使用-fvisibility = hidden隐藏C ++符号 [英] Hiding C++ symbols with -fvisibility=hidden

问题描述

我有一个带有C API的C ++库，并且设置了-fvisibility=hidden编译器标志， 然后我在C API方法上设置了__attribute__ ((visibility ("default"))).

但是，我仍然看到可见的C ++符号.当我为我的图书馆创建一个Debian软件包时， 我得到以下符号文件

为什么这些符号仍然可见?

解决方案

您应该通过c++filt运行符号文件，该文件会将乱码"符号名称转换为[在c++意义上来说]可读的名称.

如果这样做，您会发现三分之二的符号是std::whatever，而不是您的符号.因此，由于STL，它们被拉入.您可能无法控制它们.

如果有帮助，其他符号为grk _ *.

有些目标文件实用程序(例如readelf，objdump，objcopy等)可以使您编辑/修补目标文件.

或者，您也许可以使用链接描述文件.

或者，您可以使用-S进行编译以获得.s文件.然后，您可以编写[perl/python]脚本来修改asm源并添加/更改需要更改可见性的任何属性.然后，只需执行:c++ -c modified.s

---

对于给定的符号(例如):

int __attribute__((visibility("hidden")))
main(void)
{

    return 0;
}

---

asm文件为:

    .file   "main.c"
    .text
    .globl  main
    .hidden main
    .type   main, @function
main:
.LFB0:
    .cfi_startproc
    pushq   %rbp
    .cfi_def_cfa_offset 16
    .cfi_offset 6, -16
    movq    %rsp, %rbp
    .cfi_def_cfa_register 6
    movl    $0, %eax
    popq    %rbp
    .cfi_def_cfa 7, 8
    ret
    .cfi_endproc
.LFE0:
    .size   main, .-main
    .ident  "GCC: (GNU) 8.3.1 20190223 (Red Hat 8.3.1-2)"
    .section    .note.GNU-stack,"",@progbits

注意asm指令:

.hidden main

即使没有这样的指令，也应该很容易编写一个脚本来添加一个脚本[在相应的.globl之后

I have a C++ library with a C API, and I have set the -fvisibility=hidden compiler flag, and then I have set __attribute__ ((visibility ("default"))) on C API methods.

However, I still see visible C++ symbols. When I create a debian package for my library, I get the following symbols file

Why are these symbols still visible ?

解决方案

You should run your symbols file through c++filt which converts the "mangled" symbol names to what is readable [in the c++ sense].

If you do, you'll find that two thirds of the symbols are std::whatever, and not your symbols. So, they are being pulled in because of the STL. You may not be able to control them.

The other symbols are grk_*, if that helps.

There are object file utilities (e.g. readelf, objdump, objcopy, etc) that may allow you to edit/patch your object files.

Or, you might be able to use a linker script.

Or, you could compile with -S to get a .s file. You could then write a [perl/python] script to modify the asm source and add/change whatever attribute(s) you need to change the visibility. Then, just do: c++ -c modified.s

---

For a given symbol (e.g.):

int __attribute__((visibility("hidden")))
main(void)
{

    return 0;
}

---

The asm file is:

    .file   "main.c"
    .text
    .globl  main
    .hidden main
    .type   main, @function
main:
.LFB0:
    .cfi_startproc
    pushq   %rbp
    .cfi_def_cfa_offset 16
    .cfi_offset 6, -16
    movq    %rsp, %rbp
    .cfi_def_cfa_register 6
    movl    $0, %eax
    popq    %rbp
    .cfi_def_cfa 7, 8
    ret
    .cfi_endproc
.LFE0:
    .size   main, .-main
    .ident  "GCC: (GNU) 8.3.1 20190223 (Red Hat 8.3.1-2)"
    .section    .note.GNU-stack,"",@progbits

Notice the asm directive:

.hidden main

Even without such a directive, it should be easy to write a script to add one [after the corresponding .globl]

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