powerpc: ELF2 binaries launched directly.

No function descriptor, but we set r12 up and set TIF_RESTOREALL as it
normally isn't restored on return from syscall.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 35 insertions, 15 deletions

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 75c2d1009985..0650e18169f8 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1086,25 +1086,45 @@ void start_thread(struct pt_regs *regs, unsigned long start, unsigned long sp)
         regs->msr = MSR_USER;
 #else
         if (!is_32bit_task()) {
-                unsigned long entry, toc;
+                unsigned long entry;
 
-                /* start is a relocated pointer to the function descriptor for
-                 * the elf _start routine.  The first entry in the function
-                 * descriptor is the entry address of _start and the second
-                 * entry is the TOC value we need to use.
-                 */
-                __get_user(entry, (unsigned long __user *)start);
-                __get_user(toc, (unsigned long __user *)start+1);
+                if (is_elf2_task()) {
+                        /* Look ma, no function descriptors! */
+                        entry = start;
 
-                /* Check whether the e_entry function descriptor entries
-                 * need to be relocated before we can use them.
-                 */
-                if (load_addr != 0) {
-                        entry += load_addr;
-                        toc   += load_addr;
+                        /*
+                         * Ulrich says:
+                         *   The latest iteration of the ABI requires that when
+                         *   calling a function (at its global entry point),
+                         *   the caller must ensure r12 holds the entry point
+                         *   address (so that the function can quickly
+                         *   establish addressability).
+                         */
+                        regs->gpr[12] = start;
+                        /* Make sure that's restored on entry to userspace. */
+                        set_thread_flag(TIF_RESTOREALL);
+                } else {
+                        unsigned long toc;
+
+                        /* start is a relocated pointer to the function
+                         * descriptor for the elf _start routine.  The first
+                         * entry in the function descriptor is the entry
+                         * address of _start and the second entry is the TOC
+                         * value we need to use.
+                         */
+                        __get_user(entry, (unsigned long __user *)start);
+                        __get_user(toc, (unsigned long __user *)start+1);
+
+                        /* Check whether the e_entry function descriptor entries
+                         * need to be relocated before we can use them.
+                         */
+                        if (load_addr != 0) {
+                                entry += load_addr;
+                                toc   += load_addr;
+                        }
+                        regs->gpr[2] = toc;
                 }
                 regs->nip = entry;
-                regs->gpr[2] = toc;
                 regs->msr = MSR_USER64;
         } else {
                 regs->nip = start;