Re: 转发: Call into a function?

[James E Wilson <wilson at specifixinc dot com>]

Zhenyu Guo wrote:
> gcc --static test.c -o test

Hmm, it turns out that the code really does do that.  This had me
puzzled for a bit until I remembered that a weak function call would
look like this.  This would have been easier if I had the source code to
look at, but I couldn't find gmon_initializer in either gcc or glibc.  I
am not sure where it is coming from.  Maybe I am looking at the wrong
version of the gcc and glibc sources.

Anyways, the input is going to be something like this:
extern void __gmon_start__ (void) __attribute__ ((weak));
void
gmon_initializer (void)
{
  ...
  if (__gmon_start__)
    __gmon_start__ ();
 ...
}

So in a normal link, __gmon_start__ will not be defined, the body of the
if statement will never execute, and the __gmon_start__ call will be
compiled to an offset of 0, which will be a recursive call to itself.

Compile with -pg, and you will see that you now have a call to
__gmon_start__ because it is now defined.

You can also do "objdump -d -r /usr/lib/crti.o" to see the input code
with relocations, and run "nm /usr/lib/crti.o" to see that
__gmon_start__ is weak.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com