[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, 8 insertions, 4 deletions

diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 23ba69c26913..66a5fbe31989 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -141,9 +141,7 @@ static long restore_sigcontext(struct pt_regs *regs, sigset_t *set, int sig,
 	unsigned long err = 0;
 	unsigned long save_r13 = 0;
 	elf_greg_t *gregs = (elf_greg_t *)regs;
-#ifdef CONFIG_ALTIVEC
 	unsigned long msr;
-#endif
 	int i;
 
 	/* If this is not a signal return, we preserve the TLS in r13 */
@@ -154,7 +152,12 @@ static long restore_sigcontext(struct pt_regs *regs, sigset_t *set, int sig,
 	err |= __copy_from_user(regs, &sc->gp_regs,
 				PT_MSR*sizeof(unsigned long));
 
-	/* skip MSR and SOFTE */
+	/* get MSR separately, transfer the LE bit if doing signal return */
+	err |= __get_user(msr, &sc->gp_regs[PT_MSR]);
+	if (sig)
+		regs->msr = (regs->msr & ~MSR_LE) | (msr & MSR_LE);
+
+	/* skip SOFTE */
 	for (i = PT_MSR+1; i <= PT_RESULT; i++) {
 		if (i == PT_SOFTE)
 			continue;
@@ -179,7 +182,6 @@ static long restore_sigcontext(struct pt_regs *regs, sigset_t *set, int sig,
 
 #ifdef CONFIG_ALTIVEC
 	err |= __get_user(v_regs, &sc->v_regs);
-	err |= __get_user(msr, &sc->gp_regs[PT_MSR]);
 	if (err)
 		return err;
 	/* Copy 33 vec registers (vr0..31 and vscr) from the stack */
@@ -410,6 +412,8 @@ static int setup_rt_frame(int signr, struct k_sigaction *ka, siginfo_t *info,
 
 	/* Set up "regs" so we "return" to the signal handler. */
 	err |= get_user(regs->nip, &funct_desc_ptr->entry);
+	/* enter the signal handler in big-endian mode */
+	regs->msr &= ~MSR_LE;
 	regs->gpr[1] = newsp;
 	err |= get_user(regs->gpr[2], &funct_desc_ptr->toc);
 	regs->gpr[3] = signr;