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 Signed-off-by: Yinghai Lu <ying...@kernel.org> --- Documentation/x86/boot.txt | 38 ++++++++++++++++++++++++++++++++++++ arch/x86/boot/compressed/head_64.S | 22 ++++++++++++--------- 2 files changed, 51 insertions(+), 9 deletions(-) diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt index 18ca9fb..24cc542 100644 --- a/Documentation/x86/boot.txt +++ b/Documentation/x86/boot.txt @@ -1042,6 +1042,44 @@ 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 +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 +should be allocated under or above 4G and initialized to all zero. +Then the setup header from offset 0x01f1 of kernel image on should be +loaded into struct boot_params and examined. The end of setup header +can be calculated as follow: + + 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 that +described in zero-page.txt. + +After setting up the struct boot_params, the boot loader can load the +64-bit kernel in the same way as that of 16-bit boot protocol, but +kernel could be 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 5c80b94..aaafd4e 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, could not be changed! + * If we come here directly from a bootloader, + * kernel(text+data+bss+brk) ramdisk, zero_page, command line + * all need to be under 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, could not be changed! * 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 /* -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/