diff options
Diffstat (limited to 'payloads/libpayload/arch/arm64/exception_asm.S')
| -rw-r--r-- | payloads/libpayload/arch/arm64/exception_asm.S | 152 |
1 files changed, 97 insertions, 55 deletions
diff --git a/payloads/libpayload/arch/arm64/exception_asm.S b/payloads/libpayload/arch/arm64/exception_asm.S index d428940730..efa3f9d7e2 100644 --- a/payloads/libpayload/arch/arm64/exception_asm.S +++ b/payloads/libpayload/arch/arm64/exception_asm.S @@ -27,19 +27,25 @@ * SUCH DAMAGE. */ +#include <arch/asm.h> +#include <arch/exception.h> + /* Macro for exception entry * Store x30 before any branch - * Branch to exception_prologue to save rest of the registers + * Branch to exception_prologue to save rest and switch stacks * Move exception id into x1 - * Branch to exception_handler + * Branch to exception_dispatch (exception C entry point) + * Branch to exception_return to return from exception */ .macro eentry lbl id .align 7 \lbl: - stp x30, xzr, [sp, #-16]! + /* Note: SP points to exception_state (see exception_set_state_ptr) */ + str x30, [sp, #EXCEPTION_STATE_REG(30)] bl exception_prologue mov x1, \id - bl exception_handler + bl exception_dispatch + b exception_return .endm /* Exception table has 16 entries and each of 128 bytes @@ -68,64 +74,100 @@ eentry irq_elx_32,#13 eentry fiq_elx_32,#14 eentry serror_elx_32,#15 -exception_prologue: - /* Save all registers x0-x29 */ - stp x28, x29, [sp, #-16]! - stp x26, x27, [sp, #-16]! - stp x24, x25, [sp, #-16]! - stp x22, x23, [sp, #-16]! - stp x20, x21, [sp, #-16]! - stp x18, x19, [sp, #-16]! - stp x16, x17, [sp, #-16]! - stp x14, x15, [sp, #-16]! - stp x12, x13, [sp, #-16]! - stp x10, x11, [sp, #-16]! - stp x8, x9, [sp, #-16]! - stp x6, x7, [sp, #-16]! - stp x4, x5, [sp, #-16]! - stp x2, x3, [sp, #-16]! - stp x0, x1, [sp, #-16]! - - /* Save the exception reason on stack */ - mrs x1, esr_el2 +/* This code must match the layout of struct exception_state (minus x30) */ +ENTRY(exception_prologue) + /* Save registers x0-x29 */ + stp x28, x29, [sp, #EXCEPTION_STATE_REG(28)] + stp x26, x27, [sp, #EXCEPTION_STATE_REG(26)] + stp x24, x25, [sp, #EXCEPTION_STATE_REG(24)] + stp x22, x23, [sp, #EXCEPTION_STATE_REG(22)] + stp x20, x21, [sp, #EXCEPTION_STATE_REG(20)] + stp x18, x19, [sp, #EXCEPTION_STATE_REG(18)] + stp x16, x17, [sp, #EXCEPTION_STATE_REG(16)] + stp x14, x15, [sp, #EXCEPTION_STATE_REG(14)] + stp x12, x13, [sp, #EXCEPTION_STATE_REG(12)] + stp x10, x11, [sp, #EXCEPTION_STATE_REG(10)] + stp x8, x9, [sp, #EXCEPTION_STATE_REG(8)] + stp x6, x7, [sp, #EXCEPTION_STATE_REG(6)] + stp x4, x5, [sp, #EXCEPTION_STATE_REG(4)] + stp x2, x3, [sp, #EXCEPTION_STATE_REG(2)] + stp x0, x1, [sp, #EXCEPTION_STATE_REG(0)] + + /* Save the stack pointer and SPSR */ + mrs x1, sp_el0 + mrs x0, spsr_el2 + stp x0, x1, [sp, #EXCEPTION_STATE_SPSR] - /* Save the return address on stack */ + /* Save return address (ELR) and exception syndrome */ + mrs x1, esr_el2 mrs x0, elr_el2 - stp x0, x1, [sp, #-16]! + stp x0, x1, [sp, #EXCEPTION_STATE_ELR] + + /* Now switch to the actual exception stack. Keep a pointer to the + exception_state structure in x0 as an