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linux-brain/arch/arm/mm/proc-v7m.S
afzal mohammed 2ecb287998 ARM: 8926/1: v7m: remove register save to stack before svc 
r0-r3 & r12 registers are saved & restored, before & after svc
respectively. Intention was to preserve those registers across thread to
handler mode switch.

On v7-M, hardware saves the register context upon exception in AAPCS
complaint way. Restoring r0-r3 & r12 is done from stack location where
hardware saves it, not from the location on stack where these registers
were saved.

To clarify, on stm32f429 discovery board:

1. before svc, sp - 0x90009ff8
2. r0-r3,r12 saved to 0x90009ff8 - 0x9000a00b
3. upon svc, h/w decrements sp by 32 & pushes registers onto stack
4. after svc,  sp - 0x90009fd8
5. r0-r3,r12 restored from 0x90009fd8 - 0x90009feb

Above means r0-r3,r12 is not restored from the location where they are
saved, but since hardware pushes the registers onto stack, the registers
are restored correctly.

Note that during register saving to stack (step 2), it goes past
0x9000a000. And it seems, based on objdump, there are global symbols
residing there, and it perhaps can cause issues on a non-XIP Kernel
(on XIP, data section is setup later).

Based on the analysis above, manually saving registers onto stack is at
best no-op and at worst can cause data section corruption. Hence remove
storing of registers onto stack before svc.

Fixes: b70cd406d7 ("ARM: 8671/1: V7M: Preserve registers across switch from Thread to Handler mode")
Signed-off-by: afzal mohammed <afzal.mohd.ma@gmail.com>
Acked-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
2019-10-21 18:40:13 +01:00

