On Thu, Jan 31, 2008 at 06:31:09PM +0100, Alexander Graf wrote:
>
> On Jan 31, 2008, at 10:58 AM, Kevin Wolf wrote:
>
>> Hi,
>>
>> I like this idea. When I just tried to load my multiboot kernel it
>> failed, though, because of the following piece of code:
>>
>>> + // XXX: multiboot header may be within the first 8192 bytes,
>>> but header
>>> + // is only the first 1024
>>> +
>>> + // Ok, let's see if it is a multiboot image
>>> + for(i=0; i<(256 - 12); i+=4) { // the header is 12x32bit long
>>> + if(ldl_p(header+i) == 0x1BADB002) {
>>
>> I wonder if there is any reason why you didn't just replace the 1024
>> by
>> 8192 in load_linux but added an XXX. Would this cause any problems I
>> missed? With this change and replacing 256 by 8192 in the above code
>> it
>> works for my kernel, too.
>>
>> Anyway, I think the for condition should be i < 4 * (256 - 12), even
>> without changing the 1024.
>
> This version should fix the long header issue. I made the linux loader
> fetch the first 8kb as header, so multiboot can search through all
> necessary data.
>
> I also implemented module parameters. Kevin needed this to boot a
> homebrew kernel. You can now pass commandline parameters to the
> multiboot modules by adding them after the filename, seperated through a
> space. This is the very same approach grub takes.
>
> To boot a xen kernel you would give a command line like this:
>
> qemu -hda image -kernel xen -initrd "vmlinux-xen root=/dev/hda,initrd-
> xen"
>
> This way the vmlinux module gets the command line parameter "root=/dev/
> hda".
>
>
> diff --git a/elf_ops.h b/elf_ops.h
> index 6126565..ab5fd7b 100644
> --- a/elf_ops.h
> +++ b/elf_ops.h
> @@ -156,6 +156,10 @@ static int glue(load_elf, SZ)(int fd, int64_t
> virt_to_phys_addend,
> }
>
> if (ELF_MACHINE != ehdr.e_machine)
> +#if (ELF_MACHINE == EM_X86_64) && !CONFIG_USER_ONLY
> + /* x86_64 systems can run i386 code as well */
> + if(ehdr.e_machine != EM_386)
> +#endif
> goto fail;
>
> if (pentry)
> diff --git a/hw/pc.c b/hw/pc.c
> index b4f0db7..4c5ee94 100644
> --- a/hw/pc.c
> +++ b/hw/pc.c
> @@ -480,6 +480,416 @@ static long get_file_size(FILE *f)
> return size;
> }
>
> +/* Generate an initial boot sector which sets state and jump to
> + a specified vector */
> +static void generate_bootsect_multiboot(uint32_t mh_entry_addr, uint32_t
> bootinfo)
> +{
> + uint8_t bootsect[512], *p, *pgdt, *pmmaploop;
> + uint32_t ip;
> + int i;
> + int hda;
> + int mmaploop;
> +
> + hda = drive_get_index(IF_IDE, 0, 0);
> + if (hda == -1) {
> + fprintf(stderr, "A disk image must be given for 'hda' when booting "
> + "a Multiboot kernel\n");
> + exit(1);
> + }
> +
> + memset(bootsect, 0, sizeof(bootsect));
> +
> + /* Copy the MSDOS partition table if possible */
> + bdrv_read(drives_table[hda].bdrv, 0, bootsect, 1);
> +
> + /* Make sure we have a partition signature */
> + bootsect[510] = 0x55;
> + bootsect[511] = 0xaa;
> +
> + /* Actual code */
> + p = bootsect;
> + *p++ = 0xfa; /* CLI */
> + *p++ = 0xfc; /* CLD */
> +
> + // 660f011528000000 lgdt [0x28]
> + *p++ = 0x66; /* 32-bit operand size */
