[poky] BeagleBoard using GCC 4.6.0

[Khem Raj]

On Wed, Jun 8, 2011 at 11:20 AM, Saul Wold <sgw at linux.intel.com> wrote:
> On 06/08/2011 10:43 AM, Gary Thomas wrote:
>>
>> Now that Poky is using GCC 4.6.0, has anyone actually checked the
>> operation on the BeagleBoard? I suspect that you'll find that the
>> EHCI USB does not work. I can't really check here as I don't trust
>> the EHCI on my BeagleBoard rev C3 (not xM).
>>
>> That said, I've tried this new compiler (previously reported) on
>> my own OMAP/3530 board which uses the same 2.6.37 kernel (just not
>> the linux-yocto version). When I build my kernel with GCC 4.5.2,
>> it works perfectly, but fails with GCC 4.6.0 (I trust the hardware).
>>
>> I've isolated it down to at least the function 'ehci_hub_control'
>> (but I suspect the problem is more fundamental). Comparing the code
>> generated by the two compilers with the same source tree, this function
>> is dramatically different. I can see why it's failing, I just don't
>> know why the compiler is doing what it's doing.
>>
>
> Gary,
>
> I am not sure if Khem Raj is on this list, so I am forwarding it to him, he
> might have some insight.
>
> Sau!
>
>
>> The lines at drivers/usb/host/ehci-hub.c:841
>> case GetPortStatus:
>> if (!wIndex || wIndex > ports)
>> goto error;
>> wIndex--;
>> status = 0;
>> temp = ehci_readl(ehci, status_reg);
>>
>> are being compiled very differently.
>>
>> With GCC 4.5.2:
>> 0xc0229810 <ehci_hub_control+672>: cmp r3, #0 ; 0x0
>> 0xc0229814 <ehci_hub_control+676>: beq 0xc0229df8 <ehci_hub_control+2184>
>> 0xc0229818 <ehci_hub_control+680>: cmp r3, r0
>> 0xc022981c <ehci_hub_control+684>: bgt 0xc0229df8 <ehci_hub_control+2184>
>> 0xc0229820 <ehci_hub_control+688>: sub r8, r3, #1 ; 0x1
>> 0xc0229824 <ehci_hub_control+692>: ldr r5, [r7, #4]
>> 0xc0229828 <ehci_hub_control+696>: uxth r8, r8
>> 0xc022982c <ehci_hub_control+700>: dmb sy
>>
>> With GCC 4.6.0:
>> 0xc0221630 <ehci_hub_control+808>: cmp r3, #0 ; 0x0
>> 0xc0221634 <ehci_hub_control+812>: beq 0xc0221d7c <ehci_hub_control+2676>
>> 0xc0221638 <ehci_hub_control+816>: cmp r3, r0
>> 0xc022163c <ehci_hub_control+820>: bgt 0xc0221d7c <ehci_hub_control+2676>
>> 0xc0221640 <ehci_hub_control+824>: sub r7, r3, #1 ; 0x1
>> 0xc0221644 <ehci_hub_control+828>: add r3, r11, #16 ; 0x10
>> 0xc0221648 <ehci_hub_control+832>: add r3, r8, r3, lsl #2
>> 0xc022164c <ehci_hub_control+836>: uxth r7, r7
>> 0xc0221650 <ehci_hub_control+840>: ldrb r5, [r3, #5]
>> 0xc0221654 <ehci_hub_control+844>: ldrb r2, [r3, #4]
>> 0xc0221658 <ehci_hub_control+848>: orr r5, r2, r5, lsl #8
>> 0xc022165c <ehci_hub_control+852>: ldrb r2, [r3, #6]
>> 0xc0221660 <ehci_hub_control+856>: ldrb r3, [r3, #7]
>> 0xc0221664 <ehci_hub_control+860>: orr r5, r5, r2, lsl #16
>> 0xc0221668 <ehci_hub_control+864>: orr r5, r5, r3, lsl #24
>> 0xc022166c <ehci_hub_control+868>: dmb sy
>>
>> As you can see, the old compiler accesses the ehci status register
>> in a single access, the new compiler dances around and makes multiple
>> accesses, which in the end get very incorrect data (I think that this
>> register is like many which clear bits on reads).

ok seems like unaligned loads are kicking in may be its missing
some qualifier. Can you do me a  favour ? Please send me preprocessed
output of the source file and let me see what I find

-Khem