On 06/04/18 16:50, Ard Biesheuvel wrote:
> KVM on ARM refuses to decode load/store instructions used to perform
> I/O to emulated devices, and instead relies on the exception syndrome
> information to describe the operand register, access size, etc.
> This is only possible for instructions that have a single input/output
> register (as opposed to ones that increment the offset register, or
> load/store pair instructions, etc). Otherwise, QEMU crashes with the
> following error
>
> error: kvm run failed Function not implemented
> R00=01010101 R01=00000008 R02=00000048 R03=08000820
> R04=00000120 R05=7faaa0e0 R06=7faaa0dc R07=7faaa0e8
> R08=7faaa0ec R09=7faaa088 R10=000000ff R11=00000080
> R12=ff000000 R13=7fccfe08 R14=7faa835f R15=7faa887c
> PSR=800001f3 N--- T svc32
> QEMU: Terminated
>
> and KVM produces a warning such as the following in the kernel log
>
> kvm [17646]: load/store instruction decoding not implemented
>
> GCC with LTO enabled will emit such instructions for Mmio[Read|Write]
> invocations performed in a loop, so we need to disable LTO for the
> IoLib library to ensure that the emitted instructions are suitable for
> emulated I/O under KVM
>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Ard Biesheuvel <ard.biesheu...@linaro.org>
> ---
> ArmVirtPkg/ArmVirtQemu.dsc | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/ArmVirtPkg/ArmVirtQemu.dsc b/ArmVirtPkg/ArmVirtQemu.dsc
> index d74feb709cd1..e6e3d82d6ca9 100644
> --- a/ArmVirtPkg/ArmVirtQemu.dsc
> +++ b/ArmVirtPkg/ArmVirtQemu.dsc
> @@ -414,3 +414,21 @@ [Components.AARCH64]
> <LibraryClasses>
> NULL|ArmVirtPkg/Library/FdtPciPcdProducerLib/FdtPciPcdProducerLib.inf
> }
> +
> +[Components.ARM]
> + MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsic.inf {
> + <BuildOptions>
> + //
> + // KVM on ARM refuses to decode load/store instructions used to perform
> + // I/O to emulated devices, and instead relies on the exception
> syndrome
> + // information to describe the operand register, access size, etc.
> + // This is only possible for instructions that have a single
> input/output
> + // register (as opposed to ones that increment the offset register, or
> + // load/store pair instructions, etc).
> + // GCC with LTO enabled will emit such instructions for
> Mmio[Read|Write]
> + // invocations performed in a loop, so we need to disable LTO for this
> + // library to ensure that the emitted instructions are suitable for
> + // emulated I/O under KVM
> + //
> + GCC:*_GCC5_ARM_CC_FLAGS = -fno-lto
> + }
>
Heh :) See <https://bugzilla.redhat.com/show_bug.cgi?id=1576593>.
- Is there perhaps a finer-grained GCC option for this? (This is a
rhetorical question; I know you must have checked.)
- Is this only with gcc-8?
- Should we do the same for the ArmVirtXen and ArmVirtQemuKernel
platforms? In turn, patch "ArmVirt.dsc.inc" instead? (BTW I have no clue
about Xen's emulation of the instructions at hand.)
In general, I'm fine with the patch. According to [1] [2], this appears
to be the right syntax for the goal.
Thanks!
Laszlo
[1]
https://edk2-docs.gitbooks.io/edk-ii-dsc-specification/content/2_dsc_overview/24_[buildoptions]_section.html#table-8-edk-ii-buildoptions-variable-descriptions
[2]
https://edk2-docs.gitbooks.io/edk-ii-dsc-specification/content/2_dsc_overview/211_[components]_section_processing.html#211-components-section-processing
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