fn finalise(&mut self) {
|
||||||
// HBVM lore:
|
|
||||||
//
|
|
||||||
// In reference HBVM implementation checks are done in
|
|
||||||
// a separate phase before execution.
|
|
||||||
//
|
|
||||||
// This way execution will be much faster as they have to
|
|
||||||
// be done only once.
|
|
||||||
//
|
|
||||||
// There was an issue. You cannot statically check register values and
|
|
||||||
// `JAL` instruction could hop at the end of program to some byte, which
|
|
||||||
// will be interpreted as opcode and VM in attempt to decode the instruction
|
|
||||||
// performed out-of-bounds read which leads to undefined behaviour.
|
|
||||||
//
|
|
||||||
// Several options were considered to overcome this, but inserting some data at
|
|
||||||
// program's end which when executed would lead to undesired behaviour, though
|
|
||||||
// not undefined behaviour.
|
|
||||||
//
|
|
||||||
// Newly created `UN` (as UNreachable) was chosen as
|
|
||||||
// - It was a good idea to add some equivalent to `ud2` anyways
|
|
||||||
// - It was chosen to be zero
|
|
||||||
// - What if you somehow reached that code, it will appropriately bail :)
|
|
||||||
// - (yes, originally NOP was considered)
|
|
||||||
//
|
|
||||||
// Why 12 bytes? That's the size of largest instruction parameter part.
|
|
||||||
self.buf.extend([0; 12]);
|
self.buf.extend([0; 12]);
|
||||||
}
|
}
|
||||||
}
|
}
|
||||||
|
|
Loading…
Reference in a new issue