Constant wasmtime_environ::ELF_WASMTIME_ADDRMAP

pub const ELF_WASMTIME_ADDRMAP: &str = ".wasmtime.addrmap";

A custom Wasmtime-specific section of our compilation image which stores mapping data from offsets in the image to offset in the original wasm binary.

This section has a custom binary encoding. Currently its encoding is:

• The section starts with a 32-bit little-endian integer. This integer is how many entries are in the following two arrays.
• Next is an array with the previous count number of 32-bit little-endian integers. This array is a sorted list of relative offsets within the text section. This is intended to be a lookup array to perform a binary search on an offset within the text section on this array.
• Finally there is another array, with the same count as before, also of 32-bit little-endian integers. These integers map 1:1 with the previous array of offsets, and correspond to what the original offset was in the wasm file.

Decoding this section is intentionally simple, it only requires loading a 32-bit little-endian integer plus some bounds checks. Reading this section is done with the lookup_file_pos function below. Reading involves performing a binary search on the first array using the index found for the native code offset to index into the second array and find the wasm code offset.

At this time this section has an alignment of 1, which means all reads of it are unaligned. Additionally at this time the 32-bit encodings chosen here mean that >=4gb text sections are not supported.