Make undefined exception entry MPSAFE.

The old code used static storage to preserve a couple registers while
setting up the trapframe for the main handler.  Doing so was the last
leftover crumbs from the days when a low-level debugger was hooked into
the exception entry code.

Now the exception entry sequence is essentially the same as for the
other exceptions, which still involves needlessly indirecting through
a function pointer which points to the same code on every platform.
Removing that indirection will be handled as a separate cleanup.

This work is based on an analysis by Juergen Weiss.

2 files changed, 14 insertions, 36 deletions

diff --git a/sys/arm/arm/exception.S b/sys/arm/arm/exception.S
index 3d110e3..d7ef5f2 100644
--- a/sys/arm/arm/exception.S
+++ b/sys/arm/arm/exception.S
@@ -218,46 +218,25 @@ END(exception_exit)
  *	look like direct entry from the vector.
  */
 ASENTRY_NP(undefined_entry)
-	stmfd	sp!, {r0, r1}
-	ldr	r0, Lundefined_handler_indirection
-	ldr	r1, [sp], #0x0004
-	str	r1, [r0, #0x0000]
-	ldr	r1, [sp], #0x0004
-	str	r1, [r0, #0x0004]
-	ldmia	r0, {r0, r1, pc}
 
-
-Lundefined_handler_indirection:
-	.word	Lundefined_handler_indirection_data
+        sub     lr, lr, #0x00000004     /* Adjust the lr */
+	PUSHFRAMEINSVC			/* Push trap frame and switch */
+					/* to SVC32 mode */
+	ldr	r1, Lundefined_handler_address
+	adr	lr, exception_exit
+	mov	r0, sp			/* pass the stack pointer as r0 */
+	ldr	pc, [r1]
 END(undefined_entry)
 
-/*
- * assembly bounce code for calling the kernel
- * undefined instruction handler. This uses
- * a standard trap frame and is called in SVC mode.
- */
-
-ENTRY_NP(undefinedinstruction_bounce)
-	PUSHFRAMEINSVC
+ASENTRY_NP(undefinedinstruction_bounce)
+	b	undefinedinstruction
+END(undefinedinstruction_bounce)
 
-	mov	r0, sp
-	adr	lr, exception_exit
-	b	_C_LABEL(undefinedinstruction)
+Lundefined_handler_address:
+	.word	_C_LABEL(undefined_handler_address)
 
 	.data
-	.align	0
-
-/*
- * Indirection data
- * 2 words use for preserving r0 and r1
- * 3rd word contains the undefined handler address.
- */
-
-Lundefined_handler_indirection_data:
-	.word	0
-	.word	0
-
 	.global	_C_LABEL(undefined_handler_address)
 _C_LABEL(undefined_handler_address):
-	.word	_C_LABEL(undefinedinstruction_bounce)
-END(undefinedinstruction_bounce)
+	.word	undefinedinstruction_bounce
+
diff --git a/sys/arm/arm/undefined.c b/sys/arm/arm/undefined.c
index 7829ece..5b7b917 100644
--- a/sys/arm/arm/undefined.c
+++ b/sys/arm/arm/undefined.c
@@ -183,7 +183,6 @@ undefinedinstruction(struct trapframe *frame)
 	if (!(frame->tf_spsr & I32_bit))
 		enable_interrupts(I32_bit|F32_bit);
 
-	frame->tf_pc -= INSN_SIZE;
 	PCPU_INC(cnt.v_trap);
 
 	fault_pc = frame->tf_pc;