Re: [PATCH] m68k: virt: correctly set the initial PC

[Laurent Vivier <laurent@vivier.eu>]

Le 04/05/2021 à 16:13, Philippe Mathieu-Daudé a écrit :
> On 5/4/21 3:18 PM, Laurent Vivier wrote:
>> Set initial PC to the entry of the loaded kernel.
>>
>> This fixes kernel reboot with "-kernel" parameter.
>>
>> Signed-off-by: Laurent Vivier <laurent@vivier.eu>
>> ---
>>  hw/m68k/virt.c | 22 +++++++++++++++++-----
>>  1 file changed, 17 insertions(+), 5 deletions(-)
>>
>> diff --git a/hw/m68k/virt.c b/hw/m68k/virt.c
>> index e9a5d4c69b97..4fb3a7ebf0f2 100644
>> --- a/hw/m68k/virt.c
>> +++ b/hw/m68k/virt.c
>> @@ -88,14 +88,21 @@
>>  #define VIRT_VIRTIO_MMIO_BASE 0xff010000     /* MMIO: 0xff010000 - 0xff01ffff */
>>  #define VIRT_VIRTIO_IRQ_BASE  PIC_IRQ(2, 1)  /* PIC: 2, 3, 4, 5, IRQ: ALL */
>>  
>> +typedef struct {
>> +    M68kCPU *cpu;
>> +    hwaddr initial_pc;
>> +    hwaddr initial_stack;
>> +} ResetInfo;
>> +
>>  static void main_cpu_reset(void *opaque)
>>  {
>> -    M68kCPU *cpu = opaque;
>> +    ResetInfo *reset_info = opaque;
>> +    M68kCPU *cpu = reset_info->cpu;
>>      CPUState *cs = CPU(cpu);
>>  
>>      cpu_reset(cs);
>> -    cpu->env.aregs[7] = ldl_phys(cs->as, 0);
>> -    cpu->env.pc = ldl_phys(cs->as, 4);
>> +    cpu->env.aregs[7] = reset_info->initial_stack;
>> +    cpu->env.pc = reset_info->initial_pc;
>>  }
>>  
>>  static void virt_init(MachineState *machine)
>> @@ -116,6 +123,7 @@ static void virt_init(MachineState *machine)
>>      SysBusDevice *sysbus;
>>      hwaddr io_base;
>>      int i;
>> +    ResetInfo *reset_info;
>>  
>>      if (ram_size > 3399672 * KiB) {
>>          /*
>> @@ -127,9 +135,13 @@ static void virt_init(MachineState *machine)
>>          exit(1);
>>      }
>>  
>> +    reset_info = g_malloc0(sizeof(ResetInfo));
>> +
>>      /* init CPUs */
>>      cpu = M68K_CPU(cpu_create(machine->cpu_type));
>> -    qemu_register_reset(main_cpu_reset, cpu);
>> +
>> +    reset_info->cpu = cpu;
>> +    qemu_register_reset(main_cpu_reset, reset_info);
>>  
>>      /* RAM */
>>      memory_region_add_subregion(get_system_memory(), 0, machine->ram);
>> @@ -209,7 +221,7 @@ static void virt_init(MachineState *machine)
>>              error_report("could not load kernel '%s'", kernel_filename);
>>              exit(1);
>>          }
>> -        stl_phys(cs->as, 4, elf_entry); /* reset initial PC */
>> +        reset_info->initial_pc = elf_entry;
> Missing the stack?
>
>            reset_info->initial_stack = ldl_phys(cs->as, 0);

No, as it's a g_malloc0(), initial_stack is set to 0, so aregs[7] (SP) will be reset to 0 on reboot.
We could also set it to  ram_size if we want something usable, but it's not needed for the kernel
entry point.

Thanks,

Laurent