> + *p++ = 0x67; /* 32-bit addr size */
> + *p++ = 0x0f; /* LGDT [0x128] */
> + *p++ = 0x01;
> + *p++ = 0x15;
> + pgdt=p; /* we calculate the gdt position later */
> + p+=4;
> +
> + /* Initialize multiboot mmap structs using the 0x15(e820) */
> + *p++ = 0x31; /* XOR BX,BX */
> + *p++ = 0xdb;
> +
> + *p++ = 0x66; /* 32-bit operand size */
> + *p++ = 0x67; /* 32-bit addr size */
> + *p++ = 0xbf; /* MOV EDI,0x9004 */
> + *p++ = 0x04;
> + *p++ = 0x90;
> + *p++ = 0x00;
> + *p++ = 0x00;
> +
> + pmmaploop = p;
> + *p++ = 0x66; /* 32-bit operand size */
> + *p++ = 0x67; /* 32-bit addr size */
> + *p++ = 0xb8; /* MOV EAX,0x20 */
> + *p++ = 0x20;
> + *p++ = 0x00;
> + *p++ = 0x00;
> + *p++ = 0x00;
> +
> + *p++ = 0x66; /* 32-bit operand size */
> + *p++ = 0x67; /* 32-bit addr size */
> + *p++ = 0x89; /* MOV -4(EDI),EAX */
> + *p++ = 0x47;
> + *p++ = 0xfc;
> +
> + *p++ = 0x66; /* 32-bit operand size */
> + *p++ = 0x67; /* 32-bit addr size */
> + *p++ = 0xb8; /* MOV EAX,0x0000e820 */
> + *p++ = 0x20;
> + *p++ = 0xe8;
> + *p++ = 0x00;
> + *p++ = 0x00;
> +
> + *p++ = 0x66; /* 32-bit operand size */
> + *p++ = 0x67; /* 32-bit addr size */
> + *p++ = 0xba; /* MOV EDX,0x534d4150 */
> + *p++ = 0x50;
> + *p++ = 0x41;
> + *p++ = 0x4d;
> + *p++ = 0x53;
> +
> + *p++ = 0x66; /* 32-bit operand size */
> + *p++ = 0x67; /* 32-bit addr size */
> + *p++ = 0xb9; /* MOV ECX,0x20 */
> + *p++ = 0x20;
> + *p++ = 0x00;
> + *p++ = 0x00;
> + *p++ = 0x00;
> +
> + *p++ = 0xcd; /* INT 0x15 */
> + *p++ = 0x15;
> +
> + *p++ = 0x66; /* 32-bit operand size */
> + *p++ = 0x67; /* 32-bit addr size */
> + *p++ = 0xb8; /* MOV EAX, 0x24 */
> + *p++ = 0x24;
> + *p++ = 0x00;
> + *p++ = 0x00;
> + *p++ = 0x00;
> +
> + *p++ = 0xf7; /* MUL AX, BX */
> + *p++ = 0xe3;
> +
> + *p++ = 0x66; /* 32-bit operand size */
> + *p++ = 0x67; /* 32-bit addr size */
> + *p++ = 0x21; /* AND EBX, EBX */
> + *p++ = 0xdb;
> +
> + /* don't store if bx = 0 */
> + *p++ = 0x66; /* 32-bit operand size */
> + *p++ = 0x67; /* 32-bit addr size */
> + *p++ = 0x0f; /* JZ next instruction */
> + *p++ = 0x84;
> + *p++ = 0x07;
> + *p++ = 0x00;
> + *p++ = 0x00;
> + *p++ = 0x00;
> +
> + /* store the amount of blocks in the bootinfo struct */
> + *p++ = 0x66; /* 32-bit operand size */
> + *p++ = 0x67; /* 32-bit addr size */
> + *p++ = 0xa3; /* MOV [bootinfo+0x2c], EAX */
> + *p++ = (bootinfo+0x2c);
> + *p++ = (bootinfo+0x2c) >> 8;
> + *p++ = (bootinfo+0x2c) >> 16;
> + *p++ = (bootinfo+0x2c) >> 24;
> +
> + *p++ = 0x66; /* 32-bit operand size */
> + *p++ = 0x67; /* 32-bit addr size */
> + *p++ = 0x05; /* ADD EAX, 0x9004 */
> + *p++ = 0x04;
> + *p++ = 0x90;
> + *p++ = 0x00;
> + *p++ = 0x00;
> +
> + *p++ = 0x89; /* MOV DI, AX */
> + *p++ = 0xc7;
> +
> + *p++ = 0x66; /* 32-bit operand size */
> + *p++ = 0x67; /* 32-bit addr size */
> + *p++ = 0x21; /* AND EBX, EBX */
> + *p++ = 0xdb;
> +
> + /* process next entry */
> + *p++ = 0x66; /* 32-bit operand size */
> + *p++ = 0x67; /* 32-bit addr size */
> + *p++ = 0x0f; /* JNZ mmaploop */
> + *p++ = 0x85;
> + mmaploop = (int)((long)pmmaploop) - ((long)p) - 4;
> + *p++ = mmaploop;
> + *p++ = mmaploop >> 8;
