What does autoconf actually run for the AC_CHECK_FUNCS functionality [duplicate]

Question

Say in configure.ac I check for the availability of a C function, like

AC_CHECK_FUNCS( [arc4random] )

And later the configure process is positive on this function:

checking for arc4random... yes

What does the configure process actually run (say on a Linux system)? Does it construct a sample program and tries to compile it?

Answer 1

It generates a test program that declares a function with the same name, then compiles and link it. Change a few characters in the name of the function (to make the test fail) and check config.log, you'll see the source code of the test program when it fails.