diff options
Diffstat (limited to 'arch/arm/kernel/entry-header.S')
| -rw-r--r-- | arch/arm/kernel/entry-header.S | 124 |
1 files changed, 124 insertions, 0 deletions
diff --git a/arch/arm/kernel/entry-header.S b/arch/arm/kernel/entry-header.S index 160f3376ba6..de23a9beed1 100644 --- a/arch/arm/kernel/entry-header.S +++ b/arch/arm/kernel/entry-header.S @@ -5,6 +5,7 @@ #include <asm/asm-offsets.h> #include <asm/errno.h> #include <asm/thread_info.h> +#include <asm/v7m.h> @ Bad Abort numbers @ ----------------- @@ -44,6 +45,116 @@ #endif .endm +#ifdef CONFIG_CPU_V7M +/* + * ARMv7-M exception entry/exit macros. + * + * xPSR, ReturnAddress(), LR (R14), R12, R3, R2, R1, and R0 are + * automatically saved on the current stack (32 words) before + * switching to the exception stack (SP_main). + * + * If exception is taken while in user mode, SP_main is + * empty. Otherwise, SP_main is aligned to 64 bit automatically + * (CCR.STKALIGN set). + * + * Linux assumes that the interrupts are disabled when entering an + * exception handler and it may BUG if this is not the case. Interrupts + * are disabled during entry and reenabled in the exit macro. + * + * v7m_exception_slow_exit is used when returning from SVC or PendSV. + * When returning to kernel mode, we don't return from exception. + */ + .macro v7m_exception_entry + @ determine the location of the registers saved by the core during + @ exception entry. Depending on the mode the cpu was in when the + @ exception happend that is either on the main or the process stack. + @ Bit 2 of EXC_RETURN stored in the lr register specifies which stack + @ was used. + tst lr, #EXC_RET_STACK_MASK + mrsne r12, psp + moveq r12, sp + + @ we cannot rely on r0-r3 and r12 matching the value saved in the + @ exception frame because of tail-chaining. So these have to be + @ reloaded. + ldmia r12!, {r0-r3} + + @ Linux expects to have irqs off. Do it here before taking stack space + cpsid i + + sub sp, #S_FRAME_SIZE-S_IP + stmdb sp!, {r0-r11} + + @ load saved r12, lr, return address and xPSR. + @ r0-r7 are used for signals and never touched from now on. Clobbering + @ r8-r12 is OK. + mov r9, r12 + ldmia r9!, {r8, r10-r12} + + @ calculate the original stack pointer value. + @ r9 currently points to the memory location just above the auto saved + @ xPSR. + @ The cpu might automatically 8-byte align the stack. Bit 9 + @ of the saved xPSR specifies if stack aligning took place. In this case + @ another 32-bit value is included in the stack. + + tst r12, V7M_xPSR_FRAMEPTRALIGN + addne r9, r9, #4 + + @ store saved r12 using str to have a register to hold the base for stm + str r8, [sp, #S_IP] + add r8, sp, #S_SP + @ store r13-r15, xPSR + stmia r8!, {r9-r12} + @ store old_r0 + str r0, [r8] + .endm + + /* + * PENDSV and SVCALL are configured to have the same exception + * priorities. As a kernel thread runs at SVCALL execution priority it + * can never be preempted and so we will never have to return to a + * kernel thread here. + */ + .macro v7m_exception_slow_exit ret_r0 + cpsid i + ldr lr, =EXC_RET_THREADMODE_PROCESSSTACK + + @ read original r12, sp, lr, pc and xPSR + add r12, sp, #S_IP + ldmia r12, {r1-r5} + + @ an exception frame is always 8-byte aligned. To tell the hardware if + @ the sp to be restored is aligned or not set bit 9 of the saved xPSR + @ accordingly. + tst r2, #4 + subne r2, r2, #4 + orrne r5, V7M_xPSR_FRAMEPTRALIGN + biceq r5, V7M_xPSR_FRAMEPTRALIGN + + @ write basic exception frame + stmdb r2!, {r1, r3-r5} + ldmia sp, {r1, r3-r5} + .if \ret_r0 + stmdb r2!, {r0, r3-r5} + .else + stmdb r2!, {r1, r3-r5} + .endif + + @ restore process sp + msr psp, r2 + + @ restore original r4-r11 + ldmia sp!, {r0-r11} + + @ restore main sp + add sp, sp, #S_FRAME_SIZE-S_IP + + cpsie i + bx lr + .endm +#endif /* CONFIG_CPU_V7M */ + @ @ Store/load the USER SP and LR registers by switching to the SYS @ mode. Useful in Thumb-2 mode where "stm/ldm rd, {sp, lr}^" is not @@ -165,6 +276,18 @@ rfeia sp! .endm +#ifdef CONFIG_CPU_V7M + /* + * Note we don't need to do clrex here as clearing the local monitor is + * part of each exception entry and exit sequence. + */ + .macro restore_user_regs, fast = 0, offset = 0 + .if \offset + add sp, #\offset + .endif + v7m_exception_slow_exit ret_r0 = \fast + .endm +#else /* ifdef CONFIG_CPU_V7M */ .macro restore_user_regs, fast = 0, offset = 0 clrex @ clear the exclusive monitor mov r2, sp @@ -181,6 +304,7 @@ add sp, sp, #S_FRAME_SIZE - S_SP movs pc, lr @ return & move spsr_svc into cpsr .endm +#endif /* ifdef CONFIG_CPU_V7M / else */ .macro get_thread_info, rd mov \rd, sp |