runtime: SIGILL in amd64 optimized memmove during VMOVDQU on AMD Epyc platform #49063
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VMOVDQU is an AVX instruction and the CPU flags says it has AVX. Why it doesn't work? Do we do CPU feature detection incorrectly or the machine (VM) is lying? |
cherrymui
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NeedsInvestigation
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@cherrymui It really is an AMD Epyc with AVX, I'll try to get access to the VM host though |
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Can you reproduce using regular memory instead of your mmap'd memory? I don't understand how weirdly mapped memory would cause a |
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@randall77 this does work. CONFIG_STRICT_DEVMEM=y CONFIG_IO_STRICT_DEVMEM=y and the mapped memory is from /dev/mem, however, as I said, copying small chunks works and produces the expected data. edit: doing a dd on the memory range does not work, it quits with bad address but does so gracefully. |
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My guess: the BIOS memory controller barfs on a 32-byte wide load. |
What version of Go are you using (
go version)?Does this issue reproduce with the latest release?
yes
What operating system and processor architecture are you using (
go env)?go envOutputWhat did you do?
I am using syscall.Memmap to map 0xFF000000 (iomem where the BIOS is) into userspace and copy it, see the following snippet:
fd, err := os.OpenFile(common.DefaultDevMemPath, os.O_RDWR, 0) if err != nil { return nil, err } defer fd.Close() mem, err := syscall.Mmap(int(fd.Fd()), int64(biosRegionMmap), maxMappedMem, syscall.PROT_READ, syscall.MAP_SHARED) if err != nil { return nil, err } defer syscall.Munmap(mem) r = bytes.NewReader(mem) return io.ReadAll(r)What did you expect to see?
io.ReadAll returning an array.
What did you see instead?
Important Note:
When I deliberately defeat the optimization by copying 256-byte chunks, then the code works. It works on other AMD Zen-based systems, but not this one:
Code is running inside a VM.
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