[PATCH v2 5/5] Cortex-M3: Add support for exception handling
Uwe Kleine-König
u.kleine-koenig at pengutronix.de
Mon Mar 5 12:04:02 EST 2012
This patch implements the exception handling for the ARMv7-M
architecture (pretty different from the A or R profiles).
Initially this based on a patch by Catalin Marinas but was completely
reworked to use a pt_regs layout similar to the A profile.
Note this is broken in at least two ways:
- r0 isn't saved for signal restarting (should be easy)
- crashes early after reaching userspace.
Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
---
Hello,
To save r0, I'd readd OLD_R0 at the end of pt_regs (plus one buffer word
to get even alignment). Or would that already be unacceptable because
it's an ABI change, too?
Anyhow, this is (once more :-) a great opportunity for you to blame me
in public by pointing out why my machine crashes with this patch. But to
be honest this time I wouldn't mind because hopefully after describing
your findings I'd be able to fix the problem.
Best regards
Uwe
arch/arm/kernel/entry-common.S | 9 ++-
arch/arm/kernel/entry-header.S | 149 +++++++++++++++++++++++++++++++++++++++-
arch/arm/kernel/entry-v7m.S | 135 ++++++++++++++++++++++++++++++++++++
arch/arm/kernel/process.c | 8 ++
4 files changed, 299 insertions(+), 2 deletions(-)
create mode 100644 arch/arm/kernel/entry-v7m.S
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 9fd0ba9..953e517 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -345,6 +345,9 @@ ENDPROC(ftrace_stub)
.align 5
ENTRY(vector_swi)
+#ifdef CONFIG_CPU_V7M
+ v7m_exception_entry
+#else
sub sp, sp, #S_FRAME_SIZE
stmia sp, {r0 - r12} @ Calling r0 - r12
ARM( add r8, sp, #S_PC )
@@ -354,7 +357,11 @@ ENTRY(vector_swi)
mrs r8, spsr @ called from non-FIQ mode, so ok.
str lr, [sp, #S_PC] @ Save calling PC
str r8, [sp, #S_PSR] @ Save CPSR
+#endif
+#if XXX
+ /* XXX: fixme: we need to preserve r0 somewhere for signal stuff */
str r0, [sp, #S_OLD_R0] @ Save OLD_R0
+#endif
zero_fp
/*
@@ -473,7 +480,7 @@ __sys_trace:
adr lr, BSYM(__sys_trace_return) @ return address
mov scno, r0 @ syscall number (possibly new)
- add r1, sp, #S_R0 + S_OFF @ pointer to regs
+ add r1, sp, #S_OFF @ pointer to regs
cmp scno, #NR_syscalls @ check upper syscall limit
ldmccia r1, {r0 - r3} @ have to reload r0 - r3
ldrcc pc, [tbl, scno, lsl #2] @ call sys_* routine
diff --git a/arch/arm/kernel/entry-header.S b/arch/arm/kernel/entry-header.S
index 9a8531e..6e03c8b 100644
--- a/arch/arm/kernel/entry-header.S
+++ b/arch/arm/kernel/entry-header.S
@@ -26,7 +26,7 @@
* 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
+#if S_R0 != 0 && !defined(CONFIG_CPU_V7M)
#error "Please fix"
#endif
@@ -44,6 +44,144 @@
#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_fast_exit is used when returning from interrupts.
+ *
+ * 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
+ cpsid i
+ sub sp, #S_FRAME_SIZE
+ stmia sp, {r0-r12}
+
+ @ set r0 to 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, #0x4
+ mrsne r0, psp
+ addeq r0, sp, #S_FRAME_SIZE
+
+ add r0, r0, #20 @ skip over r0-r3, r12
+ ldmia r0!, {r1-r3} @ load saved lr, return address and xPSR
+
+ @ calculate the orignal stack pointer value.
+ @ r0 currently points to the memory location just above the auto saved
+ @ xPSR. If the FP extension is implemented and bit 4 of EXC_RETURN is 0
+ @ then space was allocated for FP state. That is space for 18 32-bit
+ @ values. (If FP extension is unimplemented, bit 4 is 1.)
