Hi Christoph, On 6/24/19 6:43 AM, Christoph Hellwig wrote: > The kernel runs in M-mode without using page tables, and thus can't run > bare metal without help from additional firmware. > > Most of the patch is just stubbing out code not needed without page > tables, but there is an interesting detail in the signals implementation: > > - The normal RISC-V syscall ABI only implements rt_sigreturn as VDSO > entry point, but the ELF VDSO is not supported for nommu Linux. > We instead copy the code to call the syscall onto the stack. > > In addition to enabling the nommu code a new defconfig for a small > kernel image that can run in nommu mode on qemu is also provided, to run > a kernel in qemu you can use the following command line: > > qemu-system-riscv64 -smp 2 -m 64 -machine virt -nographic \ > -kernel arch/riscv/boot/loader \ > -drive file=rootfs.ext2,format=raw,id=hd0 \ > -device virtio-blk-device,drive=hd0 > > Contains contributions from Damien Le Moal <Damien.LeMoal@xxxxxxx>. > > Signed-off-by: Christoph Hellwig <hch@xxxxxx> > --- > arch/riscv/Kconfig | 24 +++++--- > arch/riscv/configs/nommu_virt_defconfig | 78 +++++++++++++++++++++++++ > arch/riscv/include/asm/elf.h | 4 +- > arch/riscv/include/asm/futex.h | 6 ++ > arch/riscv/include/asm/io.h | 4 ++ > arch/riscv/include/asm/mmu.h | 3 + > arch/riscv/include/asm/page.h | 12 +++- > arch/riscv/include/asm/pgalloc.h | 2 + > arch/riscv/include/asm/pgtable.h | 38 ++++++++---- > arch/riscv/include/asm/tlbflush.h | 7 ++- > arch/riscv/include/asm/uaccess.h | 4 ++ > arch/riscv/kernel/Makefile | 3 +- > arch/riscv/kernel/entry.S | 11 ++++ > arch/riscv/kernel/head.S | 6 ++ > arch/riscv/kernel/signal.c | 17 +++++- > arch/riscv/lib/Makefile | 8 +-- > arch/riscv/mm/Makefile | 3 +- > arch/riscv/mm/cacheflush.c | 2 + > arch/riscv/mm/context.c | 2 + > arch/riscv/mm/init.c | 2 + > 20 files changed, 200 insertions(+), 36 deletions(-) > create mode 100644 arch/riscv/configs/nommu_virt_defconfig > snip... > > diff --git a/arch/riscv/configs/nommu_virt_defconfig b/arch/riscv/configs/nommu_virt_defconfig > new file mode 100644 > index 000000000000..cf74e179bf90 > --- /dev/null > +++ b/arch/riscv/configs/nommu_virt_defconfig > @@ -0,0 +1,78 @@ > +# CONFIG_CPU_ISOLATION is not set > +CONFIG_LOG_BUF_SHIFT=16 > +CONFIG_PRINTK_SAFE_LOG_BUF_SHIFT=12 > +CONFIG_BLK_DEV_INITRD=y > +# CONFIG_RD_BZIP2 is not set > +# CONFIG_RD_LZMA is not set > +# CONFIG_RD_XZ is not set > +# CONFIG_RD_LZO is not set > +# CONFIG_RD_LZ4 is not set > +CONFIG_CC_OPTIMIZE_FOR_SIZE=y > +CONFIG_EXPERT=y > +# CONFIG_SYSFS_SYSCALL is not set > +# CONFIG_FHANDLE is not set > +# CONFIG_BASE_FULL is not set > +# CONFIG_EPOLL is not set > +# CONFIG_SIGNALFD is not set > +# CONFIG_TIMERFD is not set > +# CONFIG_EVENTFD is not set > +# CONFIG_AIO is not set > +# CONFIG_IO_URING is not set > +# CONFIG_ADVISE_SYSCALLS is not set > +# CONFIG_MEMBARRIER is not set > +# CONFIG_KALLSYMS is not set > +# CONFIG_VM_EVENT_COUNTERS is not set > +# CONFIG_COMPAT_BRK is not set > +CONFIG_SLOB=y > +# CONFIG_SLAB_MERGE_DEFAULT is not set > +# CONFIG_MMU is not set > +CONFIG_MAXPHYSMEM_2GB=y > +CONFIG_SMP=y > +CONFIG_CMDLINE="root=/dev/vda rw earlycon=uart8250,mmio,0x10000000,115200n8 console=ttyS0" > +CONFIG_CMDLINE_FORCE=y > +# CONFIG_BLK_DEV_BSG is not set > +CONFIG_PARTITION_ADVANCED=y > +# CONFIG_MSDOS_PARTITION is not set > +# CONFIG_EFI_PARTITION is not set > +# CONFIG_MQ_IOSCHED_DEADLINE is not set > +# CONFIG_MQ_IOSCHED_KYBER is not set > +CONFIG_BINFMT_FLAT=y IIUC, RISC-V requires stack pointer to be 16 byte aligned, but flat loader would align stack pointer to max(sizeof(void *), ARCH_SLAB_MINALIGN). So, I think you might want to define ARCH_SLAB_MINALIGN. Cheers Vladimir
