llvm-project/clang
Guanzhong Chen 42bba4b852 [WebAssembly] Implement thread-local storage (local-exec model)
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
2019-07-16 22:00:45 +00:00
..
INPUTS
bindings [clang][Tooling] Infer target and mode from argv[0] when using JSONCompilationDatabase 2019-06-26 07:39:03 +00:00
cmake [CMake][Fuchsia] Define asan+noexcept multilib 2019-07-13 08:07:10 +00:00
docs Finish "Adapt -fsanitize=function to SANITIZER_NON_UNIQUE_TYPEINFO" 2019-07-16 06:23:27 +00:00
examples cmake: Add CLANG_LINK_CLANG_DYLIB option 2019-07-03 22:45:55 +00:00
include [WebAssembly] Implement thread-local storage (local-exec model) 2019-07-16 22:00:45 +00:00
lib [WebAssembly] Implement thread-local storage (local-exec model) 2019-07-16 22:00:45 +00:00
runtime [GWP-ASan] Mutex implementation [2]. 2019-05-30 19:45:32 +00:00
test [WebAssembly] Implement thread-local storage (local-exec model) 2019-07-16 22:00:45 +00:00
tools [clang-scan-view] Force utf-8 when handling report (python2 only) 2019-07-16 08:56:47 +00:00
unittests [clang-format] Don't detect call to ObjC class method as C++11 attribute specifier 2019-07-16 21:29:40 +00:00
utils [OpenCL] Make TableGen'd builtin tables and helper functions static 2019-07-15 22:34:19 +00:00
www Retire VS2015 Support 2019-07-09 10:12:37 +00:00
.arcconfig
.clang-format
.clang-tidy Disable tidy checks with too many hits 2019-02-01 11:20:13 +00:00
.gitignore Adjust documentation for git migration. 2019-01-29 16:37:27 +00:00
CMakeLists.txt Rename libclang_shared to libclang-cpp 2019-07-11 21:42:55 +00:00
CODE_OWNERS.TXT
INSTALL.txt
LICENSE.TXT Fix typos throughout the license files that somehow I and my reviewers 2019-01-21 09:52:34 +00:00
ModuleInfo.txt
NOTES.txt
README.txt [NFC] Test commit 2019-06-12 07:50:48 +00:00

README.txt

//===----------------------------------------------------------------------===//
// C Language Family Front-end
//===----------------------------------------------------------------------===//

Welcome to Clang.  This is a compiler front-end for the C family of languages
(C, C++, Objective-C, and Objective-C++) which is built as part of the LLVM
compiler infrastructure project.

Unlike many other compiler frontends, Clang is useful for a number of things
beyond just compiling code: we intend for Clang to be host to a number of
different source-level tools.  One example of this is the Clang Static Analyzer.

If you're interested in more (including how to build Clang) it is best to read
the relevant web sites.  Here are some pointers:

Information on Clang:             http://clang.llvm.org/
Building and using Clang:         http://clang.llvm.org/get_started.html
Clang Static Analyzer:            http://clang-analyzer.llvm.org/
Information on the LLVM project:  http://llvm.org/

If you have questions or comments about Clang, a great place to discuss them is
on the Clang development mailing list:
  http://lists.llvm.org/mailman/listinfo/cfe-dev

If you find a bug in Clang, please file it in the LLVM bug tracker:
  http://llvm.org/bugs/