c++ - 添加 "extern C"作为符号的编译器选项？

Question

我正在使用支持 FIPS 的 OpenSSL。源代码被隔离，无法更改。

要链接到 OpenSSL 库的静态版本，我们需要做的就是:

export FIPS_SIG=`find /usr/local/ssl -iname incore`
export CC=`find /usr/local/ssl -iname fipsld`
export FIPSLS_CC=`find /usr/bin -iname gcc`

然后，简单地执行:

$CC $CFLAGS <sources> -o myprogram <openssl libs>

旋转的原因是 OpenSSL 将插入一个额外的源文件 - fips_premain.c - 并使用程序源编译它。 (发生了一些额外的步骤，但 fips_premain.c 的编译是相关步骤)。

但是，当使用g++时，有几个符号是未定义的，因为它们是在安装OpenSSL时用C编译器编译的，而g++在调用时找不到它们:

/tmp/fips_premain-20db15.o: In function `FINGERPRINT_premain()':
/usr/local/ssl/fips-2.0/lib/fips_premain.c:103: undefined reference to `FIPS_text_start()'
/usr/local/ssl/fips-2.0/lib/fips_premain.c:116: undefined reference to `FIPS_incore_fingerprint(unsigned char*, unsigned int)'

如果我添加 --no-demangle 链接器选项，输出如下:

/tmp/fips_premain-be4611.o: In function `_Z19FINGERPRINT_premainv':
/usr/local/ssl/fips-2.0/lib/fips_premain.c:103: undefined reference to `_Z15FIPS_text_startv'
/usr/local/ssl/fips-2.0/lib/fips_premain.c:116: undefined reference to `_Z23FIPS_incore_fingerprintPhj'

以下是 fips_premain.c 中感兴趣的行(第 85 行左右):

extern const void         *FIPS_text_start(),  *FIPS_text_end();
extern const unsigned char FIPS_rodata_start[], FIPS_rodata_end[];
extern unsigned char       FIPS_signature[20];
extern unsigned int        FIPS_incore_fingerprint(unsigned char *,unsigned int);

有没有办法从命令行将符号标记为 extern "C"？

Answer 1

在编译命令行上的文件之前使用 g++ 提供 -x c 开关将强制将其编译为 C 文件而不是默认的 C++。

来自Fipsld and C++页面:

Open fipsld++ and find occurrences where fips_premain.c is compiled. It is compiled through the variable {PREMAIN_C} ...

Change the lines so that -x c preceeds "${PREMAIN_C}", and -x none follows it.

${CC}  ${CANISTER_O_CMD:+"${CANISTER_O_CMD}"} \
    -x c "${PREMAIN_C}" -x none \
    ${_WL_PREMAIN} "$@"

Forcing C compilation on fips_premain.c applies to all configurations (libraries, shared objects, and executables), so you are safe to apply it to all sections of fipsld++.