On 01/09/2017 10:39 PM, [email protected] wrote: > This makes sens to me. You have set feature mask to 3, which means > support for SSE and FPU. The size for those two features, which is all > the the kernel will enable, is 576 bytes. > The 832 is if you were to also turn on AVX (which is bit 2). Now if you > set feature mask to 7, so that the SSE, FPU and AVX features are enabled > then you should get ebx also reporting 832. >
Oh, wow, I completely misunderstood the help message for that. I thought 0 was the bitmask for FPU (ie, "can't disable"), 1 for SSE, 2 for AVX, so 1 | 2 = 3 would be AVX + SSE + FPU. I see now that this understanding is flawed, and it's actually the raw state-component bitmap value. > Of course, if you're able to perform AVX instructions on AVX state with > the feature mask set to 3 without getting a fault, then something is > going very wrong. > This kernel doesn't even seem to boot at all with -cpu host -enable-kvm (or -cpu IvyBridge), regardless of the configuration. Curiously, with -cpu SandyBridge -enable-kvm, it does boot. It seems to be a qemu bug. It seems to be stuck in some sort of loop handling int_0e (page fault). When I attach gdb, I get this sort of behavior: > <int_0e> mov 0xffffffff80745008,%rsp <int_0e+8> add $0x3e8,%rsp <int_0e+15> push %rcx At the start, rsp is x64KSIRQStack, but after an si $rsp is 0? Another si and it's 0x3e8, and trying to execute the push causes gdb to "wait" until I press Ctrl-c, at which point it's back to the top of int_0e and the stack as reported by bt is unchanged: #0 0xffffffff8071537c in int_0e () #1 0x0000000000000002 in ?? () #2 0xffffffff8071538b in int_0e () followed by some garbage. I expect the "waiting" is gdb not knowing what's happening when qemu makes an interrupt happen. If it's at all useful, here's the kernel under consideration: https://files.octayn.net/sel4-4.0.0-x86_64-pc99 It's 4.0.0 with this config: http://ix.io/1PDr Kofi was able to reproduce this in Qemu, but not on Haswell hardware. Any idea what the issue might be? -- cmr http://octayn.net/ +16038524272
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