Skip to content

Block signatures #765

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
sunfishcode merged 3 commits into from
Sep 14, 2016
Merged

Block signatures #765

Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
fb1f010
Replace branch arities with block and if signatures.
sunfishcode Aug 9, 2016
dcd2a3a
Remove the arity operand from br_table too.
sunfishcode Sep 9, 2016
2bee76f
Remove mentions of "arguments".
sunfishcode Sep 12, 2016
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
22 changes: 15 additions & 7 deletions BinaryEncoding.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,14 @@ A single-byte unsigned integer indicating a [value type](AstSemantics.md#types).
* `3` indicating type `f32`
* `4` indicating type `f64`

### `inline_signature_type`
A single-byte unsigned integer indicating a signature. These types are encoded as:
Copy link

@titzer titzer Sep 12, 2016

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This will be simpler to explain in terms of a single result time, since the signatures won't be relevant until some future post-MVP version.

* `0` indicating a signature with 0 results.
* `1` indicating a signature with 1 result of type `i32`.
* `2` indicating a signature with 1 result of type `i64`.
* `3` indicating a signature with 1 result of type `f32`.
* `4` indicating a signature with 1 result of type `f64`.

### `external_kind`
A single-byte unsigned integer indicating the kind of definition being imported or defined:
* `0` indicating a `Function` [import](Modules.md#imports) or [definition](Modules.md#function-and-code-sections)
Expand Down Expand Up @@ -436,26 +444,26 @@ It is legal to have several entries with the same type.
| Name | Opcode | Immediates | Description |
| ---- | ---- | ---- | ---- |
| `unreachable` | `0x00` | | trap immediately |
| `block` | `0x01` | | begin a sequence of expressions, the last of which yields a value |
| `loop` | `0x02` | | begin a block which can also form control flow loops |
| `if` | `0x03` | | begin if expression |
| `block` | `0x01` | sig : `inline_signature_type` | begin a sequence of expressions, yielding 0 or 1 values |
Copy link

@ghost ghost Sep 9, 2016

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

There does not appear to be any compelling reason to restrict blocks to returning only '0 or 1 values` in the MVP. It is probably a small matter for the runtimes to be able to return multiple values here? But don't let that hold this up, can always revisit how it is going.

Also no mention if a function signature with arguments is usable in the MVP? Also seems a small matter, just not sure if it is really necessary yet.

| `loop` | `0x02` | sig : `inline_signature_type` | begin a block which can also form control flow loops |
| `if` | `0x03` | sig : `inline_signature_type` | begin if expression |
| `else` | `0x04` | | begin else expression of if |
| `select` | `0x05` | | select one of two values based on condition |
| `br` | `0x06` | arity : `varuint1`, relative_depth : `varuint32` | break that targets an outer nested block |
| `br_if` | `0x07` | arity : `varuint1`, relative_depth : `varuint32` | conditional break that targets an outer nested block |
| `br` | `0x06` | relative_depth : `varuint32` | break that targets an outer nested block |
| `br_if` | `0x07` | relative_depth : `varuint32` | conditional break that targets an outer nested block |
| `br_table` | `0x08` | see below | branch table control flow construct |
| `return` | `0x09` | return zero or one value from this function |
| `drop` | `0x0b` | | ignore value |
| `nop` | `0x0a` | | no operation |
| `end` | `0x0f` | | end a block, loop, or if |

The counts following the break operators specify how many operands are taken as transfer arguments; in the MVP, all these values must be either 0 or 1.
The _sig_ fields of `block` and `if` operators specify function signatures
which describe their use of the operand stack.

The `br_table` operator has an immediate operand which is encoded as follows:

Copy link
Member

@rossberg rossberg Sep 9, 2016

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

The br_table immediate needs the arity removed, too.

| Field | Type | Description |
| ---- | ---- | ---- |
| arity | `varuint1` | number of arguments |
| target_count | `varuint32` | number of entries in the target_table |
| target_table | `varuint32*` | target entries that indicate an outer block or loop to which to break |
| default_target | `varuint32` | an outer block or loop to which to break in the default case |
Expand Down