forked from OSchip/llvm-project
42bba4b852
Summary:
Thread local variables are placed inside a `.tdata` segment. Their symbols are
offsets from the start of the segment. The address of a thread local variable
is computed as `__tls_base` + the offset from the start of the segment.
`.tdata` segment is a passive segment and `memory.init` is used once per thread
to initialize the thread local storage.
`__tls_base` is a wasm global. Since each thread has its own wasm instance,
it is effectively thread local. Currently, `__tls_base` must be initialized
at thread startup, and so cannot be used with dynamic libraries.
`__tls_base` is to be initialized with a new linker-synthesized function,
`__wasm_init_tls`, which takes as an argument a block of memory to use as the
storage for thread locals. It then initializes the block of memory and sets
`__tls_base`. As `__wasm_init_tls` will handle the memory initialization,
the memory does not have to be zeroed.
To help allocating memory for thread-local storage, a new compiler intrinsic
is introduced: `__builtin_wasm_tls_size()`. This instrinsic function returns
the size of the thread-local storage for the current function.
The expected usage is to run something like the following upon thread startup:
__wasm_init_tls(malloc(__builtin_wasm_tls_size()));
Reviewers: tlively, aheejin, kripken, sbc100
Subscribers: dschuff, jgravelle-google, hiraditya, sunfish, jfb, cfe-commits, llvm-commits
Tags: #clang, #llvm
Differential Revision: https://reviews.llvm.org/D64537
llvm-svn: 366272
|
||
|---|---|---|
| .. | ||
| CMakeLists.txt | ||
| Config.h | ||
| Driver.cpp | ||
| InputChunks.cpp | ||
| InputChunks.h | ||
| InputEvent.h | ||
| InputFiles.cpp | ||
| InputFiles.h | ||
| InputGlobal.h | ||
| LTO.cpp | ||
| LTO.h | ||
| MarkLive.cpp | ||
| MarkLive.h | ||
| Options.td | ||
| OutputSections.cpp | ||
| OutputSections.h | ||
| OutputSegment.h | ||
| Relocations.cpp | ||
| Relocations.h | ||
| SymbolTable.cpp | ||
| SymbolTable.h | ||
| Symbols.cpp | ||
| Symbols.h | ||
| SyntheticSections.cpp | ||
| SyntheticSections.h | ||
| Writer.cpp | ||
| Writer.h | ||
| WriterUtils.cpp | ||
| WriterUtils.h | ||