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linux-pinenote/arch/arm/kernel/entry-header.S
Daniel Thompson a18f36453e ARM: 8266/1: Remove early stack deallocation from restore_user_regs 
Currently restore_user_regs deallocates the SVC stack early in
its execution and relies on no exception being taken between
the deallocation and the registers being restored. The introduction
of a default FIQ handler that also uses the SVC stack breaks this
assumption and can result in corrupted register state.

This patch works around the problem by removing the early
stack deallocation and using r2 as a temporary instead. I have
not found a way to do this without introducing an extra mov
instruction to the macro.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2015-01-12 19:26:57 +00:00

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#include <linux/init.h>
#include <linux/linkage.h>
#include <asm/assembler.h>
#include <asm/asm-offsets.h>
#include <asm/errno.h>
#include <asm/thread_info.h>
#include <asm/v7m.h>
@ Bad Abort numbers
@ -----------------
@
#define BAD_PREFETCH 0
#define BAD_DATA 1
#define BAD_ADDREXCPTN 2
#define BAD_IRQ 3
#define BAD_UNDEFINSTR 4
@
@ Most of the stack format comes from struct pt_regs, but with
@ the addition of 8 bytes for storing syscall args 5 and 6.
@ This _must_ remain a multiple of 8 for EABI.
@
#define S_OFF 8
/*
* The SWI code relies on the fact that R0 is at the bottom of the stack
* (due to slow/fast restore user regs).
*/
#if S_R0 != 0
#error "Please fix"
#endif
.macro zero_fp
#ifdef CONFIG_FRAME_POINTER
mov fp, #0
#endif
.endm
#ifdef CONFIG_ALIGNMENT_TRAP
#define ATRAP(x...) x
#else
#define ATRAP(x...)
#endif
.macro alignment_trap, rtmp1, rtmp2, label
#ifdef CONFIG_ALIGNMENT_TRAP
mrc p15, 0, \rtmp2, c1, c0, 0
ldr \rtmp1, \label
ldr \rtmp1, [\rtmp1]
teq \rtmp1, \rtmp2
mcrne p15, 0, \rtmp1, c1, c0, 0
#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
@ ensure bit 0 is cleared in the PC, otherwise behaviour is
@ unpredictable
bic r4, #1
@ 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
@ available. Should only be called from SVC mode
@
.macro store_user_sp_lr, rd, rtemp, offset = 0
mrs \rtemp, cpsr
eor \rtemp, \rtemp, #(SVC_MODE ^ SYSTEM_MODE)
msr cpsr_c, \rtemp @ switch to the SYS mode
str sp, [\rd, #\offset] @ save sp_usr
str lr, [\rd, #\offset + 4] @ save lr_usr
eor \rtemp, \rtemp, #(SVC_MODE ^ SYSTEM_MODE)
msr cpsr_c, \rtemp @ switch back to the SVC mode
.endm
.macro load_user_sp_lr, rd, rtemp, offset = 0
mrs \rtemp, cpsr
eor \rtemp, \rtemp, #(SVC_MODE ^ SYSTEM_MODE)
msr cpsr_c, \rtemp @ switch to the SYS mode
ldr sp, [\rd, #\offset] @ load sp_usr
ldr lr, [\rd, #\offset + 4] @ load lr_usr
eor \rtemp, \rtemp, #(SVC_MODE ^ SYSTEM_MODE)
msr cpsr_c, \rtemp @ switch back to the SVC mode
.endm
#ifndef CONFIG_THUMB2_KERNEL
.macro svc_exit, rpsr, irq = 0
.if \irq != 0
@ IRQs already off
#ifdef CONFIG_TRACE_IRQFLAGS
@ The parent context IRQs must have been enabled to get here in
@ the first place, so there's no point checking the PSR I bit.
bl trace_hardirqs_on
#endif
.else
@ IRQs off again before pulling preserved data off the stack
disable_irq_notrace
#ifdef CONFIG_TRACE_IRQFLAGS
tst \rpsr, #PSR_I_BIT
bleq trace_hardirqs_on
tst \rpsr, #PSR_I_BIT
blne trace_hardirqs_off
#endif
.endif
msr spsr_cxsf, \rpsr
#if defined(CONFIG_CPU_V6) || defined(CONFIG_CPU_32v6K)
@ We must avoid clrex due to Cortex-A15 erratum #830321
sub r0, sp, #4 @ uninhabited address
strex r1, r2, [r0] @ clear the exclusive monitor
#endif
ldmia sp, {r0 - pc}^ @ load r0 - pc, cpsr
.endm
@
@ svc_exit_via_fiq - like svc_exit but switches to FIQ mode before exit
@
@ This macro acts in a similar manner to svc_exit but switches to FIQ
@ mode to restore the final part of the register state.
@
@ We cannot use the normal svc_exit procedure because that would
@ clobber spsr_svc (FIQ could be delivered during the first few
@ instructions of vector_swi meaning its contents have not been
@ saved anywhere).
@
@ Note that, unlike svc_exit, this macro also does not allow a caller
@ supplied rpsr. This is because the FIQ exceptions are not re-entrant
@ and the handlers cannot call into the scheduler (meaning the value
@ on the stack remains correct).
