Re: [PATCH 1/3] target/arm: Use CONFIG_SEMIHOSTING instead of TCG for semihosting

[Alex Bennée]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 5/3/23 21:38, Fabiano Rosas wrote:
>> When building --without-default-devices, the semihosting code will not
>> be available, so check the proper config.
>
> Acked-by: Paolo Bonzini <pbonzini@redhat.com>
>
> for this change; however, there are two more related issues:
>
> 1) you still want to leave out the code if !TCG, because KVM is not able
> to exit to userspace on semihosting calls as far as I understand

Correct.

> 2) I am not sure why CONFIG_ARM_COMPATIBLE_SEMIHOSTING=y appears in
> config/targets/{arm,riscv32,riscv64}-softmmu/default.mak.

I think we need to be clearer in the development guide when things are
triggered by config/devices/ and when they are triggered by default
rules in Kconfig.

After Fabino's series the delta between
config/aarch64-softmmu/minimal.mk and config/aarch64-softmmu/default.mk
is pretty small.

I guess minimal.mk should be renamed to virt.mk, sbsa-ref dropped from
it (as you can't run it under KVM) and what controls which devices the
virt platform can use?

Should it be:

CONFIG_PCI_DEVICES=y
CONFIG_VIRTIO_PCI=y

to ensure we can plug and play all the various VirtIO bits we need for
the KVM/Xen use case?

>
> Putting things together you also need something like
>
> diff --git a/semihosting/Kconfig b/semihosting/Kconfig
> index eaf3a20ef5b2..671020a33426 100644
> --- a/semihosting/Kconfig
> +++ b/semihosting/Kconfig
> @@ -4,4 +4,5 @@ config SEMIHOSTING
>    config ARM_COMPATIBLE_SEMIHOSTING
>         bool
> +       default y if (ARM && TCG) || RISCV32 || RISCV64
>         select SEMIHOSTING
> diff --git a/configs/devices/arm-softmmu/default.mak 
> b/configs/devices/arm-softmmu/default.mak
> index 1b49a7830c7e..5e7a17d05bf8 100644
> --- a/configs/devices/arm-softmmu/default.mak
> +++ b/configs/devices/arm-softmmu/default.mak
> @@ -41,5 +41,4 @@ CONFIG_FSL_IMX25=y
>  CONFIG_FSL_IMX7=y
>  CONFIG_FSL_IMX6UL=y
>  CONFIG_SEMIHOSTING=y
> -CONFIG_ARM_COMPATIBLE_SEMIHOSTING=y
>  CONFIG_ALLWINNER_H3=y
> diff --git a/configs/devices/riscv32-softmmu/default.mak 
> b/configs/devices/riscv32-softmmu/default.mak
> index d847bd5692ec..94a236c9c25b 100644
> --- a/configs/devices/riscv32-softmmu/default.mak
> +++ b/configs/devices/riscv32-softmmu/default.mak
> @@ -3,8 +3,6 @@
>  # Uncomment the following lines to disable these optional devices:
>  #
>  #CONFIG_PCI_DEVICES=n
> -CONFIG_SEMIHOSTING=y
> -CONFIG_ARM_COMPATIBLE_SEMIHOSTING=y
>    # Boards:
>  #
> diff --git a/configs/devices/riscv64-softmmu/default.mak 
> b/configs/devices/riscv64-softmmu/default.mak
> index bc69301fa4a6..3f6805944849 100644
> --- a/configs/devices/riscv64-softmmu/default.mak
> +++ b/configs/devices/riscv64-softmmu/default.mak
> @@ -3,8 +3,6 @@
>  # Uncomment the following lines to disable these optional devices:
>  #
>  #CONFIG_PCI_DEVICES=n
> -CONFIG_SEMIHOSTING=y
> -CONFIG_ARM_COMPATIBLE_SEMIHOSTING=y
>    # Boards:
>  #
>
> Paolo
>
>> Fixes: 29d9efca16 ("arm/Kconfig: Do not build TCG-only boards on a KVM-only 
>> build")
>> Signed-off-by: Fabiano Rosas<farosas@suse.de>
>> ---
>>   target/arm/helper.c       | 4 ++--
>>   target/arm/tcg/m_helper.c | 2 +-
>>   2 files changed, 3 insertions(+), 3 deletions(-)


-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro