diff options
Diffstat (limited to 'Documentation/x86/boot.txt')
| -rw-r--r-- | Documentation/x86/boot.txt | 135 |
1 files changed, 124 insertions, 11 deletions
diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt index 9b7221a86df..a75e3adaa39 100644 --- a/Documentation/x86/boot.txt +++ b/Documentation/x86/boot.txt @@ -54,6 +54,13 @@ Protocol 2.10: (Kernel 2.6.31) Added a protocol for relaxed alignment beyond the kernel_alignment added, new init_size and pref_address fields. Added extended boot loader IDs. +Protocol 2.11: (Kernel 3.6) Added a field for offset of EFI handover + protocol entry point. + +Protocol 2.12: (Kernel 3.8) Added the xloadflags field and extension fields + to struct boot_params for loading bzImage and ramdisk + above 4G in 64bit. + **** MEMORY LAYOUT The traditional memory map for the kernel loader, used for Image or @@ -175,11 +182,11 @@ Offset Proto Name Meaning 0226/1 2.02+(3 ext_loader_ver Extended boot loader version 0227/1 2.02+(3 ext_loader_type Extended boot loader ID 0228/4 2.02+ cmd_line_ptr 32-bit pointer to the kernel command line -022C/4 2.03+ ramdisk_max Highest legal initrd address +022C/4 2.03+ initrd_addr_max Highest legal initrd address 0230/4 2.05+ kernel_alignment Physical addr alignment required for kernel 0234/1 2.05+ relocatable_kernel Whether kernel is relocatable or not 0235/1 2.10+ min_alignment Minimum alignment, as a power of two -0236/2 N/A pad3 Unused +0236/2 2.12+ xloadflags Boot protocol option flags 0238/4 2.06+ cmdline_size Maximum size of the kernel command line 023C/4 2.07+ hardware_subarch Hardware subarchitecture 0240/8 2.07+ hardware_subarch_data Subarchitecture-specific data @@ -189,6 +196,7 @@ Offset Proto Name Meaning of struct setup_data 0258/8 2.10+ pref_address Preferred loading address 0260/4 2.10+ init_size Linear memory required during initialization +0264/4 2.11+ handover_offset Offset of handover entry point (1) For backwards compatibility, if the setup_sects field contains 0, the real value is 4. @@ -363,12 +371,13 @@ Protocol: 2.00+ ext_loader_type <- 0x05 ext_loader_ver <- 0x23 - Assigned boot loader ids: + Assigned boot loader ids (hexadecimal): + 0 LILO (0x00 reserved for pre-2.00 bootloader) 1 Loadlin 2 bootsect-loader (0x20, all other values reserved) 3 Syslinux - 4 Etherboot/gPXE + 4 Etherboot/gPXE/iPXE 5 ELILO 7 GRUB 8 U-Boot @@ -376,8 +385,12 @@ Protocol: 2.00+ A Gujin B Qemu C Arcturus Networks uCbootloader + D kexec-tools E Extended (see ext_loader_type) F Special (0xFF = undefined) + 10 Reserved + 11 Minimal Linux Bootloader <http://sebastian-plotz.blogspot.de> + 12 OVMF UEFI virtualization stack Please contact <hpa@zytor.com> if you need a bootloader ID value assigned. @@ -521,7 +534,7 @@ Protocol: 2.02+ zero, the kernel will assume that your boot loader does not support the 2.02+ protocol. -Field name: ramdisk_max +Field name: initrd_addr_max Type: read Offset/size: 0x22c/4 Protocol: 2.03+ @@ -574,6 +587,30 @@ Protocol: 2.10+ misaligned kernel. Therefore, a loader should typically try each power-of-two alignment from kernel_alignment down to this alignment. +Field name: xloadflags +Type: read +Offset/size: 0x236/2 +Protocol: 2.12+ + + This field is a bitmask. + + Bit 0 (read): XLF_KERNEL_64 + - If 1, this kernel has the legacy 64-bit entry point at 0x200. + + Bit 1 (read): XLF_CAN_BE_LOADED_ABOVE_4G + - If 1, kernel/boot_params/cmdline/ramdisk can be above 4G. + + Bit 2 (read): XLF_EFI_HANDOVER_32 + - If 1, the kernel supports the 32-bit EFI handoff entry point + given at handover_offset. + + Bit 3 (read): XLF_EFI_HANDOVER_64 + - If 1, the kernel supports the 64-bit EFI handoff entry point + given at handover_offset + 0x200. + + Bit 4 (read): XLF_EFI_KEXEC + - If 1, the kernel supports kexec EFI boot with EFI runtime support. + Field name: cmdline_size Type: read Offset/size: 0x238/4 @@ -623,9 +660,10 @@ Protocol: 2.08+ uncompressed data should be determined using the standard magic numbers. The currently supported compression formats are gzip (magic numbers 1F 8B or 1F 9E), bzip2 (magic number 42 5A), LZMA - (magic number 5D 00), and XZ (magic number FD 37). The uncompressed - payload is currently always ELF (magic number 7F 45 4C 46). - + (magic number 5D 00), XZ (magic number FD 37), and LZ4 (magic number + 02 21). The uncompressed payload is currently always ELF (magic + number 7F 45 4C 46). + Field name: payload_length Type: read Offset/size: 0x24c/4 @@ -674,7 +712,7 @@ Protocol: 2.10+ Field