@
.macro svc_exit_via_fiq
mov r0, sp
ldmib r0, {r1 - r14} @ abort is deadly from here onward (it will
@ clobber state restored below)
msr cpsr_c, #FIQ_MODE | PSR_I_BIT | PSR_F_BIT
add r8, r0, #S_PC
ldr r9, [r0, #S_PSR]
msr spsr_cxsf, r9
ldr r0, [r0, #S_R0]
ldmia r8, {pc}^
.endm
.macro restore_user_regs, fast = 0, offset = 0
mov r2, sp
ldr r1, [r2, #\offset + S_PSR] @ get calling cpsr
ldr lr, [r2, #\offset + S_PC]! @ get pc
msr spsr_cxsf, r1 @ save in spsr_svc
#if defined(CONFIG_CPU_V6) || defined(CONFIG_CPU_32v6K)
@ We must avoid clrex due to Cortex-A15 erratum #830321
strex r1, r2, [r2] @ clear the exclusive monitor
#endif
.if \fast
ldmdb r2, {r1 - lr}^ @ get calling r1 - lr
.else
ldmdb r2, {r0 - lr}^ @ get calling r0 - lr
.endif
mov r0, r0 @ ARMv5T and earlier require a nop
@ after ldm {}^
add sp, sp, #\offset + S_FRAME_SIZE
movs pc, lr @ return & move spsr_svc into cpsr
.endm
#else /* CONFIG_THUMB2_KERNEL */
.macro svc_exit, rpsr, irq = 0
.if \irq != 0
@ IRQs already off
#ifdef CONFIG_TRACE_IRQFLAGS
@ The parent context IRQs must have been enabled to get here in
@ the first place, so there's no point checking the PSR I bit.
bl trace_hardirqs_on
#endif
.else
@ IRQs off again before pulling preserved data off the stack
disable_irq_notrace
#ifdef CONFIG_TRACE_IRQFLAGS
tst \rpsr, #PSR_I_BIT
bleq trace_hardirqs_on
tst \rpsr, #PSR_I_BIT
blne trace_hardirqs_off
#endif
.endif
ldr lr, [sp, #S_SP] @ top of the stack
ldrd r0, r1, [sp, #S_LR] @ calling lr and pc
@ We must avoid clrex due to Cortex-A15 erratum #830321
strex r2, r1, [sp, #S_LR] @ clear the exclusive monitor
stmdb lr!, {r0, r1, \rpsr} @ calling lr and rfe context
ldmia sp, {r0 - r12}
mov sp, lr
ldr lr, [sp], #4
rfeia sp!
.endm
@
@ svc_exit_via_fiq - like svc_exit but switches to FIQ mode before exit
@
@ For full details see non-Thumb implementation above.
@
.macro svc_exit_via_fiq
add r0, sp, #S_R2
ldr lr, [sp, #S_LR]
ldr sp, [sp, #S_SP] @ abort is deadly from here onward (it will
@ clobber state restored below)
ldmia r0, {r2 - r12}
mov r1, #FIQ_MODE | PSR_I_BIT | PSR_F_BIT
msr cpsr_c, r1
sub r0, #S_R2
add r8, r0, #S_PC
ldmia r0, {r0 - r1}
rfeia r8
.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
mov r2, sp
load_user_sp_lr r2, r3, \offset + S_SP @ calling sp, lr
ldr r1, [sp, #\offset + S_PSR] @ get calling cpsr
ldr lr, [sp, #\offset + S_PC] @ get pc
add sp, sp, #\offset + S_SP
msr spsr_cxsf, r1 @ save in spsr_svc
@ We must avoid clrex due to Cortex-A15 erratum #830321
strex r1, r2, [sp] @ clear the exclusive monitor
.if \fast
ldmdb sp, {r1 - r12} @ get calling r1 - r12
.else
ldmdb sp, {r0 - r12} @ get calling r0 - r12
.endif
add sp, sp, #S_FRAME_SIZE - S_SP
movs pc, lr @ return & move spsr_svc into cpsr
.endm
#endif /* ifdef CONFIG_CPU_V7M / else */
#endif /* !CONFIG_THUMB2_KERNEL */
/*
* Context tracking subsystem. Used to instrument transitions
* between user and kernel mode.
*/
.macro ct_user_exit, save = 1
#ifdef CONFIG_CONTEXT_TRACKING
.if \save
stmdb sp!, {r0-r3, ip, lr}
bl context_tracking_user_exit
ldmia sp!, {r0-r3, ip, lr}
.else
bl context_tracking_user_exit
.endif
#endif
.endm
.macro ct_user_enter, save = 1
#ifdef CONFIG_CONTEXT_TRACKING
.if \save
stmdb sp!, {r0-r3, ip, lr}
bl context_tracking_user_enter
ldmia sp!, {r0-r3, ip, lr}
.else
bl context_tracking_user_enter
.endif
#endif
.endm
/*
* These are the registers used in the syscall handler, and allow us to
* have in theory up to 7 arguments to a function - r0 to r6.
*
* r7 is reserved for the system call number for thumb mode.
*
* Note that tbl == why is intentional.
*
* We must set at least "tsk" and "why" when calling ret_with_reschedule.
*/
scno .req r7 @ syscall number
tbl .req r8 @ syscall table pointer
why .req r8 @ Linux syscall (!= 0)
tsk .req r9 @ current thread_info
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