9. Configuration for AArch64 64-bit architecture

This chapter is devoted to the AArch64 64-bit configuration.

Warning

This is a ongoing work… and should be placed in a branch.

9.1. QEMU target

The new platform in the emulated environment is called virt64 (instead of virt32)

The following target is required at the configuration:

cd qemu
./configure --target-list=aarch64-softmmu --disable-attr --disable-docs
make -j8

(The other options may remain unchanged)

9.2. (Virtual) SD-card Storage

The virtual storage file can be generated with the following command:

./create_img.sh virt64

9.3. U-boot

Of course, U-boot must be compiled with the aarch64-linux-gnu toolchain. Edit the Makefile and change the CROSS_COMPILE variable.

U-boot can be configured (and rebuilt) as follows:

make qemu_arm64_defconfig
make -j8

Warning

Since the virtio-blk-device of QEMU has a block size of 512 bytes, the uEnv file stored in uEnv.d directory must not be less than 512 bytes.

9.4. Agency

Warning

Do not forget to modify file build.conf in the agency/ directory in order to have the correct platform.

9.4.1. Linux

Again, the Makefile needs to be adpated accordingly, with the correct CROSS_COMPILE value, i.e. aarch64-linux-gnu Furthermore, the ARCH variable must be set to arm64 (which corresponds to the subdirectory in arm/ directory.

  • The default configuration to be used is virt64_defconfig

9.4.1.1. Address Space Management

Linux address space:

Virtual addresses are 48-bit

  • User space: 0x0000000000000000 - 0x0000800000000000

  • Kernel space: 0xffff800000000000 - 0xffffffffffffffff

Constants:

  • TEXT_OFFSET = 0x800000

  • PHYS_OFFSET = 0x40000000

9.4.1.1.1. Bootstrap

  • The kernel image must have a valid header (used by U-boot) as follows:

struct Image_header {
   uint32_t code0;      /* Executable code */
   uint32_t code1;      /* Executable code */
   uint64_t text_offset;   /* Image load offset, LE */
   uint64_t image_size; /* Effective Image size, LE */
   uint64_t flags;      /* Kernel flags, LE */
   uint64_t res2;    /* reserved */
   uint64_t res3;    /* reserved */
   uint64_t res4;    /* reserved */
   uint32_t magic;      /* Magic number */
   uint32_t res5;
};

The structure above is mapped at the beginning of the image, i.e. the first instructions located at the _head label. code0 and code1 are the location of the two first instructions in head.S (mainly a branch instruction, encoded on 32-bit as any aarch64 instructions).

Possible kernel flags are:

Bit 0: Kernel endianness.  1 if BE, 0 if LE.
Bit 1-2:  Kernel Page size.
      0 - Unspecified.
      1 - 4K
      2 - 16K
      3 - 64K
Bit 3: Kernel physical placement
      0 - 2MB aligned base should be as close as possible
          to the base of DRAM, since memory below it is not
          accessible via the linear mapping
      1 - 2MB aligned base may be anywhere in physical
          memory
Bits 4-63:   Reserved.

Current configuration is: - Kernel Page size unspecified, 2MB aligned base as close as possible to the base of DRAM

  • Start physical address: 0x40000000 (DRAM base for emulated virt machine in QEMU)

9.4.1.1.2. MMU and Page Tables

  • The configuration in Linux is 4 KB page size with 4 levels of translation

  • Each table as 512 entries, hence with 64-bit entries and is stored in a 4 KB page.

  • Bit 63 tells which TTBR0/1 is used (1 -> kernel, 0 -> user space)

9.5. AVZ Hypervisor

  • The hypervisor will be located at 0xffff700000000000

9.6. Realtime Agency

  • The idmap page tables have to be built up during the bootstrap of CPU #1 to enable the MMU since these page tables are not configured by CPU #0 (AVZ already enabled the MMU).

  • A RT task creation must have a stack aligned on 64-byte

  • tpidr_el1 has a reference to the current task_sruct and is used to retrieved the IRQ stack initialized during irq_init()