From: Vivek Goyal o x86_64 kernel needs to be compiled for 2MB aligned addresses. Currently we are using BUILD_BUG_ON() to warn the user if he has not done so. But looks like folks are not finding message very intutive and don't open the respective c file to find problem source. (Bug 8439) arch/x86_64/kernel/head64.c: In function 'x86_64_start_kernel': arch/x86_64/kernel/head64.c:70: error: size of array 'type name' is negative o Using preprocessor directive #error to print a better message if CONFIG_PHYSICAL_START is not aligned to 2MB boundary. Signed-off-by: Vivek Goyal Cc: Andi Kleen Cc: "Eric W. Biederman" Signed-off-by: Andrew Morton --- arch/x86_64/kernel/head64.c | 7 ------- include/asm-x86_64/page.h | 9 +++++++++ 2 files changed, 9 insertions(+), 7 deletions(-) diff -puN arch/x86_64/kernel/head64.c~x86_64-display-more-intutive-error-message-if-kernel-is-not-2mb-aligned arch/x86_64/kernel/head64.c --- a/arch/x86_64/kernel/head64.c~x86_64-display-more-intutive-error-message-if-kernel-is-not-2mb-aligned +++ a/arch/x86_64/kernel/head64.c @@ -62,13 +62,6 @@ void __init x86_64_start_kernel(char * r { int i; - /* - * Make sure kernel is aligned to 2MB address. Catching it at compile - * time is better. Change your config file and compile the kernel - * for a 2MB aligned address (CONFIG_PHYSICAL_START) - */ - BUILD_BUG_ON(CONFIG_PHYSICAL_START & (__KERNEL_ALIGN - 1)); - /* clear bss before set_intr_gate with early_idt_handler */ clear_bss(); diff -puN include/asm-x86_64/page.h~x86_64-display-more-intutive-error-message-if-kernel-is-not-2mb-aligned include/asm-x86_64/page.h --- a/include/asm-x86_64/page.h~x86_64-display-more-intutive-error-message-if-kernel-is-not-2mb-aligned +++ a/include/asm-x86_64/page.h @@ -80,6 +80,15 @@ extern unsigned long phys_base; #define __PHYSICAL_START CONFIG_PHYSICAL_START #define __KERNEL_ALIGN 0x200000 +/* + * Make sure kernel is aligned to 2MB address. Catching it at compile + * time is better. Change your config file and compile the kernel + * for a 2MB aligned address (CONFIG_PHYSICAL_START) + */ +#if (CONFIG_PHYSICAL_START % __KERNEL_ALIGN) != 0 +#error "CONFIG_PHYSICAL_START must be a multiple of 2MB" +#endif + #define __START_KERNEL (__START_KERNEL_map + __PHYSICAL_START) #define __START_KERNEL_map _AC(0xffffffff80000000, UL) #define __PAGE_OFFSET _AC(0xffff810000000000, UL) _