! WIP !
All integers used for sizes and indexes in this binary formats are in unsigned LEB128 format.
Structure are divided into different sections, each with a specific id, and are order-dependent. Each of the sections are optional and can be skipped. The module starts with a magic number (0x00, 0x61, 0x73, 0x6D) (‘/0asm’ string) and a version number (0x01, 0x00, 0x00, 0x00) (current version of wasm binary format is 1).
| ID | Sections |
|---|---|
| 0 | Custom |
| 1 | Type |
| 2 | Import |
| 3 | Function |
| 4 | Table |
| 5 | Memory |
| 6 | Global |
| 7 | Export |
| 8 | Start |
| 9 | Element |
| 10 | Code |
| 11 | Data |
| 12 | Data count |
Each sections are divided into 3 parts:
All of the sections can be skipped. WASM file that only consist of 8 bytes (0x00, 0x61, 0x73, 0x6D, 0x01, 0x00, 0x00, 0x00) is a valid binary.
Size of each section other than custom can be skipped. Size can be used to skip sections while navigating through a binary. Size of custom section are needed to skip the entire section in case implementation doesn’t support it.
Implementation: Errors in custom sections shouldn’t prevent it from parsing other sections.
!WIP!
This section is used to define signature of all functions. It contains vector of functype. This section look like:
Eg:
| Id | Size | Content |
| | | len | | parameter 1 | result 1 | | parameter 2 | result 2 |
| | | | | len | i32 | f32 | len | f32 | | len | len | f64 |
| 0x01 | 0x09 | 0x02 | 0x60 | 0x02 | 0x7F | 0x7D | 0x01 | 0x7D | 0x60 | 0x0 | 0x01 | 0x7C |
|<------------ function sig. 1 ---------->|<--------- function sig. 2 ------>|Function type defines signature of function and is encoded as:
0x60Eg:
| | parameter | result |
| | len | i32 | f32 | len | f32 |
| 0x60 | 0x02 | 0x7F | 0x7D | 0x01 | 0x7D |It defines function type with 2 parameters (i32 and f32) and single return/result type of f32