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/* SPDX-License-Identifier: GPL-2.0-only */
/*
* linux/arch/arm/mm/proc-v7m.S
*
* Copyright (C) 2008 ARM Ltd.
* Copyright (C) 2001 Deep Blue Solutions Ltd.
*
* This is the "shell" of the ARMv7-M processor support.
*/
#include <linux/linkage.h>
#include <asm/assembler.h>
#include <asm/memory.h>
#include <asm/v7m.h>
#include "proc-macros.S"
ENTRY(cpu_v7m_proc_init)
ret lr
ENDPROC(cpu_v7m_proc_init)
ENTRY(cpu_v7m_proc_fin)
ret lr
ENDPROC(cpu_v7m_proc_fin)
/*
* cpu_v7m_reset(loc)
*
* Perform a soft reset of the system. Put the CPU into the
* same state as it would be if it had been reset, and branch
* to what would be the reset vector.
*
* - loc - location to jump to for soft reset
*/
.align 5
ENTRY(cpu_v7m_reset)
ret r0
ENDPROC(cpu_v7m_reset)
/*
* cpu_v7m_do_idle()
*
* Idle the processor (eg, wait for interrupt).
*
* IRQs are already disabled.
*/
ENTRY(cpu_v7m_do_idle)
wfi
ret lr
ENDPROC(cpu_v7m_do_idle)
ENTRY(cpu_v7m_dcache_clean_area)
ret lr
ENDPROC(cpu_v7m_dcache_clean_area)
/*
* There is no MMU, so here is nothing to do.
*/
ENTRY(cpu_v7m_switch_mm)
ret lr
ENDPROC(cpu_v7m_switch_mm)
.globl cpu_v7m_suspend_size
.equ cpu_v7m_suspend_size, 0
#ifdef CONFIG_ARM_CPU_SUSPEND
ENTRY(cpu_v7m_do_suspend)
ret lr
ENDPROC(cpu_v7m_do_suspend)
ENTRY(cpu_v7m_do_resume)
ret lr
ENDPROC(cpu_v7m_do_resume)
#endif
ENTRY(cpu_cm7_dcache_clean_area)
dcache_line_size r2, r3
movw r3, #:lower16:BASEADDR_V7M_SCB + V7M_SCB_DCCMVAC
movt r3, #:upper16:BASEADDR_V7M_SCB + V7M_SCB_DCCMVAC
1: str r0, [r3] @ clean D entry
add r0, r0, r2
subs r1, r1, r2
bhi 1b
dsb
ret lr
ENDPROC(cpu_cm7_dcache_clean_area)
ENTRY(cpu_cm7_proc_fin)
movw r2, #:lower16:(BASEADDR_V7M_SCB + V7M_SCB_CCR)
movt r2, #:upper16:(BASEADDR_V7M_SCB + V7M_SCB_CCR)
ldr r0, [r2]
bic r0, r0, #(V7M_SCB_CCR_DC | V7M_SCB_CCR_IC)
str r0, [r2]
ret lr
ENDPROC(cpu_cm7_proc_fin)
.section ".init.text", #alloc, #execinstr
__v7m_cm7_setup:
mov r8, #(V7M_SCB_CCR_DC | V7M_SCB_CCR_IC| V7M_SCB_CCR_BP)
b __v7m_setup_cont
/*
* __v7m_setup
*
* This should be able to cover all ARMv7-M cores.
*/
__v7m_setup:
mov r8, 0
__v7m_setup_cont:
@ Configure the vector table base address
ldr r0, =BASEADDR_V7M_SCB
ldr r12, =vector_table
str r12, [r0, V7M_SCB_VTOR]
@ enable UsageFault, BusFault and MemManage fault.
ldr r5, [r0, #V7M_SCB_SHCSR]
orr r5, #(V7M_SCB_SHCSR_USGFAULTENA | V7M_SCB_SHCSR_BUSFAULTENA | V7M_SCB_SHCSR_MEMFAULTENA)
str r5, [r0, #V7M_SCB_SHCSR]
@ Lower the priority of the SVC and PendSV exceptions
mov r5, #0x80000000
str r5, [r0, V7M_SCB_SHPR2] @ set SVC priority
mov r5, #0x00800000
str r5, [r0, V7M_SCB_SHPR3] @ set PendSV priority
@ SVC to switch to handler mode. Notice that this requires sp to
@ point to writeable memory because the processor saves
@ some registers to the stack.
badr r1, 1f
ldr r5, [r12, #11 * 4] @ read the SVC vector entry
str r1, [r12, #11 * 4] @ write the temporary SVC vector entry
dsb
mov r6, lr @ save LR
ldr sp, =init_thread_union + THREAD_START_SP
cpsie i
svc #0
1: cpsid i
/* Calculate exc_ret */
orr r10, lr, #EXC_RET_THREADMODE_PROCESSSTACK
ldmia sp, {r0-r3, r12}
str r5, [r12, #11 * 4] @ restore the original SVC vector entry
mov lr, r6 @ restore LR
@ Special-purpose control register
mov r1, #1
msr control, r1 @ Thread mode has unpriviledged access
@ Configure caches (if implemented)
teq r8, #0
stmiane sp, {r0-r6, lr} @ v7m_invalidate_l1 touches r0-r6
blne v7m_invalidate_l1
teq r8, #0 @ re-evalutae condition
ldmiane sp, {r0-r6, lr}
@ Configure the System Control Register to ensure 8-byte stack alignment
@ Note the STKALIGN bit is either RW or RAO.
ldr r0, [r0, V7M_SCB_CCR] @ system control register
orr r0, #V7M_SCB_CCR_STKALIGN
orr r0, r0, r8
ret lr
ENDPROC(__v7m_setup)
/*
* Cortex-M7 processor functions
*/
globl_equ cpu_cm7_proc_init, cpu_v7m_proc_init
globl_equ cpu_cm7_reset, cpu_v7m_reset
globl_equ cpu_cm7_do_idle, cpu_v7m_do_idle
globl_equ cpu_cm7_switch_mm, cpu_v7m_switch_mm
define_processor_functions v7m, dabort=nommu_early_abort, pabort=legacy_pabort, nommu=1
define_processor_functions cm7, dabort=nommu_early_abort, pabort=legacy_pabort, nommu=1
.section ".rodata"
string cpu_arch_name, "armv7m"
string cpu_elf_name "v7m"
string cpu_v7m_name "ARMv7-M"
.section ".proc.info.init", #alloc
.macro __v7m_proc name, initfunc, cache_fns = nop_cache_fns, hwcaps = 0, proc_fns = v7m_processor_functions
.long 0 /* proc_info_list.__cpu_mm_mmu_flags */
.long 0 /* proc_info_list.__cpu_io_mmu_flags */
initfn \initfunc, \name
.long cpu_arch_name
.long cpu_elf_name
.long HWCAP_HALF | HWCAP_THUMB | HWCAP_FAST_MULT | \hwcaps
.long cpu_v7m_name
.long \proc_fns
.long 0 /* proc_info_list.tlb */
.long 0 /* proc_info_list.user */
.long \cache_fns
.endm
/*
* Match ARM Cortex-M7 processor.
*/
.type __v7m_cm7_proc_info, #object
__v7m_cm7_proc_info:
.long 0x410fc270 /* ARM Cortex-M7 0xC27 */
.long 0xff0ffff0 /* Mask off revision, patch release */
__v7m_proc __v7m_cm7_proc_info, __v7m_cm7_setup, hwcaps = HWCAP_EDSP, cache_fns = v7m_cache_fns, proc_fns = cm7_processor_functions
.size __v7m_cm7_proc_info, . - __v7m_cm7_proc_info
/*
* Match ARM Cortex-M4 processor.
*/
.type __v7m_cm4_proc_info, #object
__v7m_cm4_proc_info:
.long 0x410fc240 /* ARM Cortex-M4 0xC24 */
.long 0xff0ffff0 /* Mask off revision, patch release */
__v7m_proc __v7m_cm4_proc_info, __v7m_setup, hwcaps = HWCAP_EDSP
.size __v7m_cm4_proc_info, . - __v7m_cm4_proc_info
/*
* Match ARM Cortex-M3 processor.
*/
.type __v7m_cm3_proc_info, #object
__v7m_cm3_proc_info:
.long 0x410fc230 /* ARM Cortex-M3 0xC23 */
.long 0xff0ffff0 /* Mask off revision, patch release */
__v7m_proc __v7m_cm3_proc_info, __v7m_setup
.size __v7m_cm3_proc_info, . - __v7m_cm3_proc_info
/*
* Match any ARMv7-M processor core.
*/
.type __v7m_proc_info, #object
__v7m_proc_info:
.long 0x000f0000 @ Required ID value
.long 0x000f0000 @ Mask for ID
__v7m_proc __v7m_proc_info, __v7m_setup
.size __v7m_proc_info, . - __v7m_proc_info
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