Re: [PATCH v3 4/5] xen: Add files needed for minimal riscv build

[Connor Davis <connojdavis@xxxxxxxxx>]

On 5/17/21 5:51 AM, Jan Beulich wrote:
> On 14.05.2021 20:53, Connor Davis wrote:
> > --- /dev/null
> > +++ b/config/riscv64.mk
> > @@ -0,0 +1,5 @@
> > +CONFIG_RISCV := y
> > +CONFIG_RISCV_64 := y
> > +CONFIG_RISCV_$(XEN_OS) := y
> I wonder whether the last one actually gets used anywhere, but I do
> realize that other architectures have similar definitions.
>
> > --- a/xen/Makefile
> > +++ b/xen/Makefile
> > @@ -26,7 +26,9 @@ MAKEFLAGS += -rR
> >   EFI_MOUNTPOINT ?= $(BOOT_DIR)/efi
> >   
> >   ARCH=$(XEN_TARGET_ARCH)
> > -SRCARCH=$(shell echo $(ARCH) | sed -e 's/x86.*/x86/' -e 
> > s'/arm\(32\|64\)/arm/g')
> > +SRCARCH=$(shell echo $(ARCH) | \
> > +         sed -e 's/x86.*/x86/' -e s'/arm\(32\|64\)/arm/g' \
> > +             -e s'/riscv.*/riscv/g')
> I think in makefiles tab indentation would better be restricted to
> rules. While here it's a minor nit, ...
>
> > @@ -35,7 +37,8 @@ include $(XEN_ROOT)/Config.mk
> >   # Set ARCH/SUBARCH appropriately.
> >   export TARGET_SUBARCH  := $(XEN_TARGET_ARCH)
> >   export TARGET_ARCH     := $(shell echo $(XEN_TARGET_ARCH) | \
> > -                            sed -e 's/x86.*/x86/' -e s'/arm\(32\|64\)/arm/g')
> > +                            sed -e 's/x86.*/x86/' -e s'/arm\(32\|64\)/arm/g' \
> > +                               -e s'/riscv.*/riscv/g')
> ... here you're actually introducing locally inconsistent indentation.
>
> > --- /dev/null
> > +++ b/xen/arch/riscv/Kconfig
> > @@ -0,0 +1,52 @@
> > +config 64BIT
> > +       bool
> I'm afraid this is stale now - the option now lives in xen/arch/Kconfig,
> available to all architectures.
>
> > +config RISCV_64
> > +       bool
> > +       depends on 64BIT
> Such a "depends on" is relatively pointless - they're more important to
> have when there is a prompt.
>
> > +config ARCH_DEFCONFIG
> > +       string
> > +       default "arch/riscv/configs/riscv64_defconfig" if RISCV_64
> For the RISCV_64 dependency to be really useful (at least with the
> command line kconfig), you want its selection to live above the use.
>
> > +menu "Architecture Features"
> > +
> > +source "arch/Kconfig"
> > +
> > +endmenu
> > +
> > +menu "ISA Selection"
> > +
> > +choice
> > +       prompt "Base ISA"
> > +        default RISCV_ISA_RV64IMA
> > +        help
> > +          This selects the base ISA extensions that Xen will target.
> > +
> > +config RISCV_ISA_RV64IMA
> > +       bool "RV64IMA"
> > +        select 64BIT
> > +        select RISCV_64
> I think you want only the latter here, and the former done by RISCV_64
> (or select the former here, and have "default y if 64BIT" at RISCV_64).
> That way, not every party wanting 64-bit has to select both.
>
> > +        help
> > +           Use the RV64I base ISA, plus the "M" and "A" extensions
> > +           for integer multiply/divide and atomic instructions, respectively.
> > +
> > +endchoice
> > +
> > +config RISCV_ISA_C
> > +       bool "Compressed extension"
> > +        help
> > +           Add "C" to the ISA subsets that the toolchain is allowed
> > +           to emit when building Xen, which results in compressed
> > +           instructions in the Xen binary.
> > +
> > +           If unsure, say N.
> For all of the above, please adjust indentation to be consistent with
> (the bulk of) what we have elsewhere.
Will do
> > --- /dev/null
> > +++ b/xen/arch/riscv/arch.mk
> > @@ -0,0 +1,16 @@
> > +########################################
> > +# RISCV-specific definitions
> > +
> > +ifeq ($(CONFIG_RISCV_64),y)
> > +    CFLAGS += -mabi=lp64
> > +endif
> Wherever possible I think we should prefer the list approach:
>
> CFLAGS-$(CONFIG_RISCV_64) += -mabi=lp64
>
> > --- /dev/null
> > +++ b/xen/arch/riscv/configs/riscv64_defconfig
> > @@ -0,0 +1,12 @@
> > +# CONFIG_SCHED_CREDIT is not set
> > +# CONFIG_SCHED_RTDS is not set
> > +# CONFIG_SCHED_NULL is not set
> > +# CONFIG_SCHED_ARINC653 is not set
> > +# CONFIG_TRACEBUFFER is not set
> > +# CONFIG_DEBUG is not set
> > +# CONFIG_DEBUG_INFO is not set
> > +# CONFIG_HYPFS is not set
> > +# CONFIG_GRANT_TABLE is not set
> > +# CONFIG_SPECULATIVE_HARDEN_ARRAY is not set
> > +
> > +CONFIG_EXPERT=y
> These are rather odd defaults, more like for a special purpose
> config than a general purpose one. None of what you turn off here
> will guarantee to be off for people actually trying to build
> things, so it's not clear to me what the idea here is. As a
> specific remark, especially during bringup work I think it is
> quite important to not default DEBUG to off: You definitely want
> to see whether any assertions trigger.
The idea was to turn off as much stuff as possible to get a minimal
build (involving xen/common) working. Although now that we're focused on
only a few files at a time, they could be enabled without adding any
undue burden (at least for now).

