当clang编译到目标wasm时未定义的符号

Question

所以我设法让一些简单的 webassembly 应用程序在浏览器中运行，我设法从 Javascript 调用 webassembly 代码。但是，当我尝试从 C 代码调用 Javascript 时，我无法编译代码

我正在使用 clang 9.0 和 wasi-libc。我是如何编译的：

clang --target=wasm32-wasi -Wl,--allow-undefined-file=src/wasm.syms -Wl,--export-all --sysroot wasm-test/wasi-libc/sysroot -O2 - s -o ./public/main.wasm ./src/main.cpp

src/main.cpp:

#include <stdio.h>

void __console_log(int str, int len);

int main()
{
    printf("MAIN!\n");
    return 0;
}

extern "C"
{
    void test()
    {
        char *str = "TEST!";
        __console_log((int)str, 5);
    }

    int test2()
    {
        return 10;
    }
}

wasm.syms：

__console_log

如果我在 cpp 文件中删除对 __console_log 的引用，它可以工作，但是当我添加它时，即使我在命令行中有 --allow-undefined-file=src/wasm.syms，我仍然会收到链接错误（也尝试使用 -U=__console_log ，同样的错误）：

wasm-ld: error: /var/folders/vl/4bjdkcfx1gncfx0vzrl0s57c0000gn/T/main-a723f9.o: undefined symbol: __console_log(int, int)

这是使用 -v 标志运行时的完整日志：

$ clang --target=wasm32-wasi -Wl,--allow-undefined-file=src/wasm.syms -Wl,--export-all --sysroot /Users/hoff/dev/wasm-test/wasi-libc/sysroot -O2 -s -o ./public/main.wasm ./src/main.cpp -v
clang version 9.0.0 (git://github.com/llvm/llvm-project.git 0399d5a9682b3cef71c653373e38890c63c4c365)
Target: wasm32-unknown-wasi
Thread model: posix
InstalledDir: /Users/hoff/dev/wasm-test/clang/bin
 "/Users/hoff/dev/wasm-test/clang/bin/clang-9" -cc1 -triple wasm32-unknown-wasi -emit-obj -disable-free -disable-llvm-verifier -discard-value-names -main-file-name main.cpp -mrelocation-model static -mthread-model posix -masm-verbose -mconstructor-aliases -fuse-init-array -target-cpu generic -fvisibility hidden -dwarf-column-info -debugger-tuning=gdb -target-linker-version 512.4 -momit-leaf-frame-pointer -v -resource-dir /Users/hoff/dev/wasm-test/clang/lib/clang/9.0.0 -isysroot /Users/hoff/dev/wasm-test/wasi-libc/sysroot -internal-isystem /Users/hoff/dev/wasm-test/wasi-libc/sysroot/include/wasm32-wasi/c++/v1 -internal-isystem /Users/hoff/dev/wasm-test/wasi-libc/sysroot/include/c++/v1 -internal-isystem /Users/hoff/dev/wasm-test/clang/lib/clang/9.0.0/include -internal-isystem /Users/hoff/dev/wasm-test/wasi-libc/sysroot/include/wasm32-wasi -internal-isystem /Users/hoff/dev/wasm-test/wasi-libc/sysroot/include -O2 -fdeprecated-macro -fdebug-compilation-dir /Users/hoff/dev/wasm-test -ferror-limit 19 -fmessage-length 102 -fobjc-runtime=gnustep -fcxx-exceptions -fexceptions -fno-common -fdiagnostics-show-option -fcolor-diagnostics -vectorize-loops -vectorize-slp -o /var/folders/vl/4bjdkcfx1gncfx0vzrl0s57c0000gn/T/main-a723f9.o -x c++ ./src/main.cpp
clang -cc1 version 9.0.0 based upon LLVM 9.0.0 default target x86_64-apple-darwin17.6.0
ignoring nonexistent directory "/Users/hoff/dev/wasm-test/wasi-libc/sysroot/include/wasm32-wasi/c++/v1"
ignoring nonexistent directory "/Users/hoff/dev/wasm-test/wasi-libc/sysroot/include/c++/v1"
ignoring nonexistent directory "/Users/hoff/dev/wasm-test/wasi-libc/sysroot/include/wasm32-wasi"
#include "..." search starts here:
#include <...> search starts here:
 /Users/hoff/dev/wasm-test/clang/lib/clang/9.0.0/include
 /Users/hoff/dev/wasm-test/wasi-libc/sysroot/include
End of search list.
./src/main.cpp:17:21: warning: ISO C++11 does not allow conversion from string literal to 'char *'
      [-Wwritable-strings]
        char *str = "TEST!";
                    ^
1 warning generated.
 "/Users/hoff/dev/wasm-test/clang/bin/wasm-ld" --strip-all -L/Users/hoff/dev/wasm-test/wasi-libc/sysroot/lib/wasm32-wasi /Users/hoff/dev/wasm-test/wasi-libc/sysroot/lib/wasm32-wasi/crt1.o --allow-undefined-file=src/wasm.syms --export-all /var/folders/vl/4bjdkcfx1gncfx0vzrl0s57c0000gn/T/main-a723f9.o -lc /Users/hoff/dev/wasm-test/clang/lib/clang/9.0.0/lib/wasi/libclang_rt.builtins-wasm32.a -o ./public/main.wasm
wasm-ld: error: /var/folders/vl/4bjdkcfx1gncfx0vzrl0s57c0000gn/T/main-a723f9.o: undefined symbol: __console_log(int, int)
clang-9: error: linker command failed with exit code 1 (use -v to see invocation)

感谢任何帮助。

Answer 1

您还需要将__console_log 声明为外部“C”。该线索在于函数签名包含在错误消息中。 lld 在这里要求 C++ 符号（如果没有，也许会更清楚，我不确定）。