Hi, I recently got a gcc 7.1 based toolchain, and it seems like it generates unaligned code, specifically in the net_set_ip_header function in my case.
Whenever some packet is sent, this data abort is triggered:
=> setenv ipaddr 10.42.0.1; ping 10.42.0.254
using musb-hdrc, OUT ep1out IN ep1in STATUS ep2in
MAC de:ad:be:ef:00:01
HOST MAC de:ad:be:af:00:00
RNDIS ready
musb-hdrc: peripheral reset irq lost!
high speed config #2: 2 mA, Ethernet Gadget, using RNDIS
USB RNDIS network up!
Using usb_ether device
data abort
pc : [<7ff9db10>] lr : [<7ff9f00c>]
reloc pc : [<4a043b10>] lr : [<4a04500c>]
sp : 7bf37cc8 ip : 00000000 fp : 7ff6236c
r10: 7ffed2b8 r9 : 7bf39ee8 r8 : 7ffed2b8
r7 : 00000001 r6 : 00000000 r5 : 0000002a r4 : 7ffed30e
r3 : 14000045 r2 : 01002a0a r1 : fe002a0a r0 : 7ffed30e
Flags: nZCv IRQs off FIQs off Mode SVC_32
Resetting CPU ...
Running objdump on it gives us this:
4a043b04 <net_set_ip_header>:
/*
* Construct an IP header.
*/
/* IP_HDR_SIZE / 4 (not including UDP) */
ip->ip_hl_v = 0x45;
4a043b04: e59f3074 ldr r3, [pc, #116] ; 4a043b80
<net_set_ip_header+0x7c>
{
4a043b08: e92d4013 push {r0, r1, r4, lr}
4a043b0c: e1a04000 mov r4, r0
ip->ip_hl_v = 0x45;
4a043b10: e5803000 str r3, [r0] <---- Abort
ip->ip_tos = 0;
ip->ip_len = htons(IP_HDR_SIZE);
ip->ip_id = htons(net_ip_id++);
4a043b14: e59f3068 ldr r3, [pc, #104] ; 4a043b84
<net_set_ip_header+0x80>
It seems like r0 is indeed set to an unaligned address (0x7ffed30e)
for some reason.
Using a Linaro 6.3 toolchain works on the same commit with the same
config, so it really seems to be a compiler-related issue.
It generates this code:
4a043ec4 <net_set_ip_header>:
/*
* Construct an IP header.
*/
/* IP_HDR_SIZE / 4 (not including UDP) */
ip->ip_hl_v = 0x45;
4a043ec4: e3a03045 mov r3, #69 ; 0x45
{
4a043ec8: e92d4013 push {r0, r1, r4, lr}
4a043ecc: e1a04000 mov r4, r0
ip->ip_hl_v = 0x45;
4a043ed0: e5c03000 strb r3, [r0]
ip->ip_tos = 0;
ip->ip_len = htons(IP_HDR_SIZE);
4a043ed4: e3a03b05 mov r3, #5120 ; 0x1400
ip->ip_tos = 0;
4a043ed8: e3a00000 mov r0, #0
ip->ip_len = htons(IP_HDR_SIZE);
4a043edc: e1c430b2 strh r3, [r4, #2]
ip->ip_id = htons(net_ip_id++);
4a043ee0: e59f3064 ldr r3, [pc, #100] ; 4a043f4c
<net_set_ip_header+0x88>
And it seems like it's using an strb instruction to avoid the
unaligned access.
As far as I know, we are passing --wno-unaligned-access, so the broken
situation should not arise, and yet it does, so I'm a bit confused,
and not really sure what to do from there.
Thanks!
Maxime
--
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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