Perhaps it would be best to rename the file to include "tiny" or something,
and then add a normal defconfig once things are actually running?

At any rate, agreed on the DEBUG setting, I will enable that.
> > --- /dev/null
> > +++ b/xen/include/asm-riscv/config.h
> > @@ -0,0 +1,110 @@
> > +/******************************************************************************
> > + * config.h
> > + *
> > + * A Linux-style configuration list.
> May I suggest to not further replicate this now inapplicable
> comment? It was already somewhat bogus for Arm to clone from x86.
Sure thing.
> > + */
> > +
> > +#ifndef __RISCV_CONFIG_H__
> > +#define __RISCV_CONFIG_H__
> > +
> > +#if defined(CONFIG_RISCV_64)
> > +# define LONG_BYTEORDER 3
> > +# define ELFSIZE 64
> > +#else
> > +# error "Unsupported RISCV variant"
> > +#endif
> > +
> > +#define BYTES_PER_LONG (1 << LONG_BYTEORDER)
> > +#define BITS_PER_LONG  (BYTES_PER_LONG << 3)
> > +#define POINTER_ALIGN  BYTES_PER_LONG
> > +
> > +#define BITS_PER_LLONG 64
> > +
> > +/* xen_ulong_t is always 64 bits */
> > +#define BITS_PER_XEN_ULONG 64
> > +
> > +#define CONFIG_RISCV 1
> This duplicates a "real" Kconfig setting, doesn't it?
Yes, will remove, thanks
> > +#define CONFIG_RISCV_L1_CACHE_SHIFT 6
> > +
> > +#define CONFIG_PAGEALLOC_MAX_ORDER 18
> > +#define CONFIG_DOMU_MAX_ORDER      9
> > +#define CONFIG_HWDOM_MAX_ORDER     10
> > +
> > +#define OPT_CONSOLE_STR "dtuart"
> > +
> > +#ifdef CONFIG_RISCV_64
> > +#define MAX_VIRT_CPUS 128u
> > +#else
> > +#error "Unsupported RISCV variant"
> > +#endif
> Could this be folded with the other similar construct further up?
Yep, will do.

Thanks,
Connor