From 09c205afde70c15f20ca76ba0a57409dad175fd0 Mon Sep 17 00:00:00 2001 From: "H. Peter Anvin" Date: Sun, 27 Jan 2013 10:43:28 -0800 Subject: x86, boot: Define the 2.12 bzImage boot protocol Define the 2.12 bzImage boot protocol: add xloadflags and additional fields to allow the command line, initramfs and struct boot_params to live above the 4 GiB mark. The xloadflags now communicates if this is a 64-bit kernel with the legacy 64-bit entry point and which of the EFI handover entry points are supported. Avoid adding new read flags to loadflags because of claimed bootloaders testing the whole byte for == 1 to determine bzImageness at least until the issue can be researched further. This is based on patches by Yinghai Lu and David Woodhouse. Originally-by: Yinghai Lu Originally-by: David Woodhouse Acked-by: Yinghai Lu Acked-by: David Woodhouse Acked-by: Matt Fleming Signed-off-by: H. Peter Anvin Link: http://lkml.kernel.org/r/1359058816-7615-26-git-send-email-yinghai@kernel.org Cc: Rob Landley Cc: Gokul Caushik Cc: Josh Triplett Cc: Joe Millenbach --- Documentation/x86/boot.txt | 27 ++++++++++++++++++++++++++- Documentation/x86/zero-page.txt | 4 ++++ 2 files changed, 30 insertions(+), 1 deletion(-) (limited to 'Documentation/x86') diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt index 406d82d5d2bb..3edb4c2887a1 100644 --- a/Documentation/x86/boot.txt +++ b/Documentation/x86/boot.txt @@ -57,6 +57,10 @@ Protocol 2.10: (Kernel 2.6.31) Added a protocol for relaxed alignment Protocol 2.11: (Kernel 3.6) Added a field for offset of EFI handover protocol entry point. +Protocol 2.12: (Kernel 3.9) Added the xloadflags field and extension fields + to struct boot_params for for loading bzImage and ramdisk + above 4G in 64bit. + **** MEMORY LAYOUT The traditional memory map for the kernel loader, used for Image or @@ -182,7 +186,7 @@ Offset Proto Name Meaning 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 @@ -582,6 +586,27 @@ 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. + Field name: cmdline_size Type: read Offset/size: 0x238/4 diff --git a/Documentation/x86/zero-page.txt b/Documentation/x86/zero-page.txt index cf5437deda81..199f453cb4de 100644 --- a/Documentation/x86/zero-page.txt +++ b/Documentation/x86/zero-page.txt @@ -19,6 +19,9 @@ Offset Proto Name Meaning 090/010 ALL hd1_info hd1 disk parameter, OBSOLETE!! 0A0/010 ALL sys_desc_table System description table (struct sys_desc_table) 0B0/010 ALL olpc_ofw_header OLPC's OpenFirmware CIF and friends +0C0/004 ALL ext_ramdisk_image ramdisk_image high 32bits +0C4/004 ALL ext_ramdisk_size ramdisk_size high 32bits +0C8/004 ALL ext_cmd_line_ptr cmd_line_ptr high 32bits 140/080 ALL edid_info Video mode setup (struct edid_info) 1C0/020 ALL efi_info EFI 32 information (struct efi_info) 1E0/004 ALL alk_mem_k Alternative mem check, in KB @@ -27,6 +30,7 @@ Offset Proto Name Meaning 1E9/001 ALL eddbuf_entries Number of entries in eddbuf (below) 1EA/001 ALL edd_mbr_sig_buf_entries Number of entries in edd_mbr_sig_buffer (below) +1EF/001 ALL sentinel Used to detect broken bootloaders 290/040 ALL edd_mbr_sig_buffer EDD MBR signatures 2D0/A00 ALL e820_map E820 memory map table (array of struct e820entry) -- cgit v1.2.3 From 8ee2f2dfdbdfe1851fcc0191b2d4faa4c26a39fb Mon Sep 17 00:00:00 2001 From: Yinghai Lu Date: Thu, 24 Jan 2013 12:20:07 -0800 Subject: x86, boot: Update comments about entries for 64bit image Now 64bit entry is fixed on 0x200, can not be changed anymore. Update the comments to reflect that. Also put info about it in boot.txt -v2: fix some grammar error Signed-off-by: Yinghai Lu Link: http://lkml.kernel.org/r/1359058816-7615-27-git-send-email-yinghai@kernel.org Cc: Rob Landley Cc: Matt Fleming Signed-off-by: H. Peter Anvin --- Documentation/x86/boot.txt | 38 ++++++++++++++++++++++++++++++++++++++ arch/x86/boot/compressed/head_64.S | 22 +++++++++++++--------- 2 files changed, 51 insertions(+), 9 deletions(-) (limited to 'Documentation/x86') diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt index 3edb4c2887a1..0e383169839a 100644 --- a/Documentation/x86/boot.txt +++ b/Documentation/x86/boot.txt @@ -1054,6 +1054,44 @@ 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 diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S index 5c80b94f6c4a..d9ae9a4ffcb9 100644 --- a/arch/x86/boot/compressed/head_64.S +++ b/arch/x86/boot/compressed/head_64.S @@ -37,6 +37,12 @@ __HEAD .code32 ENTRY(startup_32) + /* + * 32bit entry is 0 and it is ABI so immutable! + * If we come here directly from a bootloader, + * kernel(text+data+bss+brk) ramdisk, zero_page, command line + * all need to be under the 4G limit. + */ cld /* * Test KEEP_SEGMENTS flag to see if the bootloader is asking @@ -182,20 +188,18 @@ ENTRY(startup_32) lret ENDPROC(startup_32) - /* - * Be careful here startup_64 needs to be at a predictable - * address so I can export it in an ELF header. Bootloaders - * should look at the ELF header to find this address, as - * it may change in the future. - */ .code64 .org 0x200 ENTRY(startup_64) /* + * 64bit entry is 0x200 and it is ABI so immutable! * We come here either from startup_32 or directly from a - * 64bit bootloader. If we come here from a bootloader we depend on - * an identity mapped page table being provied that maps our - * entire text+data+bss and hopefully all of memory. + * 64bit bootloader. + * If we come here from a bootloader, kernel(text+data+bss+brk), + * ramdisk, zero_page, command line could be above 4G. + * We depend on an identity mapped page table being provided + * that maps our entire kernel(text+data+bss+brk), zero page + * and command line. */ #ifdef CONFIG_EFI_STUB /* -- cgit v1.2.3