Hi all,
In the clone(int (*fn)(void *arg), void *child_stack, ..., void *arg, ...)
Glibc library function defind in sysdeps/unix/sysv/linux/i386/:
`fn' is saved in 8(child_stack), and `arg' is stored in 12(child_stack):
movl STACK(%esp),%ecx
movl ARG(%esp),%eax /* no negative argument counts */
movl %eax,12(%ecx) <---
/* Save the function pointer as the zeroth argument.
It will be popped off in the child in the ebx frobbing below. */
movl FUNC(%esp),%eax
movl %eax,8(%ecx) <---
But after the exectuion of `sys_clone' system call, `fn' is
called in the child thread by the statement 'call *%ebx' as follows:
int $0x80
[...]
test %eax,%eax
jz L(thread_start)
/* Parent */
L(pseudo_end):
ret
/* Child */
L(thread_start):
/* Note: %esi is zero. */
movl %esi,%ebp /* terminate the stack frame */
call *%ebx
I don't understand how the `fn' argument reached the child thread
in the %ebx register. It's said in the comment that `fn' will be
popped to child 'in the ebx frobbing below'. But what does that mean ?
Thanks in advance
--
Ahmed S. Darwish
Homepage: http://darwish.07.googlepages.com
Blog: http://darwish-07.blogspot.com
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