name: init_size Type: read -Offset/size: 0x25c/4 +Offset/size: 0x260/4 This field indicates the amount of linear contiguous memory starting at the kernel runtime start address that the kernel needs before it @@ -690,6 +728,16 @@ Offset/size: 0x25c/4 else runtime_start = pref_address +Field name: handover_offset +Type: read +Offset/size: 0x264/4 + + This field is the offset from the beginning of the kernel image to + the EFI handover protocol entry point. Boot loaders using the EFI + handover protocol to boot the kernel should jump to this offset. + + See EFI HANDOVER PROTOCOL below for more details. + **** THE IMAGE CHECKSUM @@ -996,7 +1044,7 @@ boot_params as that of 16-bit boot protocol, the boot loader should also fill the additional fields of the struct boot_params as that described in zero-page.txt. -After setupping the struct boot_params, the boot loader can load the +After setting up the struct boot_params, the boot loader can load the 32/64-bit kernel in the same way as that of 16-bit boot protocol. In 32-bit boot protocol, the kernel is started by jumping to the @@ -1006,7 +1054,72 @@ In 32-bit boot protocol, the kernel is started by jumping to the At entry, the CPU must be in 32-bit protected mode with paging disabled; a GDT must be loaded with the descriptors for selectors __BOOT_CS(0x10) and __BOOT_DS(0x18); both descriptors must be 4G flat -segment; __BOOS_CS must have execute/read permission, and __BOOT_DS +segment; __BOOT_CS must have execute/read permission, and __BOOT_DS must have read/write permission; CS must be __BOOT_CS and DS, ES, SS must be __BOOT_DS; interrupt must be disabled; %esi must hold the base address of the struct boot_params; %ebp, %edi and %ebx must be zero. + +**** 64-bit BOOT PROTOCOL + +For machine with 64bit cpus and 64bit kernel, we could use 64bit bootloader +and we need a 64-bit boot protocol. + +In 64-bit boot protocol, the first step in loading a Linux kernel +should be to setup the boot parameters (struct boot_params, +traditionally known as "zero page"). The memory for struct boot_params +could be allocated anywhere (even above 4G) and initialized to all zero. +Then, the setup header at offset 0x01f1 of kernel image on should be +loaded into struct boot_params and examined. The end of setup header +can be calculated as follows: + + 0x0202 + byte value at offset 0x0201 + +In addition to read/modify/write the setup header of the struct +boot_params as that of 16-bit boot protocol, the boot loader should +also fill the additional fields of the struct boot_params as described +in zero-page.txt. + +After setting up the struct boot_params, the boot loader can load +64-bit kernel in the same way as that of 16-bit boot protocol, but +kernel could be loaded above 4G. + +In 64-bit boot protocol, the kernel is started by jumping to the +64-bit kernel entry point, which is the start address of loaded +64-bit kernel plus 0x200. + +At entry, the CPU must be in 64-bit mode with paging enabled. +The range with setup_header.init_size from start address of loaded +kernel and zero page and command line buffer get ident mapping; +a GDT must be loaded with the descriptors for selectors +__BOOT_CS(0x10) and __BOOT_DS(0x18); both descriptors must be 4G flat +segment; __BOOT_CS must have execute/read permission, and __BOOT_DS +must have read/write permission; CS must be __BOOT_CS and DS, ES, SS +must be __BOOT_DS; interrupt must be disabled; %rsi must hold the base +address of the struct boot_params. + +**** EFI HANDOVER PROTOCOL + +This protocol allows boot loaders to defer initialisation to the EFI +boot stub. The boot loader is required to load the kernel/initrd(s) +from the boot media and jump to the EFI handover protocol entry point +which is hdr->handover_offset bytes from the beginning of +startup_{32,64}. + +The function prototype for the handover entry point looks like this, + + efi_main(void *handle, efi_system_table_t *table, struct boot_params *bp) + +'handle' is the EFI image handle passed to the boot loader by the EFI +firmware, 'table' is the EFI system table - these are the first two +arguments of the "handoff state" as described in section 2.3 of the +UEFI specification. 'bp' is the boot loader-allocated boot params. + +The boot loader *must* fill out the following fields in bp, + + o hdr.code32_start + o hdr.cmd_line_ptr + o hdr.cmdline_size + o hdr.ramdisk_image (if applicable) + o hdr.ramdisk_size (if applicable) + +All other fields should be zero. |