[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 02/34] xen: clang: Disable built-in assembler
On 04/01/2014 04:28 PM, Ian Campbell wrote: > On Tue, 2014-04-01 at 15:50 +0100, Julien Grall wrote: >> On 04/01/2014 02:11 PM, Ian Campbell wrote: >>> On Sat, 2014-03-29 at 22:55 +0000, Julien Grall wrote: >>>> Hi Tim, >>>> >>>> On 27/03/14 18:01, Tim Deegan wrote: >>>>> >>>>> The patch below works for me (at least as far as building >>>>> asm-offsets.h on x86) by wrapping everything in a string. I did try >>>>> just prefixing with '#' but clang 3.5 also strips the comments out. >>>>> That seems unhelpful, since I know some people put comments in their >>>>> inline assembler too. :( >>>> >>>> I'm able to build correctly x86 with your patch, and this patch (e.g #2) >>>> reverted. >>>> >>>> But for ARM ... it breaks in another place :( >>>> >>>> vfp.c:8:25: error: invalid operand for instruction >>>> v->arch.vfp.fpexc = READ_CP32(FPEXC); >>>> <inline asm>:1:6: note: instantiated into assembly here >>>> mrc p10, 7, r1, c8, c0, 0; >>>> ^ >>>> >>>> Coprocessor p10 (and p11) are used for Neon instruction are clang >>>> doesn't allow to use it directly. >>>> (http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20131104/194170.html). >>>> >>>> Depends on which part of the ARM ARM you are reading, p10 and p11 should >>>> not be used directly with mrc/mcr instruction ... but gas accept it. >>>> >>>> I guess the best solution is to use directly the VFP instructions but it >>>> would mean to re-enable VFP at compile time in Xen (see >>>> http://www.gossamer-threads.com/lists/xen/devel/284653?do=post_view_threaded). >>> >>> Do the VFP instructions have different encodings? I thought this was an >>> assembler mnemonic difference only. >> >> Strictly speaking it works only because vldm* as the same encoding as >> ldc*. But the processor will decode the instruction as vldm* (and >> execute as it is). > > Are those the instructions in question though? The thing you quoted was > about reading FPEXC which is an mrc cp instruction vs vmrs I think. They > do indeed have identical encodings, so I'm not entirely sure what the > big deal is about which assembler mnemonic gets used is, the process has > no idea what we wrote in the source. Oh sorry, I took one in random. Every VFP instructions has the same issue. I will raise the bug to Clang. And see if why they choose this solution. -- Julien Grall _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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