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Date:      Tue, 23 Apr 2002 18:30:58 -0400 (EDT)
From:      Kenneth Culver <culverk@alpha.yumyumyum.org>
To:        Andrew Gallatin <gallatin@cs.duke.edu>
Cc:        freebsd-hackers@freebsd.org, <freebsd-current@freebsd.org>
Subject:   Re: implementing linux mmap2 syscall
Message-ID:  <20020423181748.W31638-100000@alpha.yumyumyum.org>
In-Reply-To: <15557.27747.802212.659760@grasshopper.cs.duke.edu>

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> Kenneth Culver writes:
>  > OK, I found another problem, here it is:
>  >
>  > static void
>  > linux_prepsyscall(struct trapframe *tf, int *args, u_int *code, caddr_t
>  > *params)
>  > {
>  > 	args[0] = tf->tf_ebx;
>  > 	args[1] = tf->tf_ecx;
>  > 	args[2] = tf->tf_edx;
>  > 	args[3] = tf->tf_esi;
>  > 	args[4] = tf->tf_edi;
>  > 	*params = NULL;		/* no copyin */
>  > }
>  >
>  > Basically, linux_mmap2 takes 6 args, and this looks here like only 5 args are
>  > making it in... I checked this because the sixth argument to linux_mmap2() in
>  > truss was showing 0x6, but when I printed out that arg from the kernel, it
>  > was showing 0x0. Am I correct here?
>  >
>  > Ken
>
> Yes.  According to http://john.fremlin.de/linux/asm/, linux used to
> parse only 5 args but now it parses six.  Try adding:
> 	  args[5] = tf->tf_ebp;
>
> Drew
>
>
OK, I THINK I found what calls the actual kernel syscall handler, and
sets it's args first, but I'm not sure:

from linux_locore.s

NON_GPROF_ENTRY(linux_sigcode)
	call	*LINUX_SIGF_HANDLER(%esp)
	leal	LINUX_SIGF_SC(%esp),%ebx	/* linux scp */
	movl	LINUX_SC_GS(%ebx),%gs
	movl	%esp, %ebx			/* pass sigframe */
	push	%eax				/* fake ret addr */
	movl	$LINUX_SYS_linux_sigreturn,%eax	/* linux_sigreturn() */
	int	$0x80				/* enter kernel with args
*/
0:	jmp	0b
	ALIGN_TEXT

I think the stuff above copies the args, and whatnot, but I'm not really
sure where it does this exactly...

It calls LINUX_SIGF_HANDLER, which then calls %esp's sf_handler function.
That is where I draw a blank, I don't know which function this is calling,
and can't find where it's being set. I think this might be what I want to
change though. :-P

Does anyone who actually knows assembly have any ideas?

Ken


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