+ @ Additionally 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 lr, #0x10
+ addeq r0, r0, #576
+
+ tst r3, #0x100
+ addne r0, r0, #4
+
+ @ save original sp, lr, return address, xPSR and EXC_RETURN
+ add r12, sp, #52
+ stmia r12, {r0-r3, lr}
+
+ @ restore registers for system calls
+ ldmia sp, {r0-r12}
+ .endm
+
+ .macro v7m_exception_fast_exit
+ @ read r12, sp, lr, return address, xPSR and EXC_RETURN
+ add r12, sp, #48
+ ldmia r12, {r1-r5, lr}
+
+ tst r5, #0x100
+ subne r2, r2, #4
+
+ tst lr, #0x10
+ subeq r2, r2, #576
+
+ stmdb r2!, {r1, r3-r5} @ write saved r12, lr, return address and xPSR
+
+ ldmia sp, {r1, r3-r5} @ read saved r0-r3
+ stmdb r2!, {r1, r3-r5} @ write r0-r3 to basic exception frame
+
+ tst lr, #0x4
+ msrne psp, r2
+
+ ldmia sp, {r0-r12}
+ add sp, #S_FRAME_SIZE
+ cpsie i
+ bx lr
+ .endm
+
+ .macro v7m_exception_slow_exit ret_r0
+ cpsid i
+ ldr lr, [sp, #S_EXCRET] @ read exception LR
+ tst lr, #0x8
+ bne 1f @ go to thread mode using exception return
+
+ /*
+ * return to kernel thread
+ * sp is already set up (and might be unset in pt_regs), so only
+ * restore r0-r12 and pc
+ */
+ ldmia sp, {r0-r12}
+ ldr lr, [sp, #S_PC]
+ add sp, sp, #S_FRAME_SIZE
+ cpsie i
+ bx lr
+
+ /*
+ * return to userspace
+ */
+1:
+ @ read original r12, sp, lr, pc, xPSR
+ add r12, sp, #48
+ ldmia r12, {r1-r5}
+
+ /* stack aligning */
+ tst r5, #0x100
+ subne r2, r2, #4
+
+ /* skip over stack space for fp extension */
+ tst lr, #0x10
+ subeq r2, r2, #576
+
+ /* write basic exception frame */
+ stmdb r2!, {r1, r3-r5} @ saved r12, lr, return address and xPSR
+ ldmia sp, {r1, r3-r5} @ read saved r0-r3
+ .if \ret_r0
+ stmdb r2!, {r0, r3-r5} @ restore r0-r3
+ .else
+ stmdb r2!, {r1, r3-r5} @ restore r0-r3
+ .endif
+
+ msr psp, r2
+
+ ldmia sp, {r0-r12} @ restore original r4-r11
+
+ add sp, #S_FRAME_SIZE @ restore the original MSP
+ 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
@@ -131,6 +269,14 @@
rfeia sp!
.endm
+#ifdef CONFIG_CPU_V7M
+ .macro restore_user_regs, fast = 0, offset = 0
+ .if \offset
+ add sp, #\offset
+ .endif
+ v7m_exception_slow_exit ret_r0 = \fast
+ .endm
+#else /* !CONFIG_CPU_V7M */
.macro restore_user_regs, fast = 0, offset = 0
clrex @ clear the exclusive monitor
mov r2, sp
@@ -147,6 +293,7 @@
add sp, sp, #S_FRAME_SIZE - S_SP
movs pc, lr @ return & move spsr_svc into cpsr
.endm
+#endif /* CONFIG_CPU_V7M */
.macro get_thread_info, rd
mov \rd, sp
diff --git a/arch/arm/kernel/entry-v7m.S b/arch/arm/kernel/entry-v7m.S
new file mode 100644
index 0000000..5bca10b
--- /dev/null
+++ b/arch/arm/kernel/entry-v7m.S
@@ -0,0 +1,135 @@
+/*
+ * linux/arch/arm/kernel/entry-v7m.S
+ *
+ * Copyright (C) 2008 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Low-level vector interface routines for the ARMv7-M architecture
+ */
+#include <asm/memory.h>
+#include <asm/glue.h>
+#include <asm/thread_notify.h>
+
+#include <mach/entry-macro.S>
+
+#include "entry-header.S"
+
+#ifdef CONFIG_PREEMPT
+#error "CONFIG_PREEMPT not supported on the current ARMv7M implementation"
+#endif
+#ifdef CONFIG_TRACE_IRQFLAGS
+#error "CONFIG_TRACE_IRQFLAGS not supported on the current ARMv7M implementation"
+#endif
+
+__invalid_entry:
+ v7m_exception_entry
+ adr r0, strerr
+ mrs r1, ipsr
+ mov r2, lr
+ mov r3, sp
+ bl printk
+ mov r0, sp
+ bl __show_regs
