wasm-linker: finish shared-memory & TLS implementation #16439
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andrewrk
approved these changes
Jul 19, 2023
Rather than verifying if importing memory is false, we now rely on the option that was passed to the CLI (where export is defaulted to `true` unless only import-memory is given).
Implements the `start` section which will execute a given function at startup of the program. After function execution, the _start function will be called by the runtime. In the case of shared-memory we set this section to the function `__wasm_init_memory` which will initialize all memory on startup. This also fixes the above mentioned function to ensure we correctly lower the i32 values. Lastly, this fixes a typo where we would retrieve a global, instead of setting its value.
Previously, they were only created when we had any TLS segment. This meant that while the symbol existed, the global itself wouldn't. The result of this was a crash during symbol names writing as it would attempt to write the symbol name of a global that didn't exist. Now we always create them, and instead update its `init` value during `setupMemory`. In the future, the entire symbol (and global) will be removed by the garbage collector.
This was referenced Jul 23, 2023
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This fixes several bugs in the shared-memory implementation and adds TLS relocations which was the last component required to get the shared-memory linker feature fully working.
With this PR, we can now use the self-hosted WebAssembly linker to link the threading example from: #16207 (i.e. appending
-fno-LLDto the listed command).