> + *p++ = mmaploop >> 16;
> + *p++ = mmaploop >> 24;
> +
> + /* get us to protected mode now */
> +
> + *p++ = 0x66;
> + *p++ = 0xb8; /* MOV EAX,0x01 */
> + *p++ = 0x01;
> + *p++ = 0x00;
> + *p++ = 0x00;
> + *p++ = 0x00;
> +
> + *p++ = 0x0f; /* MOV CR0,EAX */
> + *p++ = 0x22;
> + *p++ = 0xc0;
> +
> + /* the JMP sets CS for us and gets us to 32-bit */
> + ip = 0x00007c00 + (p - bootsect) + 8; // set i to the IP after the JMP
> + *p++ = 0x66; /* 32-bit operand size */
> + *p++ = 0xea; /* JMP */
> + *p++ = ip; /* IP */
> + *p++ = ip >> 8;
> + *p++ = ip >> 16;
> + *p++ = ip >> 24;
> + *p++ = 0x08;
> + *p++ = 0x00;
> +
> + /* initialize all other segments */
> + *p++ = 0xb8; /* MOV EAX,0x10 */
> + *p++ = 0x10;
> + *p++ = 0x00;
> + *p++ = 0x00;
> + *p++ = 0x00;
> + for (i = 0; i < 6; i++) {
> + if (i == 1) /* Skip CS */
> + continue;
> +
> + *p++ = 0x8e; /* MOV <seg>,EAX */
> + *p++ = 0xc0 + (i << 3);
> + }
> +
> + /* EBX contains a pointer to the bootinfo struct */
> + *p++ = 0xbb; /* MOV EBX,imm32 */
> + *p++ = bootinfo;
> + *p++ = bootinfo >> 8;
> + *p++ = bootinfo >> 16;
> + *p++ = bootinfo >> 24;
> +
> + /* EAX has to contain the following magic */
> + *p++ = 0xb8; /* MOV EAX,0x2badb002 */
> + *p++ = 0x02;
> + *p++ = 0xb0;
> + *p++ = 0xad;
> + *p++ = 0x2b;
> +
> + /* Jump off to the kernel */
> + *p++ = 0xea; /* JMP */
> + *p++ = mh_entry_addr; /* IP */
> + *p++ = mh_entry_addr >> 8;
> + *p++ = mh_entry_addr >> 16;
> + *p++ = mh_entry_addr >> 24;
> + *p++ = 0x08;
> + *p++ = 0x00;
> +
> + { /* GDT loading */
> + uint32_t gdt_base = 0x00007c00 + (p - bootsect); // 0x00007c00 is
> the first IP;
> + uint32_t gdtr = gdt_base + 0x28;
> + uint8_t gdt[] = { // GDT base: 0x00000100
> + // 0x00
> + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> + // 0x08: code segment (base=0, limit=0xfffff, type=32bit code
> exec/read, DPL=0, 4k)
> + 0xff, 0xff, 0x00, 0x00, 0x00, 0x9a, 0xcf, 0x00,
> + // 0x10: data segment (base=0, limit=0xfffff, type=32bit data
> read/write, DPL=0, 4k)
> + 0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0xcf, 0x00,
> + // 0x18: code segment (base=0, limit=0x0ffff, type=16bit code
> exec/read/conf, DPL=0, 1b)
> + 0xff, 0xff, 0x00, 0x00, 0x00, 0x9e, 0x00, 0x00,
> + // 0x20: data segment (base=0, limit=0x0ffff, type=16bit data
> read/write, DPL=0, 1b)
> + 0xff, 0xff, 0x00, 0x00, 0x00, 0x92, 0x00, 0x00,
> + // 0x28: gdtdesc
> + 0x27, 0x00, gdt_base, gdt_base >> 8, gdt_base >> 16, gdt_base >>
> 24
> + };
> +
> + memcpy(p, gdt, sizeof(gdt));
> + p+=sizeof(gdt);
> + *pgdt++ = gdtr;
> + *pgdt++ = gdtr >> 8;
> + *pgdt++ = gdtr >> 16;
> + *pgdt++ = gdtr >> 24;
> + }
> +
Is it really necessary to have *that much* assembly code within hw/pc.c?
I would rather see multiboot support as a small image generated from
C and/or assembly code, loaded either with -hda or with a new option
having the same effect. This code could read the NVRAM to get the
variables it needs.
--
.''`. Aurelien Jarno | GPG: 1024D/F1BCDB73
: :' : Debian developer | Electrical Engineer
`. `' [EMAIL PROTECTED] | [EMAIL PROTECTED]
`- people.debian.org/~aurel32 | www.aurel32.net
