Re: what's parisc execve_wrapper doing in the end?

James Bottomley
2012-10-04T10:02:16Z

[cc: parisc list]
On Thu, 2012-10-04 at 06:13 +0100, Al Viro wrote:
> On Thu, Oct 04, 2012 at 05:51:50AM +0100, Al Viro wrote:
> > I'm really confused by that one:
> > /* If exec succeeded we need to load the args */
> >
> > ldo -1024(%r0),%r1
> > cmpb,>>= %r28,%r1,error_\execve
> > copy %r2,%r19
> >
> > error_\execve:
> > bv %r0(%r19)
> >
> > Just what is going on there? That cmpb is non-nullifying, right? So this
> > assignment to %r2 happens whether condition is true or false. And AFAICS
> > IAOQ_Next is set to error_\execve in both cases. So what the hell
> > is that comparison for (and the comment about)? Why not simply return
> > via bv %r0(%r2) and be done with that? It had been done that way since
> > the initial parisc merge circa 2.4.0-test*...
>
> FWIW, I suspect that hpux_execve_wrapper might have something to do with it -
> there we have
> comb,>>= %r28,%r1,exec_error
> copy %r2,%r19
> ldo -TASK_SZ_ALGN-64(%r30),%r1 ;! get task ptr
> LDREG TASK_PT_GR26(%r1),%r26
> LDREG TASK_PT_GR25(%r1),%r25
> LDREG TASK_PT_GR24(%r1),%r24
> LDREG TASK_PT_GR23(%r1),%r23
> copy %r0,%r2 /* Flag to syscall_exit not to clear args */
>
> exec_error:
> instead and that at least makes some sense (even though I don't see
> why syscall_exit would fail to restore them or would check %r2). Is
> the execve_wrapper a rudiment of something similar? It's beyond the
> history observable in the mainline, unfortunately... ;-/

It's plausible. I just verified the theory that the branch is redundant
by successfully booting with this patch applied.

James

---

diff --git a/arch/parisc/kernel/entry.S b/arch/parisc/kernel/entry.S
index 18670a0..d1da93f 100644
--- a/arch/parisc/kernel/entry.S
+++ b/arch/parisc/kernel/entry.S
@@ -1893,15 +1893,7 @@ ENDPROC(sys_vfork_wrapper)

ldo -FRAME_SIZE(%r30),%r30
LDREG -RP_OFFSET(%r30),%r2
-
- /* If exec succeeded we need to load the args */
-
- ldo -1024(%r0),%r1
- cmpb,>>= %r28,%r1,error_\execve
- copy %r2,%r19