fluencelabs/wasm-utils
1
0
Fork 0
mirror of https://github.com/fluencelabs/wasm-utils synced 2025-03-14 18:50:52 +00:00
Code Issues Projects Releases Wiki Activity

!fixup lowest_forward_br rename and field docs.

Browse Source
This commit is contained in:
Jim Posen 2019-07-12 10:39:57 +02:00
parent 93abbcfe56
commit 82bd972333
1 changed files with 12 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
src/gas.rs
View File

@ -42,12 +42,13 @@ pub fn update_call_index(instructions: &mut elements::Instructions, inserted_ind
struct ControlBlock {
/// The lowest control stack index corresponding to a forward jump targeted by a br, br_if, or
/// br_table instruction within this control block. The index must refer to a control block
/// that is not a loop, meaning it is a forward jump.
/// that is not a loop, meaning it is a forward jump. Given the way Wasm control flow is
/// structured, the lowest index on the stack represents the furthest forward branch target.
///
/// This value will always be at most the index of the block itself, even if there is no
/// explicit br instruction targeting this control block. This does not affect how the value is
/// used in the metering algorithm.
lowest_forward_br: usize,
lowest_forward_br_target: usize,
/// The active metering block that new instructions contribute a gas cost towards.
active_metered_block: MeteredBlock,
@ -94,7 +95,7 @@ impl Counter {
fn begin_control_block(&mut self, cursor: usize, is_loop: bool) {
let index = self.stack.len();
self.stack.push(ControlBlock {
lowest_forward_br: index,
lowest_forward_br_target: index,
active_metered_block: MeteredBlock {
start_pos: cursor,
cost: 0,
@ -118,17 +119,18 @@ impl Counter {
return Ok(())
}
// Update the lowest_forward_br for the control block now on top of the stack.
// Update the lowest_forward_br_target for the control block now on top of the stack.
{
let control_block = self.stack.last_mut().ok_or_else(|| ())?;
control_block.lowest_forward_br = min(
control_block.lowest_forward_br, closing_control_block.lowest_forward_br
control_block.lowest_forward_br_target = min(
control_block.lowest_forward_br_target,
closing_control_block.lowest_forward_br_target
);
}
// If there may have been a branch to a lower index, then also finalize the active metered
// block for the previous control block. Otherwise, finalize it and begin a new one.
let may_br_out = closing_control_block.lowest_forward_br < closing_control_index;
let may_br_out = closing_control_block.lowest_forward_br_target < closing_control_index;
if may_br_out {
self.finalize_metered_block(cursor)?;
}
@ -180,7 +182,7 @@ impl Counter {
fn branch(&mut self, cursor: usize, indices: &[usize]) -> Result<(), ()> {
self.finalize_metered_block(cursor)?;
// Update the lowest_forward_br of the current control block.
// Update the lowest_forward_br_target of the current control block.
for &index in indices {
let target_is_loop = {
let target_block = self.stack.get(index).ok_or_else(|| ())?;
@ -191,7 +193,8 @@ impl Counter {
}
let control_block = self.stack.last_mut().ok_or_else(|| ())?;
control_block.lowest_forward_br = min(control_block.lowest_forward_br, index);
control_block.lowest_forward_br_target =
min(control_block.lowest_forward_br_target, index);
}
Ok(())