From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.chez-thomas.org (hermes.mlbassoc.com [64.234.241.98]) by mx1.pokylinux.org (Postfix) with ESMTP id 852F84C8005F for ; Thu, 9 Jun 2011 06:32:51 -0500 (CDT) Received: by mail.chez-thomas.org (Postfix, from userid 999) id BE2C21660303; Thu, 9 Jun 2011 05:32:50 -0600 (MDT) X-Spam-Checker-Version: SpamAssassin 3.3.2-r929478 (2010-03-31) on hermes.chez-thomas.org X-Spam-Level: X-Spam-Status: No, score=-2.9 required=4.0 tests=ALL_TRUSTED,BAYES_00 autolearn=unavailable version=3.3.2-r929478 Received: from [127.0.0.1] (localhost.localdomain [127.0.0.1]) by mail.chez-thomas.org (Postfix) with ESMTP id 50DA916602CF; Thu, 9 Jun 2011 05:32:49 -0600 (MDT) Message-ID: <4DF0AF61.1020108@mlbassoc.com> Date: Thu, 09 Jun 2011 05:32:49 -0600 From: Gary Thomas User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.17) Gecko/20110428 Fedora/3.1.10-1.fc15 Thunderbird/3.1.10 MIME-Version: 1.0 To: Khem Raj References: <4DEFB4BA.7050902@mlbassoc.com> <4DEFBD77.7000400@linux.intel.com> <4DF016F0.4080106@gmail.com> <4DF02EDF.5040502@mlbassoc.com> <4DF06CB0.1040501@gmail.com> <4DF0AC87.2060901@mlbassoc.com> In-Reply-To: <4DF0AC87.2060901@mlbassoc.com> Cc: Poky Project Subject: Re: BeagleBoard using GCC 4.6.0 X-BeenThere: poky@yoctoproject.org X-Mailman-Version: 2.1.13 Precedence: list List-Id: Poky build system developer discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 09 Jun 2011 11:32:51 -0000 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit On 06/09/2011 05:20 AM, Gary Thomas wrote: > On 06/09/2011 12:48 AM, Khem Raj wrote: >> On 06/08/2011 07:24 PM, Gary Thomas wrote: >>> On 06/08/2011 06:42 PM, Khem Raj wrote: >>>> On 06/08/2011 11:20 AM, Saul Wold 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 : cmp r3, #0 ; 0x0 >>>>>> 0xc0229814 : beq 0xc0229df8 >>>>>> >>>>>> 0xc0229818 : cmp r3, r0 >>>>>> 0xc022981c : bgt 0xc0229df8 >>>>>> >>>>>> 0xc0229820 : sub r8, r3, #1 ; 0x1 >>>>>> 0xc0229824 : ldr r5, [r7, #4] >>>>>> 0xc0229828 : uxth r8, r8 >>>>>> 0xc022982c : dmb sy >>>>>> >>>>>> With GCC 4.6.0: >>>>>> 0xc0221630 : cmp r3, #0 ; 0x0 >>>>>> 0xc0221634 : beq 0xc0221d7c >>>>>> >>>>>> 0xc0221638 : cmp r3, r0 >>>>>> 0xc022163c : bgt 0xc0221d7c >>>>>> >>>>>> 0xc0221640 : sub r7, r3, #1 ; 0x1 >>>>>> 0xc0221644 : add r3, r11, #16 ; 0x10 >>>>>> 0xc0221648 : add r3, r8, r3, lsl #2 >>>>>> 0xc022164c : uxth r7, r7 >>>>>> 0xc0221650 : ldrb r5, [r3, #5] >>>>>> 0xc0221654 : ldrb r2, [r3, #4] >>>>>> 0xc0221658 : orr r5, r2, r5, lsl #8 >>>>>> 0xc022165c : ldrb r2, [r3, #6] >>>>>> 0xc0221660 : ldrb r3, [r3, #7] >>>>>> 0xc0221664 : orr r5, r5, r2, lsl #16 >>>>>> 0xc0221668 : orr r5, r5, r3, lsl #24 >>>>>> 0xc022166c : 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). >>>>>> >>>>>> Any ideas where I can go with this? I'm really trying to keep up with >>>>>> Poky/Yocto, but this move to GCC 4.6.0 has broken my ARM targets :-( >>>>>> I do have PowerPC targets as well - they seem fine (from limited >>>>>> testing) >>>>>> with the new compiler. >>>>>> >>>>>> Note: if you want to see the whole function disassembly, look at >>>>>> http://www.mlbassoc.com/poky/ehci_hub_control-disassembly-gcc-4.5.2 >>>>>> http://www.mlbassoc.com/poky/ehci_hub_control-disassembly-gcc-4.6.0 >>>>>> >>>>>> Thanks >>>>>> >>>> >>>> OK. thanks for sending the sample code. >>>> Can you add -fstrict-volatile-bitfields option to CFLAGS while >>>> compiling this file or even the kernel for test sake ? >>>> and see if the problem goes away ? >>> >>> Sorry, this doesn't seem to make any difference in the generated code. >>> Hardly surprising as the register in question is a simple u32, not a >>> bitfield. >>> >> >> I reduced the testcase a bit further and it seems the bug is similar to http://gcc.gnu.org/bugzilla/PR45819 >> >> but a bit different that in this case -fstrict-volatile-bitfields does not help >> >> a fix for this particular problem is >> >> diff --git a/include/linux/usb/ehci_def.h b/include/linux/usb/ehci_def.h >> index 6563802..b8c1833 100644 >> --- a/include/linux/usb/ehci_def.h >> +++ b/include/linux/usb/ehci_def.h >> @@ -194,7 +194,7 @@ struct ehci_dbg_port { >> u32 data47; >> u32 address; >> #define DBGP_EPADDR(dev, ep) (((dev)<<8)|(ep)) >> -} __attribute__ ((packed)); >> +} __attribute__ ((packed,aligned(__alignof__(int)))); >> >> #ifdef CONFIG_EARLY_PRINTK_DBGP >> #include >> >> >> since this particular structure all elements are integers but there might be more packed structures which have say char or short ints >> and are not necessarily ordered in the descending order of alignment >> >> Try it out and see if it helps > > Yes, this does fix the problem :-) The EHCI USB port on the OMAP > is working again. Note: it also works properly if the __attribute__ ((packed)) is simply removed. Looking at the layout of this structure, I don't see what that attribute is trying to accomplish - every item within the structure is u32[], so IMO there is nothing to pack. Perhaps this observation can help the GCC folks figure out why things are getting confused. Thanks again -- ------------------------------------------------------------ Gary Thomas | Consulting for the MLB Associates | Embedded world ------------------------------------------------------------