On Thu, Aug 20, 2015 at 06:22:18PM +0300, Peter Mamonov wrote:
> This patch fixes "Ooops, address error on load or ifetch!",
> caused by "usb" command on MIPS architecture.
>
> To reproduce the problem follow the following steps:
>
> 1. Build barebox for MIPS target with -O0 optimization flag:
>
> diff --git a/Makefile b/Makefile
> index 5a7fd5f..da9a8be 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -301,7 +301,7 @@ CPPFLAGS := -D__KERNEL__ -D__BAREBOX__ $(LINUXINCLUDE) -fno-builtin -ffre
>
> CFLAGS := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
> -Werror-implicit-function-declaration \
> - -fno-strict-aliasing -fno-common -Os -pipe
> + -fno-strict-aliasing -fno-common -O0 -pipe
> AFLAGS := -D__ASSEMBLY__
>
> LDFLAGS_barebox := -Map barebox.map
>
> 2. Plug in a usb flash drive.
>
> 3. Run the "usb" command:
>
> barebox@QEMU DUNA:/ usb -s
> USB: scanning bus for devices...
> &(dev->config.interface[0].ep_desc[0].wMaxPacketSize) = a042732a
> Bus 001 Device 001: ID 0000:0000 EHCI Host Controller
> &(dev->config.interface[0].ep_desc[0].wMaxPacketSize) = a0429f02
> &(dev->config.interface[0].ep_desc[1].wMaxPacketSize) = a0429f0b
>
> Ooops, address error on load or ifetch!
>
> $ 0 : 00000000 00000000 a0429f0b a0429de4
> $ 4 : 00000000 0000000a 00000000 000687e0
> $ 8 : 00000000 00000000 00000000 fa000000
> $12 : 00000001 00000004 00000000 00000000
> $16 : 00000000 00000000 00000000 00000000
> $20 : 00000000 00000000 00000000 00000000
> $24 : 00000000 00000000
> $28 : 00000000 a03ffb40 a03ffb40 a082e9f4
> Hi : 00000000
> Lo : 00000000
> epc : a082ea38
> ra : a082e9f4
> Status: b4000002
> Cause : 00008010
> Config: 88d0c083
>
> ### ERROR ### Please RESET the board ###
>
> The source of the error is the following line of code from the usb_parse_config() function:
>
> le16_to_cpus(&(dev->config.interface[ifno].ep_desc[epno].\
> wMaxPacketSize));
>
> Which tries to load half-word from an un-aligned address 0xa0429f0b stored in v0:
>
> a082ea38: 94420000 lhu v0,0(v0)
>
> 0xa0429f0b is an address of wMaxPacketSize member of a struct usb_endpoint_descriptor at offset 4:
>
> struct usb_endpoint_descriptor {
> __u8 bLength;
> __u8 bDescriptorType;
> __u8 bEndpointAddress;
> __u8 bmAttributes;
> __le16 wMaxPacketSize;
> __u8 bInterval;
> __u8 bRefresh;
> __u8 bSynchAddress;
> } __attribute__ ((packed));
>
> The instances of the usb_endpoint_descriptor are stored in a "ep_desc" array:
>
> struct usb_interface {
> ...
> struct usb_endpoint_descriptor ep_desc[USB_MAXENDPOINTS];
> };
>
> Since the size of the usb_endpoint_descriptor is odd (9 bytes),
> the second element of the ep_desc array is un-aligned,
> as well as it's member wMaxPacketSize:
>
> Bus 001 Device 001: ID 0000:0000 EHCI Host Controller
> &(dev->config.interface[0].ep_desc[0].wMaxPacketSize) = a0429f02
> &(dev->config.interface[0].ep_desc[1].wMaxPacketSize) = a0429f0b
>
> A possible fix to this problem is to make the size of the usb_endpoint_descriptor even.
> ---
> include/usb/ch9.h | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/include/usb/ch9.h b/include/usb/ch9.h
> index ab5d531..5b261e6 100644
> --- a/include/usb/ch9.h
> +++ b/include/usb/ch9.h
> @@ -379,6 +379,7 @@ struct usb_endpoint_descriptor {
> /* use USB_DT_ENDPOINT*_SIZE in bLength, not sizeof. */
> __u8 bRefresh;
> __u8 bSynchAddress;
> + __u8 fill;
> } __attribute__ ((packed));
This doesn't look very nice since we modify a ch9 defined struct just for
the sake of using it in an array somewhere else. We can fix it like
this, but please add a comment why we need this.
Another way to fix this would be to embed struct usb_endpoint_descriptor
in another struct and use that one in an array, like this:
struct usb_endpoint {
struct usb_endpoint_descriptor desc;
};
struct usb_configuration {
...
struct usb_endpoint ep_desc[USB_MAXENDPOINTS];
};
Sascha
--
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