为什么autoconf错误地找到了以后不可用的功能? [英] Why does autoconf erroneously find a function which isn't available later?

问题描述

在Linux系统上，我配置了软件包(llvm)，并且autoconf找到了arc4random函数.这里是配置过程中输出的提取:

On a Linux system I configured a software package (llvm) and autoconf finds the arc4random function. Here an extraction of the output during configuration:

checking for strerror... yes
checking for strerror_r... yes
checking for setenv... yes
checking for arc4random... yes
checking for strtoll... yes
checking for strtoq... yes
checking for sysconf... yes

配置正常.稍后，在构建软件包时，出现关于未声明的说明符arc4random的错误:

Configuring goes fine. Later, when building the package I get an error about an undeclared specifier arc4random:

[removed]/lib/Support/Unix/Process.inc:368:10: error: use of undeclared identifier
      'arc4random'
  return arc4random();
         ^

此处是推荐位置:

367 #if defined(HAVE_ARC4RANDOM)
368   return arc4random();
369 #else
370   static int x = (::srand(GetRandomNumberSeed()), 0);
371   (void)x;
372   return ::rand();
373 #endif

它受到了适当的保护，在这里是configure.ac件:

It's properly guarded, here the configure.ac piece:

AC_CHECK_FUNCS([strerror strerror_r setenv arc4random ])

似乎一切都很好.我想知道为什么配置过程检测到该功能可用.

Seems all fine. I am wondering why the configure process detected the function to be available.

autoconf(GNU Autoconf)2.63

autoconf (GNU Autoconf) 2.63

这里是config.log的摘录:

configure --prefix=[removed] --host=powerpc64-bgq-linux --disable-terminfo --disable-zlib --enable-targets=powerpc CXX=bgclang++ CXXFLAGS=-O3 -fPIC CC=bgclang CFLAGS=-O3 -fPIC LDFLAGS=-shared

推荐答案

根据 arc4random(3) ，要使用此功能，您应该在代码中包含<bsd/stdlib.h>并将其与-lbsd链接.

此AC_CHECK_FUNCS([... arc4random ])的作用是确保系统中存在arc4random，然后定义名为HAVE_ARC4RANDOM的宏，但不能保证您的代码正确使用了它.

What this AC_CHECK_FUNCS([... arc4random ]) does is to make sure arc4random exists in your system, then define the macro named HAVE_ARC4RANDOM, but it cannot guarantee your code is using it correctly.

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