/* * Kernel entry in assembly. This handles relocating the kernel so that it is * in both physical and virtual memory where we want it to be. We copy the * kernel to a different physical location if necessary, turn on the MMU, * setting up a dual-mapping if the kernel is not in physical memory at the * same place it was linked against. Finally, we jump into the kernel's main() * function in C using the address it is linked against. When the MMU gets * initialized fully later, it will remove the initial 1:1 mapping. */ .globl start start: str r1, machine_type /* Backup atags/machine type registers so we can access them later from C */ str r2, atags_ptr bl copy_kernel copy_kernel_lr: /* Used to calculate address at which kernel is currently loaded by copy_kernel */ bl setup_mmu ldr sp, =stack+0x10000 /* Set up the stack */ bl main 1: b 1b /* Halt */ copy_kernel: /* * Because we're not necessarily loaded at an address that's aligned the same * as where we're linked, copy the kernel over to fix that up. * * clobbers: * r0-r10 * returns: * r0 = new kernel base address */ sub r0, lr, $(copy_kernel_lr - start) /* r0 <- current address of start */ ldr r1, tt_section_align ands r2, r0, r1 /* If we're already aligned to 1mb, early out */ bxeq lr mov r2, r0 /* r2 <- r0 <- current address of start */ mov r3, #1 lsl r3, r3, #20 /* r3 <- 1mb */ add r0, r0, r3 bic r0, r0, r1 /* r0 <- new address of start */ sub r1, r0, r2 /* r1 <- offset between current and new start */ /* TODO only copy kernel image sections that aren't zeroed (leave out .bss) */ ldr r5, =start ldr r6, =kernel_end sub r6, r6, r5 add r6, r6, r2 /* r6 <- old kernel_end */ add r6, r6, #16 bic r6, r6, #0xf /* r6 <- old kernel_end (aligned to 16 bytes) */ add r5, r6, r1 /* r5 <- new kernel_end */ copy_kernel_loop: /* Copy the kernel to its new location, 16 bytes at a time. We do this * from the end to the begininning so we don't overwrite the old kernel if the * destination and source overlap. */ sub r6, r6, #16 sub r5, r5, #16 ldm r6, {r7, r8, r9, r10} stm r5, {r7, r8, r9, r10} subs r4, r5, r0 bne copy_kernel_loop add lr, lr, r1 /* Fixup link register for new kernel location */ bx lr setup_mmu: /* * Calculate the address at which we will store our translation table. * Currently, we store it just past the end of the kernel. Getting the physical * address of the end of the kernel is tricky, since kernel_end is the address * the end of the kernel is linked at, so we have to do a little math. * * arguments: * r0 = current kernel base address (physical), aligned to 1mb boundary * clobbers: * r0-r10 */ /* Find future virtual address of the translation table */ ldr r1, =kernel_end ldr r2, tt_base_align ands r3, r1, r2 mov r3, r1 addne r3, r1, r2 bic r2, r3, r2 /* r2 <- future virtual address of translation table */ str r2, tt_base_virtual /* Find physical address of the translation table */ ldr r1, =start sub r1, r2, r1 add r1, r0, r1 /* r1 <- physical address of translation table */ str r1, tt_base_physical /* How many sections do we need to map to make sure we have the kernel * and translation table covered? */ ldr r3, tt_base_align add r3, r3, r1 sub r3, r3, r0 lsr r3, r3, #20 add r3, r3, #1 /* r3 <- number of sections to map */ ldr r4, =start /* r4 <- kernel virtual start address */ lsr r5, r4, #18 /* 18 = 20 (1mb) - 2 (4 bytes per entry) */ add r5, r5, r1 /* r5 <- address of translation page entry for first kernel section (final mapping) */ mov r6, r0 /* r6 <- kernel physical start address */ lsr r7, r6, #18 /* 18 = 20 (1mb) - 2 (4 bytes per entry) */ add r7, r7, r1 /* r7 <- address of translation page entry for first kernel section (initial, 1:1 mapping) */ mov r8, #1 lsl r8, r8, #20 /* r8 <- 1mb */ mov r9, #0xc lsl r9, r9, #8 orr r9, r9, #2 /* r9 <- 0xc02, which means read/write at any priviledge level, and that it's a section w/o PXN bit set */ initial_tt_loop: /* Setup translation table entries for the translation table and kernel (domain 0) */ ldr r10, tt_section_align bic r10, r6, r10 orr r10, r10, r9 /* r9=0xc02, which means read/write at any priviledge level */ str r10, [r7] str r10, [r5] add r6, r6, r8 add r7, r7, #4 add r5, r5, #4 subs r3, r3, #1 bne initial_tt_loop mcr p15, 0, r1, c2, c0, 0 /* TTBR0 <- physical address of translation table */ /* Set access permissions for domain 0 to "Manager" */ mov r1, #0x3 mcr p15, 0, r1, c3, c0, 0 /* DACR */ /* Enable the MMU */ mrc p15, 0, r1, c1, c0, 0 /* SCTLR */ orr r1, r1, #0x1 mcr p15, 0, r1, c1, c0, 0 /* SCTLR */ /* Update lr for new memory mapping */ ldr r1, =start sub r0, r1, r0 add lr, lr, r0 bx lr /* Finally, we jump into the new memory mapping, which matches where we were linked */ tt_base_align: .word 0b111111111111111 /* 16k - 1 */ tt_section_align: .word 0b11111111111111111111 /* 1mb - 1 */ .globl tt_base_virtual tt_base_virtual: .word 0 .globl tt_base_physical tt_base_physical: .word 0 .globl atags_ptr atags_ptr: .word 0 .globl machine_type machine_type: .word 0 .comm stack, 0x10000 /* Reserve 64k for the stack in .bss */