[PATCH] D126107: [lld][WebAssembly] Allow first-loader to use static TLS region

[Sam Clegg via Phabricator via llvm-commits]

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It turns out we were already allocating space to hold TLS data along
with the rest of the static data, but this space was going unused/ignored.

With this change the `__wasm_init_memory` function (which does the work of
loading the passive segments into memory when a module is first loaded) will now
also call `__wasm_init_tls` with a pointer to the start of the statically
allocated region.

This means that calling `__wasm_init_tls` is longer necessary on the thread the
first loads a moudle.  Calling `__wasm_init_tls` again with a different region
should be harmless enough, making this change backwards compatible.

Practically speaking, this will allow emscripten to avoid dynamic allocation
completely for the first-loader of any DLL.  Crutially this includes the main
module where calling user space functions such as `malloc` is dangerous before
TLS is available.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D126107

Files:
  lld/test/wasm/data-segments.ll
  lld/test/wasm/tls-align.s
  lld/test/wasm/tls.s
  lld/test/wasm/tls_init_symbols.s
  lld/wasm/Driver.cpp
  lld/wasm/Writer.cpp

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