[Crash-utility] [PATCH] arm64: support compat user mode prstatus

[Dave Anderson]

----- Original Message -----
> On Fri, Dec 18, 2015 at 11:55:07PM +0100, Andrew Jones wrote:
> > compat user mode prstatus already just works, almost. This missing
> > pieces are that pt_regs->sp and pt_regs->fp are not in their usual
> > locations. We need to pull them out of their architecturally mapped
> > general purpose registers.
> > ---
> >  arm64.c | 42 ++++++++++++++++++++++++++++++++++--------
> >  1 file changed, 34 insertions(+), 8 deletions(-)
> > 
> > diff --git a/arm64.c b/arm64.c
> > index 183e768498fe8..3a82d20cdd465 100644
> > --- a/arm64.c
> > +++ b/arm64.c
> > @@ -993,6 +993,25 @@ arm64_stackframe_init(void)
> >  #define PSR_MODE_EL3h   0x0000000d
> >  #define PSR_MODE_MASK   0x0000000f
> >  
> > +/* Architecturally defined mapping between AArch32 and AArch64 registers
> > */
> > +#define compat_usr(x)   regs[(x)]
> > +#define compat_fp       regs[11]
> > +#define compat_sp       regs[13]
> > +#define compat_lr       regs[14]
> > +
> > +#define user_mode(ptregs) \
> > +	(((ptregs)->pstate & PSR_MODE_MASK) == PSR_MODE_EL0t)
> > +
> > +#define compat_user_mode(ptregs)  \
> > +	(((ptregs)->pstate & (PSR_MODE32_BIT | PSR_MODE_MASK)) == \
> > +	 (PSR_MODE32_BIT | PSR_MODE_EL0t))
> > +
> > +#define user_stack_pointer(ptregs) \
> > +	(!compat_user_mode(ptregs) ? (ptregs)->sp : (ptregs)->compat_sp)
> > +
> > +#define user_frame_pointer(ptregs) \
> > +	(!compat_user_mode(ptregs) ? (ptregs)->regs[29] : (ptregs)->compat_fp)
> > +
> >  static int
> >  arm64_is_kernel_exception_frame(struct bt_info *bt, ulong stkptr)
> >  {
> > @@ -1340,21 +1359,28 @@ arm64_get_dumpfile_stackframe(struct bt_info *bt,
> > struct arm64_stackframe *frame
> >  	struct machine_specific *ms = machdep->machspec;
> >  	struct arm64_pt_regs *ptregs;
> >  
> > -	if (!ms->panic_task_regs ||
> > -	    (!ms->panic_task_regs[bt->tc->processor].sp &&
> > -	     !ms->panic_task_regs[bt->tc->processor].pc)) {
> > +	if (!ms->panic_task_regs || !ms->panic_task_regs[bt->tc->processor].pc) {
> 
> Hi Dave,
> 
> I'm having second thoughts about keeping the
> !ms->panic_task_regs[bt->tc->processor].pc test. pc being zero sounds
> like a good reason to crash, or a potential status of a pc after a crash.
> I don't think we should be too hasty to reject the rest of the registers.
> Is there anyway we can relax the sanity checking, but still keep the crash
> utility happy?
> 
> Thanks,
> drew

Hi Drew,

OK, refresh my mind -- I'm not sure what the reasoning behind the patch snippet above?

Originally the code checked whether *both* the sp and pc are NULL, and if so, returns
BT_REGS_NOT_FOUD (which seems fair to me).  Your patch stops checking for a NULL sp, but
still checks for a NULL pc.  In this QEMU dump, the patch doesn't really accomplish anything, 
since both incoming registers are non-NULL (albeit with a sp pointing to 16-bytes below the
top of the stack).  It seems like we could leave it as-is.

Dave
 


> >  		bt->flags |= BT_REGS_NOT_FOUND;
> >  		return FALSE;
> >  	}
> >  
> >  	ptregs = &ms->panic_task_regs[bt->tc->processor];
> > -	frame->sp = ptregs->sp;
> >  	frame->pc = ptregs->pc;
> > -	frame->fp = ptregs->regs[29];
> > -
> > -	if (!is_kernel_text(frame->pc) &&
> > -	    in_user_stack(bt->tc->task, frame->sp))
> > +	if (user_mode(ptregs)) {
> > +		frame->sp = user_stack_pointer(ptregs);
> > +		frame->fp = user_frame_pointer(ptregs);
> > +		if (is_kernel_text(frame->pc) ||
> > +		    !in_user_stack(bt->tc->task, frame->sp)) {
> > +			error(WARNING, "Corrupt prstatus? pstate=0x%lx, but no user frame
> > found\n",
> > +										ptregs->pstate);
> > +			bt->flags |= BT_REGS_NOT_FOUND;
> > +			return FALSE;
> > +		}
> >  		bt->flags |= BT_USER_SPACE;
> > +	} else {
> > +		frame->sp = ptregs->sp;
> > +		frame->fp = ptregs->regs[29];
> > +	}
> >  
> >  	if (arm64_in_kdump_text(bt, frame))
> >  		bt->flags |= BT_KDUMP_ADJUST;
> > --
> > 1.8.3.1
> > 
> > --
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> > Crash-utility at redhat.com
> > https://www.redhat.com/mailman/listinfo/crash-utility
> 
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