1 DESCRIPTION ------------------------------------------------------------------- 2 3 gcmole is a simple static analysis tool used to find possible evaluation order 4 dependent GC-unsafe places in the V8 codebase. 5 6 For example the following code is GC-unsafe: 7 8 Handle<Object> Foo(); // Assume Foo can trigger a GC. 9 void Bar(Object*, Object*); 10 11 Handle<Object> baz; 12 baz->Qux(*Foo()); // (a) 13 Bar(*Foo(), *baz); // (b) 14 15 Both in cases (a) and (b) compiler is free to evaluate call arguments (that 16 includes receiver) in any order. That means it can dereference baz before 17 calling to Foo and save a raw pointer to a heap object in the register or 18 on the stack. 19 20 PREREQUISITES ----------------------------------------------------------------- 21 22 1) Install Lua 5.1 23 24 2) Get LLVM 2.9 and Clang 2.9 sources and build them. 25 26 Follow the instructions on http://clang.llvm.org/get_started.html. 27 28 Make sure to pass --enable-optimized to configure to get Release build 29 instead of a Debug one. 30 31 3) Build gcmole Clang plugin (libgcmole.so) 32 33 In the tools/gcmole execute the following command: 34 35 LLVM_SRC_ROOT=<path-to-llvm-source-root> make 36 37 USING GCMOLE ------------------------------------------------------------------ 38 39 gcmole consists of driver script written in Lua and Clang plugin that does 40 C++ AST processing. Plugin (libgcmole.so) is expected to be in the same 41 folder as driver (gcmole.lua). 42 43 To start analysis cd into the root of v8 checkout and execute the following 44 command: 45 46 CLANG_BIN=<path-to-clang-bin-folder> lua tools/gcmole/gcmole.lua [<arch>] 47 48 where arch should be one of architectures supported by V8 (arm, ia32, x64). 49 50 Analysis will be performed in 2 stages: 51 52 - on the first stage driver will parse all files and build a global callgraph 53 approximation to find all functions that might potentially cause GC, list 54 of this functions will be written into gcsuspects file. 55 56 - on the second stage driver will parse all files again and will locate all 57 callsites that might be GC-unsafe based on the list of functions causing GC. 58 Such places are marked with a "Possible problem with evaluation order." 59 warning. Messages "Failed to resolve v8::internal::Object" are benign and 60 can be ignored. 61 62 If any errors were found driver exits with non-zero status. 63
