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在玩 WebAssembly 时，遇到的坑！提交到issue

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Docker + ubuntu image 编译 emsdk 失败，提示 No CMAKE_CXX_COMPILER could be found

镜像 ubuntu:latest

环境准备, 参考

$ apt update
$ apt install git cmake gcc python

编译

$ git clone https://github.com/juj/emsdk.git
$ cd emsdk
$ ./emsdk install sdk-incoming-64bit binaryen-master-64bit

报错

CMake Error at CMakeLists.txt:47 (project):   No CMAKE_CXX_COMPILER could be found.    Tell CMake where to find the compiler by setting either the environment   variable "CXX" or the CMake cache entry CMAKE_CXX_COMPILER to the full path   to the compiler, or to the compiler name if it is in the PATH.   -- Configuring incomplete, errors occurred! See also "/root/emsdk/clang/fastcomp/build_incoming_64/CMakeFiles/CMakeOutput.log". See also "/root/emsdk/clang/fastcomp/build_incoming_64/CMakeFiles/CMakeError.log". CMake invocation failed due to exception! Working directory: /root/emsdk/clang/fastcomp/build_incoming_64 Command '['cmake', '-G', 'Unix Makefiles', '-DCMAKE_BUILD_TYPE=RelWithDebInfo', '-DPYTHON_EXECUTABLE=/usr/bin/python', '-DLLVM_TARGETS_TO_BUILD=X86;JSBackend', '-DLLVM_INCLUDE_EXAMPLES=OFF', '-DCLANG_INCLUDE_EXAMPLES=OFF', '-DLLVM_INCLUDE_TESTS=OFF', '-DCLANG_INCLUDE_TESTS=OFF', '-DLLVM_ENABLE_ASSERTIONS=ON', '/root/emsdk/clang/fastcomp/src']' returned non-zero exit status 1 Installation failed!

解决

官方的入门指南里只提到gcc，但实际也依赖 g++。一步到位可以安装 build-essential，想要精简可以只安装 cmake gcc 和 g++

所以，安装 g++ 后重新编译

$ apt install g++

解决。

Mac 安装 emscripten 编译报 OSError: [Errno 2] No such file or directory

官网安装 emsdk 的方法比较慢，可以直接安装 emscripten brew install emscripten.
安装完底部有提示需要修改手动修改 ~/.emscripten.
将

LLVM_ROOT = os.path.expanduser(os.getenv('LLVM') or '/usr/bin') # directory
BINARYEN_ROOT = os.path.expanduser(os.getenv('BINARYEN') or '') # directory

修改成

LLVM_ROOT = os.path.expanduser(os.getenv('LLVM') or '/usr/local/opt/emscripten/libexec/llvm/bin') # directory
#BINARYEN_ROOT = os.path.expanduser(os.getenv('BINARYEN') or '') # directory

再运行 emcc -v

在编译过程中，如 emcc hello.c -s WASM=1 -o hello.html，可能会报 OSError: [Errno 2] No such file or directory 的错误，安装 brew install cmake 搞定！

emscripten遇到warning: unresolved symbol: funcName

运行

 emcc -s WASM=1 -O3 -o program.js program.cpp --js-library library.js

warning: unresolved symbol: _Z6funcNamev

program.js

#include <emscripten/emscripten.h>
#include <stack>

// 定义数组大小
#define N 100

// 防止 C++ 函数名被 Mangling
#ifdef _cplusplus
extern "C" {
#endif
    // 预置函数，暴露给 JS 进行处理
    extern void checku ();

    void EMSCRIPTEN_KEEPALIVE abc () {
        char a[] = "username";
        checku();
    }
#ifdef _cplusplus
}
#endif

library.js

mergeInto(LibraryManager.library, {
    checku: function() {
      console.log(123)
    }
});

笔误，踩了一个大坑。

#ifdef _cplusplus
extern "C" {
#endif

其实是 __cplusplus 前面两个下划线

#ifdef __cplusplus
extern "C" {
#endif

添加这个判断防止 C++ 函数名被 Mangling.

urllib2.URLError错误

出现
urllib2.URLError: <urlopen error [Errno 60] Operation timed out>
或者
urllib2.URLError: <urlopen error [Errno 61] Connection refused>
检查当前网络是否能通
是否可以访问https://s3.amazonaws.com/mozilla-games/emscripten/packages/llvm/nightly/linux_32bit/index.txt
然后检查下wget命令是否能正常执行

webassembly-cn / pit Goto Github PK

pit's People

Contributors

Stargazers

Watchers

pit's Issues

Docker + ubuntu image 编译 emsdk 失败，提示 No CMAKE_CXX_COMPILER could be found

Mac 安装 emscripten 编译报 OSError: [Errno 2] No such file or directory

emscripten遇到warning: unresolved symbol: funcName

urllib2.URLError错误

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