+1: b 1b
+ENDPROC(__invalid_entry)
+
+strerr: .asciz "\nUnhandled exception: IPSR = %08lx LR = %08lx SP = %08lx\n"
+
+ .align 2
+__irq_entry:
+ v7m_exception_entry
+
+ @
+ @ Invoke the IRQ handler
+ @
+ mrs r0, ipsr
+ and r0, #0xff
+ sub r0, #16 @ IRQ number
+ mov r1, sp
+ @ routine called with r0 = irq number, r1 = struct pt_regs *
+ bl asm_do_IRQ
+
+ @
+ @ Check for any pending work if returning to user
+ @
+ ldr lr, [sp, #S_EXCRET]
+ tst lr, #0x8 @ check the return stack
+ beq 2f @ returning to handler mode
+ get_thread_info tsk
+ ldr r1, [tsk, #TI_FLAGS]
+ tst r1, #_TIF_WORK_MASK
+ beq 2f @ no work pending
+ ldr r1, =0xe000ed04 @ ICSR
+ mov r0, #1 << 28 @ ICSR.PENDSVSET
+ str r0, [r1] @ raise PendSV
+
+2:
+ v7m_exception_fast_exit
+ENDPROC(__irq_entry)
+
+__pendsv_entry:
+ v7m_exception_entry
+
+ ldr r1, =0xe000ed04 @ ICSR
+ mov r0, #1 << 27 @ ICSR.PENDSVCLR
+ str r0, [r1] @ clear PendSV
+
+ @ execute the pending work, including reschedule
+ get_thread_info tsk
+ mov why, #0
+ b ret_to_user
+ENDPROC(__pendsv_entry)
+
+/*
+ * Register switch for ARMv7-M processors.
+ * r0 = previous task_struct, r1 = previous thread_info, r2 = next thread_info
+ * previous and next are guaranteed not to be the same.
+ */
+ENTRY(__switch_to)
+ .fnstart
+ .cantunwind
+ add ip, r1, #TI_CPU_SAVE
+ stmia ip!, {r4 - r11} @ Store most regs on stack
+ str sp, [ip], #4
+ str lr, [ip], #4
+ mov r5, r0
+ add r4, r2, #TI_CPU_SAVE
+ ldr r0, =thread_notify_head
+ mov r1, #THREAD_NOTIFY_SWITCH
+ bl atomic_notifier_call_chain
+ mov ip, r4
+ mov r0, r5
+ ldmia ip!, {r4 - r11} @ Load all regs saved previously
+ ldr sp, [ip], #4
+ ldr pc, [ip]
+ .fnend
+ENDPROC(__switch_to)
+
+ .data
+ .align 8
+/*
+ * Vector table (64 words => 256 bytes natural alignment)
+ */
+ENTRY(vector_table)
+ .long 0 @ 0 - Reset stack pointer
+ .long __invalid_entry @ 1 - Reset
+ .long __invalid_entry @ 2 - NMI
+ .long __invalid_entry @ 3 - HardFault
+ .long __invalid_entry @ 4 - MemManage
+ .long __invalid_entry @ 5 - BusFault
+ .long __invalid_entry @ 6 - UsageFault
+ .long __invalid_entry @ 7 - Reserved
+ .long __invalid_entry @ 8 - Reserved
+ .long __invalid_entry @ 9 - Reserved
+ .long __invalid_entry @ 10 - Reserved
+ .long vector_swi @ 11 - SVCall
+ .long __invalid_entry @ 12 - Debug Monitor
+ .long __invalid_entry @ 13 - Reserved
+ .long __pendsv_entry @ 14 - PendSV
+ .long __invalid_entry @ 15 - SysTick
+ .rept 64 - 16
+ .long __irq_entry @ 16..64 - External Interrupts
+ .endr
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 971d65c..bdccb8f 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -452,7 +452,11 @@ asm( ".pushsection .text\n"
#ifdef CONFIG_TRACE_IRQFLAGS
" bl trace_hardirqs_on\n"
#endif
+#ifdef CONFIG_CPU_V7M
+" msr primask, r7\n"
+#else
" msr cpsr_c, r7\n"
+#endif
" mov r0, r4\n"
" mov lr, r6\n"
" mov pc, r5\n"
@@ -491,6 +495,10 @@ pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
regs.ARM_r7 = SVC_MODE | PSR_ENDSTATE | PSR_ISETSTATE;
regs.ARM_pc = (unsigned long)kernel_thread_helper;
regs.ARM_cpsr = regs.ARM_r7 | PSR_I_BIT;
+#ifdef CONFIG_CPU_V7M
+ /* Return to Handler mode */
+ regs.ARM_EXCRET = 0xfffffff1L;
+#endif
return do_fork(flags|CLONE_VM|CLONE_UNTRACED, 0, ®s, 0, NULL, NULL);
}
--
1.7.9.1
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