How to repropduce the unaligned store problem
qemu-system-mips -nodefaults -M malta -m 256 \
-nographic -serial stdio -monitor null \
-bios barebox-flash-image \
-net user -net nic,model=rtl8139
...
barebox:/ dhcp
Ooops, address error on store!
$ 0 : 00000000 00000000 01010600 697f2a2e
$ 4 : a0850000 00000000 0000001c a040c1b8
$ 8 : 00000000 00000002 00000002 00000000
$12 : 00000000 00000040 00000100 00000001
$16 : a040bba0 a0850000 a0850000 a0850000
$20 : 00000000 00000075 00000076 a040ba20
$24 : 00000002 a080f210
$28 : 00000000 a03ffce0 fffffffd a0833b8c
Hi : 000154f8
Lo : 20000000
epc : a0833b84
ra : a0833b8c
Status: 00000002
Cause : 80000414
Config: 80008482
### ERROR ### Please RESET the board ###
The unaligned store instruction is located in the bootp_request() from net/dhcp.c:
a0833b50 <bootp_request>:
..
a0833b7c: 3c020101 lui v0,0x101
a0833b80: 24420600 addiu v0,v0,1536 /* 0x1010600 -> v0 */
a0833b84: 0c20024a jal a0800928 <get_time_ns>
a0833b88: ae02002a sw v0,42(s0) /* store 0x1010600 to addr s0 + 42 */
This assembler code is generated by mips-linux-gnu-gcc (Debian 7.2.0-11) 7.2.0
from this:
bp = (struct bootp *)payload;
bp->bp_op = OP_BOOTREQUEST; /* 0x01 */
bp->bp_htype = HWT_ETHER; /* 0x01 */
bp->bp_hlen = HWL_ETHER; /* 0x06 */
bp->bp_hops = 0;
Compiler replaces four 'store byte' instruction by one 'store 32-bit word'
instruction. Alas sometimes this leads to unaligned store situation.
Making struct bootp __packed prevents this optimization and fixes the problem.
Signed-off-by: Antony Pavlov <antonynpavlov@xxxxxxxxx>
---
net/dhcp.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/dhcp.c b/net/dhcp.c
index c5386fe942..4177220410 100644
--- a/net/dhcp.c
+++ b/net/dhcp.c
@@ -45,7 +45,7 @@ struct bootp {
char bp_sname[64]; /* Server host name */
char bp_file[128]; /* Boot file name */
char bp_vend[0]; /* Vendor information */
-};
+} __packed;
/* DHCP States */
typedef enum {
--
2.15.0
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