[PATCH] powerpc: Implement support for setting little-endian mode via prctl

This adds the PowerPC part of the code to allow processes to change
their endian mode via prctl.

This also extends the alignment exception handler to be able to fix up
alignment exceptions that occur in little-endian mode, both for
"PowerPC" little-endian and true little-endian.

We always enter signal handlers in big-endian mode -- the support for
little-endian mode does not amount to the creation of a little-endian
user/kernel ABI.  If the signal handler returns, the endian mode is
restored to what it was when the signal was delivered.

We have two new kernel CPU feature bits, one for PPC little-endian and
one for true little-endian.  Most of the classic 32-bit processors
support PPC little-endian, and this is reflected in the CPU feature
table.  There are two corresponding feature bits reported to userland
in the AT_HWCAP aux vector entry.

This is based on an earlier patch by Anton Blanchard.

Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 44 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 2dd47d2..2d35d83 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -708,6 +708,50 @@ int get_fpexc_mode(struct task_struct *tsk, unsigned long adr)
 	return put_user(val, (unsigned int __user *) adr);
 }
 
+int set_endian(struct task_struct *tsk, unsigned int val)
+{
+	struct pt_regs *regs = tsk->thread.regs;
+
+	if ((val == PR_ENDIAN_LITTLE && !cpu_has_feature(CPU_FTR_REAL_LE)) ||
+	    (val == PR_ENDIAN_PPC_LITTLE && !cpu_has_feature(CPU_FTR_PPC_LE)))
+		return -EINVAL;
+
+	if (regs == NULL)
+		return -EINVAL;
+
+	if (val == PR_ENDIAN_BIG)
+		regs->msr &= ~MSR_LE;
+	else if (val == PR_ENDIAN_LITTLE || val == PR_ENDIAN_PPC_LITTLE)
+		regs->msr |= MSR_LE;
+	else
+		return -EINVAL;
+
+	return 0;
+}
+
+int get_endian(struct task_struct *tsk, unsigned long adr)
+{
+	struct pt_regs *regs = tsk->thread.regs;
+	unsigned int val;
+
+	if (!cpu_has_feature(CPU_FTR_PPC_LE) &&
+	    !cpu_has_feature(CPU_FTR_REAL_LE))
+		return -EINVAL;
+
+	if (regs == NULL)
+		return -EINVAL;
+
+	if (regs->msr & MSR_LE) {
+		if (cpu_has_feature(CPU_FTR_REAL_LE))
+			val = PR_ENDIAN_LITTLE;
+		else
+			val = PR_ENDIAN_PPC_LITTLE;
+	} else
+		val = PR_ENDIAN_BIG;
+
+	return put_user(val, (unsigned int __user *)adr);
+}
+
 #define TRUNC_PTR(x)	((typeof(x))(((unsigned long)(x)) & 0xffffffff))
 
 int sys_clone(unsigned long clone_flags, unsigned long usp,