Re: v4.17 regression: PowerMac G3 won't boot, was Re: [PATCH v5 1/3] of: cache phandle nodes to reduce cost of of_find_node_by_phandle()

[The Cc list got pruned so I'm forwarding Stan's reply for the benefit of 
the list archives and any other interested parties.]

On Mon, 10 Sep 2018, Stan Johnson wrote:

On 9/10/18 6:53 AM, Rob Herring wrote:

quoted

...
Can you try this patch (w/o Ben's patch). I think the problem is if 
there are no phandles, then roundup_pow_of_two is passed 0 which is 
documented as undefined result.

Though, if a DT has no properties with phandles, then why are we doing a 
lookup in the first place?


8<----------------------------------------------------------------------

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 9095b8290150..74eaedd5b860 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c

@@ -140,6 +140,9 @@ void of_populate_phandle_cache(void)
 		if (np->phandle && np->phandle != OF_PHANDLE_ILLEGAL)
 			phandles++;
 
+	if (!phandles)
+		goto out;
+
 	cache_entries = roundup_pow_of_two(phandles);
 	phandle_cache_mask = cache_entries - 1;
 

Using the attached .config file, I first compiled the stock 4.18
kernel from kernel.org; it hung at the Mac OS background screen
on my Beige G3 Desktop using the BootX extension and the BootX.app
from within MacOS.  I then applied the above patch, and it booted
without any problems from both the BootX extension and using the
BootX.app from within MacOS.

-Stan