1、编译运行

Makefile等在M3实验中已详细说明，这里不再赘述。

这小节代码完整实现请查看：https://github.com/thomas-coding/baremetal

1.1 代码

先用一行汇编，看下arm系列的编译，elf情况

Vectors:
        b       Reset_Handler
        b       .

        .globl   Reset_Handler
Reset_Handler:
        mov             r0, #1
        mov             r1, #2
        mov             r2, #3
        b               .

MEMORY
{
        FLASH (rwx) : ORIGIN = 0, LENGTH = 0x08000000
}

ENTRY(Reset_Handler)

SECTIONS
{
        .text :
        {
                *(.text*)
        } > FLASH
}

链接脚本，从0地址开始放，只有代码段

Note

makefile链接flag修改为-nostdlib -mcpu=cortex-a15

1.2 qemu命令行

qemu_option+=" -machine virt,secure=on -cpu cortex-a15"
qemu_option+=" -bios ${shell_folder}/output/target.bin"
qemu_option+=" -nographic"

1.3 运行结果

=> 0x0 <Vectors>:       b       0x8 <Reset_Handler>
(gdb) si
0x00000008 in Reset_Handler ()
1: x/i $pc
=> 0x8 <Reset_Handler>: mov     r0, #1
(gdb) si
0x0000000c in Reset_Handler ()
1: x/i $pc
=> 0xc <Reset_Handler+4>:       mov     r1, #2
(gdb) info reg r0
r0             0x1                 1

Note

开头pc在 0x0 地址，然后跳转到0x8 的 Reset_Handler ，给 r0 赋值为1，执行完看赋值成功了。最后会进入循环。

1.4 Memory layout

static const MemMapEntry base_memmap[] = {
        /* Space up to 0x8000000 is reserved for a boot ROM */
        [VIRT_FLASH] =              {          0, 0x08000000 },
        [VIRT_CPUPERIPHS] =         { 0x08000000, 0x00020000 },
        /* GIC distributor and CPU interfaces sit inside the CPU peripheral space */
        [VIRT_GIC_DIST] =           { 0x08000000, 0x00010000 },
        [VIRT_GIC_CPU] =            { 0x08010000, 0x00010000 },
        [VIRT_GIC_V2M] =            { 0x08020000, 0x00001000 },
        [VIRT_GIC_HYP] =            { 0x08030000, 0x00010000 },
        [VIRT_GIC_VCPU] =           { 0x08040000, 0x00010000 },
        /* The space in between here is reserved for GICv3 CPU/vCPU/HYP */
        [VIRT_GIC_ITS] =            { 0x08080000, 0x00020000 },
        /* This redistributor space allows up to 2*64kB*123 CPUs */
        [VIRT_GIC_REDIST] =         { 0x080A0000, 0x00F60000 },
        [VIRT_UART] =               { 0x09000000, 0x00001000 },
        [VIRT_RTC] =                { 0x09010000, 0x00001000 },
        [VIRT_FW_CFG] =             { 0x09020000, 0x00000018 },
        [VIRT_GPIO] =               { 0x09030000, 0x00001000 },
        [VIRT_SECURE_UART] =        { 0x09040000, 0x00001000 },
        [VIRT_SMMU] =               { 0x09050000, 0x00020000 },
        [VIRT_PCDIMM_ACPI] =        { 0x09070000, MEMORY_HOTPLUG_IO_LEN },
        [VIRT_ACPI_GED] =           { 0x09080000, ACPI_GED_EVT_SEL_LEN },
        [VIRT_NVDIMM_ACPI] =        { 0x09090000, NVDIMM_ACPI_IO_LEN},
        [VIRT_PVTIME] =             { 0x090a0000, 0x00010000 },
        [VIRT_SECURE_GPIO] =        { 0x090b0000, 0x00001000 },
        [VIRT_MMIO] =               { 0x0a000000, 0x00000200 },
        /* ...repeating for a total of NUM_VIRTIO_TRANSPORTS, each of that size */
        [VIRT_PLATFORM_BUS] =       { 0x0c000000, 0x02000000 },
        [VIRT_SECURE_MEM] =         { 0x0e000000, 0x01000000 },
        [VIRT_PCIE_MMIO] =          { 0x10000000, 0x2eff0000 },
        [VIRT_PCIE_PIO] =           { 0x3eff0000, 0x00010000 },
        [VIRT_PCIE_ECAM] =          { 0x3f000000, 0x01000000 },
        /* Actual RAM size depends on initial RAM and device memory settings */
        [VIRT_MEM] =                { GiB, LEGACY_RAMLIMIT_BYTES },
};

qemu 代码hw/arm/virt.c，看memory map