[PATCH] powerpc: Implement PR_[GS]ET_UNALIGN prctls for powerpc

This gives the ability to control whether alignment exceptions get
fixed up or reported to the process as a SIGBUS, using the existing
PR_SET_UNALIGN and PR_GET_UNALIGN prctls.  We do not implement the
option of logging a message on alignment exceptions.
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/process.c

@@ -752,6 +752,17 @@ int get_endian(struct task_struct *tsk, unsigned long adr)
 	return put_user(val, (unsigned int __user *)adr);
 }
 
+int set_unalign_ctl(struct task_struct *tsk, unsigned int val)
+{
+	tsk->thread.align_ctl = val;
+	return 0;
+}
+
+int get_unalign_ctl(struct task_struct *tsk, unsigned long adr)
+{
+	return put_user(tsk->thread.align_ctl, (unsigned int __user *)adr);
+}
+
 #define TRUNC_PTR(x)	((typeof(x))(((unsigned long)(x)) & 0xffffffff))
 
 int sys_clone(unsigned long clone_flags, unsigned long usp,

arch/powerpc/kernel/traps.c

@@ -805,9 +805,11 @@ void __kprobes program_check_exception(struct pt_regs *regs)
 
 void alignment_exception(struct pt_regs *regs)
 {
-	int fixed;
+	int fixed = 0;
 
-	fixed = fix_alignment(regs);
+	/* we don't implement logging of alignment exceptions */
+	if (!(current->thread.align_ctl & PR_UNALIGN_SIGBUS))
+		fixed = fix_alignment(regs);
 
 	if (fixed == 1) {
 		regs->nip += 4;	/* skip over emulated instruction */

include/asm-powerpc/processor.h

@@ -149,6 +149,7 @@ struct thread_struct {
 		unsigned int val;	/* Floating point status */
 	} fpscr;
 	int		fpexc_mode;	/* floating-point exception mode */
+	unsigned int	align_ctl;	/* alignment handling control */
 #ifdef CONFIG_PPC64
 	unsigned long	start_tb;	/* Start purr when proc switched in */
 	unsigned long	accum_tb;	/* Total accumilated purr for process */
@@ -217,6 +218,12 @@ extern int set_fpexc_mode(struct task_struct *tsk, unsigned int val);
 extern int get_endian(struct task_struct *tsk, unsigned long adr);
 extern int set_endian(struct task_struct *tsk, unsigned int val);
 
+#define GET_UNALIGN_CTL(tsk, adr)	get_unalign_ctl((tsk), (adr))
+#define SET_UNALIGN_CTL(tsk, val)	set_unalign_ctl((tsk), (val))
+
+extern int get_unalign_ctl(struct task_struct *tsk, unsigned long adr);
+extern int set_unalign_ctl(struct task_struct *tsk, unsigned int val);
+
 static inline unsigned int __unpack_fe01(unsigned long msr_bits)
 {
 	return ((msr_bits & MSR_FE0) >> 10) | ((msr_bits & MSR_FE1) >> 8);