sh: Fix PC adjustments for varying opcode length.

There are a few different cases for figuring out how to
size the instruction. We read in the instruction located
at regs->pc - 4 when rewinding the opcode to figure out if
there's a 32-bit opcode before the faulting instruction, with
a default of a - 2 adjustment on a mismatch. In practice this
works for the cases where pc - 4 is just another 16-bit opcode,
or we happen to have a 32-bit and a 16-bit immediately
preceeding the pc value.

In the cases where we aren't rewinding, this is much less ugly..

We also don't bother fixing up the places where we're explicitly
dealing with 16-bit instructions, since this might lead to
confusion regarding the encoding size possibilities on other
CPU variants.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/kernel/cpu/sh4/fpu.c

@@ -16,6 +16,7 @@
 #include <linux/sched.h>
 #include <linux/signal.h>
 #include <asm/processor.h>
+#include <asm/system.h>
 #include <asm/io.h>
 
 /* The PR (precision) bit in the FP Status Register must be clear when
@@ -265,7 +266,7 @@ ieee_fpe_handler (struct pt_regs *regs)
 		nextpc = regs->pr;
 		finsn = *(unsigned short *) (regs->pc + 2);
 	} else {
-		nextpc = regs->pc + 2;
+		nextpc = regs->pc + instruction_size(insn);
 		finsn = insn;
 	}
 

arch/sh/kernel/kgdb_stub.c

@@ -867,7 +867,7 @@ static void kgdb_command_loop(const int excep_code, const int trapa_value)
 	   trap 0xff, since that indicates a compiled-in breakpoint which
 	   will not be replaced (and we would retake the trap forever) */
 	if ((excep_code == TRAP_VEC) && (trapa_value != (0x3c << 2)))
-		trap_registers.pc -= instruction_size(trap_registers.pc);
+		trap_registers.pc -= 2;
 
 	/* Undo any stepping we may have done */
 	undo_single_step();

arch/sh/kernel/process.c

@@ -498,7 +498,7 @@ asmlinkage void debug_trap_handler(unsigned long r4, unsigned long r5,
 	struct pt_regs *regs = RELOC_HIDE(&__regs, 0);
 
 	/* Rewind */
-	regs->pc -= instruction_size(regs->pc);
+	regs->pc -= instruction_size(ctrl_inw(regs->pc - 4));
 
 	if (notify_die(DIE_TRAP, regs, regs->tra & 0xff,
 		       SIGTRAP) == NOTIFY_STOP)
@@ -517,7 +517,7 @@ asmlinkage void bug_trap_handler(unsigned long r4, unsigned long r5,
 	struct pt_regs *regs = RELOC_HIDE(&__regs, 0);
 
 	/* Rewind */
-	regs->pc -= instruction_size(regs->pc);
+	regs->pc -= instruction_size(ctrl_inw(regs->pc - 4));
 
 	if (notify_die(DIE_TRAP, regs, TRAPA_BUG_OPCODE & 0xff,
 		       SIGTRAP) == NOTIFY_STOP)

arch/sh/kernel/signal.c

@@ -500,7 +500,9 @@ handle_signal(unsigned long sig, struct k_sigaction *ka, siginfo_t *info,
 				}
 			/* fallthrough */
 			case -ERESTARTNOINTR:
-				regs->pc -= instruction_size(regs->pc);
+				regs->pc -= instruction_size(
+						ctrl_inw(regs->pc - 4));
+				break;
 		}
 	} else {
 		/* gUSA handling */
@@ -516,7 +518,8 @@ handle_signal(unsigned long sig, struct k_sigaction *ka, siginfo_t *info,
 			regs->regs[15] = regs->regs[1];
 			if (regs->pc < regs->regs[0])
 				/* Go to rewind point #1 */
-				regs->pc = regs->regs[0] + offset - 2;
+				regs->pc = regs->regs[0] + offset -
+					instruction_size(ctrl_inw(regs->pc-4));
 		}
 #ifdef CONFIG_PREEMPT
 		local_irq_restore(flags);
@@ -600,9 +603,9 @@ static void do_signal(struct pt_regs *regs, unsigned int save_r0)
 		    regs->regs[0] == -ERESTARTSYS ||
 		    regs->regs[0] == -ERESTARTNOINTR) {
 			regs->regs[0] = save_r0;
-			regs->pc -= instruction_size(regs->pc);
+			regs->pc -= instruction_size(ctrl_inw(regs->pc - 4));
 		} else if (regs->regs[0] == -ERESTART_RESTARTBLOCK) {
-			regs->pc -= instruction_size(regs->pc);
+			regs->pc -= instruction_size(ctrl_inw(regs->pc - 4));
 			regs->regs[3] = __NR_restart_syscall;
 		}
 	}

arch/sh/kernel/traps.c

@@ -505,7 +505,7 @@ static int handle_unaligned_access(u16 instruction, struct pt_regs *regs)
  simple:
 	ret = handle_unaligned_ins(instruction,regs);
 	if (ret==0)
-		regs->pc += 2;
+		regs->pc += instruction_size(instruction);
 	return ret;
 }
 #endif /* CONFIG_CPU_SH2A */
@@ -682,7 +682,7 @@ asmlinkage void do_reserved_inst(unsigned long r4, unsigned long r5,
 
 	err = do_fpu_inst(inst, regs);
 	if (!err) {
-		regs->pc += 2;
+		regs->pc += instruction_size(inst);
 		return;
 	}
 	/* not a FPU inst. */