Add GCMole to the repository.

tools/gcmole/README

+DESCRIPTION ---------------------------------------------------------------------
+
+gcmole is a simple static analysis tool used to find possible evaluation order 
+dependent GC-unsafe places in the V8 codebase.
+
+For example the following code is GC-unsafe:
+
+Handle<Object> Foo();  // assume Foo can trigger a GC. 

[Søren Thygesen Gjesse, 2011/04/07 08:20:28]

Start comment with uppercase - even in README :-)

+void Bar(Object*, Object*);
+
+Handle<Object> baz;
+baz->Qux(*Foo());  // (a)  
+Bar(*Foo(), *baz);  // (b)
+
+Both in cases (a) and (b) compiler is free to evaluate call arguments (that 
+includes receiver) in any order. That means it can dereference baz before 
+calling to Foo and save a raw pointer to a heap object in the register or 
+on the stack.  
+
+PREREQUISITES -------------------------------------------------------------------

[Søren Thygesen Gjesse, 2011/04/07 08:20:28]

Long line (few more below).

+
+1) Install Lua 5.1
+
+2) Get LLVM and Clang sources and build them. 
+
+Follow the instructions on http://clang.llvm.org/get_started.html.
+
+Make sure to pass --enable-optimized to configure to get Release build 
+instead of a Debug one.
+
+3) Build gcmole Clang plugin (libgcmole.so)
+
+In the tools/gcmole execute the following command:
+
+LLVM_SRC_ROOT=<path-to-llvm-source-root> make
+
+USING GCMOLE --------------------------------------------------------------------
+
+gcmole consists of driver script written in Lua and Clang plugin that does
+C++ AST processing. Plugin (libgcmole.so) is expected to be in the same
+folder as driver (gcmole.lua).
+
+To start analysis cd into the root of v8 checkout and execute the following command:
+
+CLANG_BIN=<path-to-folder-with-clang-binary> lua tools/gcmole/gcmole.lua [<arch>]
+
+where arch should be one of architectures supported by V8 (arm, ia32, x64).
+
+Analysis will be performed in 2 stages: 
+
+- on the first stage driver will parse all files and build a global callgraph 
+approximation to find all functions that might potentially cause GC, list
+of this functions will be written into gcsuspects file.
+
+- on the second stage driver will parse all files again and will locate all 
+callsites that might be GC-unsafe based on the list of functions causing GC. 
+Such places are marked with a "Possible problem with evaluation order." 
+warning. Messages "Failed to resolve v8::internal::Object" are benign and 
+can be ignored.
+
+If any errors were found driver exits with non-zero status.