argument for dispatch(). */ + mov x0, sp + adrp x1, exception_stack_end + ldr x1, [x1, :lo12:exception_stack_end] + msr SPSel, #0 + mov sp, x1 ret +ENDPROC(exception_prologue) -exception_handler: - /* Save address of saved registers into x0 - * This acts as first argument to exception_dispatch - */ - mov x0, sp - bl exception_dispatch +ENTRY(exception_return) + /* Switch SP back to the exception_state structure */ + msr SPSel, #1 - /* Pop return address saved on stack */ - ldp x0, x1, [sp], #16 + /* Restore return address (ELR) -- skip ESR (unneeded for return) */ + ldr x0, [sp, #EXCEPTION_STATE_ELR] msr elr_el2, x0 - msr esr_el2, x1 - /* Pop exception reason saved on stack, followed by regs x0-x30 */ - ldp x0, x1, [sp], #16 - ldp x2, x3, [sp], #16 - ldp x4, x5, [sp], #16 - ldp x6, x7, [sp], #16 - ldp x8, x9, [sp], #16 - ldp x10, x11, [sp], #16 - ldp x12, x13, [sp], #16 - ldp x14, x15, [sp], #16 - ldp x16, x17, [sp], #16 - ldp x18, x19, [sp], #16 - ldp x20, x21, [sp], #16 - ldp x22, x23, [sp], #16 - ldp x24, x25, [sp], #16 - ldp x26, x27, [sp], #16 - ldp x28, x29, [sp], #16 - ldp x30, xzr, [sp], #16 + + /* Restore stack pointer and SPSR */ + ldp x0, x1, [sp, #EXCEPTION_STATE_SPSR] + msr spsr_el2, x0 + msr sp_el0, x1 + + /* Restore all registers (x0-x30) */ + ldp x0, x1, [sp, #EXCEPTION_STATE_REG(0)] + ldp x2, x3, [sp, #EXCEPTION_STATE_REG(2)] + ldp x4, x5, [sp, #EXCEPTION_STATE_REG(4)] + ldp x6, x7, [sp, #EXCEPTION_STATE_REG(6)] + ldp x8, x9, [sp, #EXCEPTION_STATE_REG(8)] + ldp x10, x11, [sp, #EXCEPTION_STATE_REG(10)] + ldp x12, x13, [sp, #EXCEPTION_STATE_REG(12)] + ldp x14, x15, [sp, #EXCEPTION_STATE_REG(14)] + ldp x16, x17, [sp, #EXCEPTION_STATE_REG(16)] + ldp x18, x19, [sp, #EXCEPTION_STATE_REG(18)] + ldp x20, x21, [sp, #EXCEPTION_STATE_REG(20)] + ldp x22, x23, [sp, #EXCEPTION_STATE_REG(22)] + ldp x24, x25, [sp, #EXCEPTION_STATE_REG(24)] + ldp x26, x27, [sp, #EXCEPTION_STATE_REG(26)] + ldp x28, x29, [sp, #EXCEPTION_STATE_REG(28)] + ldr x30, [sp, #EXCEPTION_STATE_REG(30)] + + /* Return from exception */ eret +ENDPROC(exception_return) - .global set_vbar -set_vbar: - msr vbar_el2, x0 + /* + * We have two stack pointers on AArch64: SP_EL0 (which despite the + * naming is used in all ELs) and SP_EL2. We can select which one to + * use by writing to SPSel. Normally we're using SP_EL0, but on + * exception entry it automatically switches to SP_EL2. + * + * It is important for exception reentrancy to switch back to SP_EL0 + * while handling the exception. We only need SP_EL2 for the assembly + * exception entry and exit code that stores all register state + * (including the old SP_EL0, before we switch to the real exception + * stack). Rather than having yet another stack to push/pop those + * register values on so that we can later sort them into the + * exception_state structure, it's much easier to just make SP_EL2 point + * directly to exception_state and just use it as a normal base register + * rather than a real stack. This function sets that up. + */ +ENTRY(exception_set_state_ptr) + msr SPSel, #1 + mov sp, x0 + msr SPSel, #0 ret +ENDPROC(exception_set_state_ptr) |