使用Emscripten编译SoLoud示例失败，求解决方法

问题描述 #

我正尝试使用Emscripten将个人项目移植到Web端，项目中用到了SoLoud库。编译该库本身没有报错，但编译其simplest示例时出现大量编译错误。

构建库的步骤： #

• 下载并构建genie
• 下载soloud，将genie可执行文件放入build文件夹
• 运行./genie --with-miniaudio-only gmake
• 进入gmake目录并执行emmake make

库编译顺利无错，但执行命令emcc main.cpp libsoloud_static.a -I ../include -o index.html构建simplest示例时，出现以下错误：

emcc: warning: libsoloud_static.a: archive is missing an index; Use emar when creating libraries to ensure an index is created [-Wemcc]
emcc: warning: libsoloud_static.a: adding index [-Wemcc]
error: undefined symbol: _ZN6SoLoud6Soloud19getActiveVoiceCountEv (referenced by top-level compiled C/C++ code)
warning: Link with `-sLLD_REPORT_UNDEFINED` to get more information on undefined symbols
warning: To disable errors for undefined symbols use `-sERROR_ON_UNDEFINED_SYMBOLS=0`
warning: __ZN6SoLoud6Soloud19getActiveVoiceCountEv may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
error: undefined symbol: _ZN6SoLoud6Soloud4initEjjjjj (referenced by top-level compiled C/C++ code)
warning: __ZN6SoLoud6Soloud4initEjjjjj may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
error: undefined symbol: _ZN6SoLoud6Soloud4playERNS_11AudioSourceEffbj (referenced by top-level compiled C/C++ code)
warning: __ZN6SoLoud6Soloud4playERNS_11AudioSourceEffbj may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
error: undefined symbol: _ZN6SoLoud6Soloud6deinitEv (referenced by top-level compiled C/C++ code)
warning: __ZN6SoLoud6Soloud6deinitEv may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
error: undefined symbol: _ZN6SoLoud6SoloudC1Ev (referenced by top-level compiled C/C++ code)
warning: __ZN6SoLoud6SoloudC1Ev may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
error: undefined symbol: _ZN6SoLoud6SoloudD1Ev (referenced by top-level compiled C/C++ code)
warning: __ZN6SoLoud6SoloudD1Ev may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
error: undefined symbol: _ZN6SoLoud6Speech7setTextEPKc (referenced by top-level compiled C/C++ code)
warning: __ZN6SoLoud6Speech7setTextEPKc may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
error: undefined symbol: _ZN6SoLoud6SpeechC1Ev (referenced by top-level compiled C/C++ code)
warning: __ZN6SoLoud6SpeechC1Ev may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
error: undefined symbol: _ZN6SoLoud6SpeechD1Ev (referenced by top-level compiled C/C++ code)
warning: __ZN6SoLoud6SpeechD1Ev may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
error: undefined symbol: _ZN6SoLoud6Thread5sleepEi (referenced by top-level compiled C/C++ code)
warning: __ZN6SoLoud6Thread5sleepEi may need to be added to EXPORTED_FUNCTIONS if it arrives from a system library
Error: Aborting compilation due to previous errors

疑问 #

请问我哪里操作错了？

解决方案 #

这些错误的核心原因是SoLoud库的编译配置未适配Emscripten环境，且链接时未导出必要的符号，具体修正步骤如下：

1. 重新编译适配Emscripten的SoLoud库 #

生成Makefile时需明确指定Emscripten平台，确保编译参数符合WebAssembly要求：

./genie --with-miniaudio-only --platform=emscripten gmake

进入gmake目录后，执行编译并添加位置无关代码参数：

emmake make CXXFLAGS="-fPIC"

-fPIC是WebAssembly静态库的必要参数，确保代码可以正确链接。

2. 链接示例时添加Emscripten专属配置 #

编译示例时，必须导出所有用到的SoLoud符号，并添加Web环境必要参数：

emcc main.cpp libsoloud_static.a -I ../include \
  -sEXPORTED_FUNCTIONS='["_main","_ZN6SoLoud6SoloudC1Ev","_ZN6SoLoud6SoloudD1Ev","_ZN6SoLoud6Soloud4initEjjjjj","_ZN6SoLoud6Soloud6deinitEv","_ZN6SoLoud6Soloud4playERNS_11AudioSourceEffbj","_ZN6SoLoud6Soloud19getActiveVoiceCountEv","_ZN6SoLoud6SpeechC1Ev","_ZN6SoLoud6SpeechD1Ev","_ZN6SoLoud6Speech7setTextEPKc","_ZN6SoLoud6Thread5sleepEi"]' \
  -sEXPORTED_RUNTIME_METHODS='["ccall","cwrap"]' \
  -sALLOW_MEMORY_GROWTH=1 \
  -o index.html

• EXPORTED_FUNCTIONS：将报错中所有未定义的符号添加进去，防止Emscripten编译时剥离这些符号
• EXPORTED_RUNTIME_METHODS：提供JS与C/C++交互的基础接口
• ALLOW_MEMORY_GROWTH：允许WebAssembly内存动态增长，避免内存溢出

3. 修复静态库索引警告 #

如果仍出现库索引缺失的警告，用emar重新生成索引：

emar s libsoloud_static.a

额外提示 #

• SoLoud的Thread::sleep在Web环境下会被Emscripten转换为JS的setTimeout，无需额外修改代码
• 测试时用emrun index.html启动本地服务器，规避浏览器跨域限制

内容的提问来源于stack exchange，提问作者der