Re: Fix incorrect mask for ppc64

[Vladimir 'phcoder' Serbinenko]

Why is swap_bytes right solution? It feels like if anything we just need to remove le_to_cpu32

On Tue, Dec 5, 2017, 13:23 <address@hidden> wrote:

From: Masahiro Matsuya <address@hidden>

The netmask configured in firmware is not respected on ppc64 (big endian).
When 255.255.252.0 is set as netmask in firmware, the following is the value of bootpath string in grub_ieee1275_parse_bootpath().

 /vdevice/address@hidden:speed=auto,duplex=auto,192.168.88.10,,192.168.89.113,192.168.88.1,5,5,255.255.252.0,512

The netmask in this bootpath is no problem, since it's a value specified in firmware. But,
The value of 'subnet_mask.ipv4' was set with 0xfffffc00, and __builtin_ctz (~grub_le_to_cpu32 (subnet_mask.ipv4)) returned 16 (not 22).
As a result, 16 was used for netmask wrongly.

1111 1111 1111 1111 1111 1100 0000 0000 # subnet_mask.ipv4 (=0xfffffc00)
0000 0000 1111 1100 1111 1111 1111 1111 # grub_le_to_cpu32 (subnet_mask.ipv4)
1111 1111 0000 0011 0000 0000 0000 0000 # ~grub_le_to_cpu32 (subnet_mask.ipv4)

And, the count of zero with __builtin_ctz can be 16.
This patch changes it as below.

1111 1111 1111 1111 1111 1100 0000 0000 # subnet_mask.ipv4 (=0xfffffc00)
0000 0000 1111 1100 1111 1111 1111 1111 # grub_le_to_cpu32 (subnet_mask.ipv4)
1111 1111 1111 1111 1111 1100 0000 0000 # grub_swap_bytes32(grub_le_to_cpu32 (subnet_mask.ipv4))
0000 0000 0000 0000 0000 0011 1111 1111 # ~grub_swap_bytes32(grub_le_to_cpu32 (subnet_mask.ipv4))

The count of zero with __builtin_clz can be 22. (clz counts the number of one bits preceding the most significant zero bit)
---
 grub-core/net/drivers/ieee1275/ofnet.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/grub-core/net/drivers/ieee1275/ofnet.c b/grub-core/net/drivers/ieee1275/ofnet.c
index 002446be1..3df75357a 100644
--- a/grub-core/net/drivers/ieee1275/ofnet.c
+++ b/grub-core/net/drivers/ieee1275/ofnet.c
@@ -220,8 +220,7 @@ grub_ieee1275_parse_bootpath (const char *devpath, char *bootpath,
                                  flags);
       inter->vlantag = vlantag;
       grub_net_add_ipv4_local (inter,
-                          __builtin_ctz (~grub_le_to_cpu32 (subnet_mask.ipv4)));
-
+                          __builtin_clz (~grub_swap_bytes32(grub_le_to_cpu32 (subnet_mask.ipv4))));
     }

   if (gateway_addr.ipv4 != 0)
--
2.13.5


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