LKML Archive on
 help / color / Atom feed
* Linux i386 clone(): %ebx 'frobbing' ?
@ 2008-02-15 18:42 Ahmed S. Darwish
  2008-02-15 20:07 ` Andreas Schwab
  0 siblings, 1 reply; 5+ messages in thread
From: Ahmed S. Darwish @ 2008-02-15 18:42 UTC (permalink / raw)
  To: libc-alpha, libc-alpha; +Cc: linux-kernel

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 */

/* Child */
	/* 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

^ permalink raw reply	[flat|nested] 5+ messages in thread

end of thread, back to index

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2008-02-15 18:42 Linux i386 clone(): %ebx 'frobbing' ? Ahmed S. Darwish
2008-02-15 20:07 ` Andreas Schwab
2008-02-15 23:07   ` Ahmed S. Darwish
2008-02-15 23:28     ` Andreas Schwab
2008-02-15 23:54       ` Ahmed S. Darwish

LKML Archive on

Archives are clonable:
	git clone --mirror lkml/git/0.git
	git clone --mirror lkml/git/1.git
	git clone --mirror lkml/git/2.git
	git clone --mirror lkml/git/3.git
	git clone --mirror lkml/git/4.git
	git clone --mirror lkml/git/5.git
	git clone --mirror lkml/git/6.git
	git clone --mirror lkml/git/7.git
	git clone --mirror lkml/git/8.git
	git clone --mirror lkml/git/9.git
	git clone --mirror lkml/git/10.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ \
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone