tree 37fdc8da042bdb90d34e9b3b9f553fea5f2b14a7
parent 68281cd416055538afe4d39e222e939fe03536cf
author Yuta Saito <kateinoigakukun@gmail.com> 1708454136 +0900
committer Copybara-Service <copybara-worker@google.com> 1708454518 -0800

[WebAssembly] Add segment RETAIN flag to support private retained data (#81539)

In WebAssembly, we have `WASM_SYMBOL_NO_STRIP` symbol flag to mark the
referenced content as retained. However, the flag is not enough to
express retained data that is not referenced by any symbol. This patch
adds a new segment flag`WASM_SEG_FLAG_RETAIN` to support "private"
linkage data that is retained by llvm.used.

This kind of data that is not referenced but must be retained is usually
used with encapsulation symbols (__start/__stop). Swift runtime uses
this technique and depends on the fact "all metadata sections in live
objects are retained", which was not guaranteed with `--gc-sections`
before this patch.

This is a revised version of https://reviews.llvm.org/D126950 (has been
reverted) based on @MaskRay's comments

GitOrigin-RevId: ba3c1f9ce30cf4f8aee5f1961df74d65e11d53bc