compel: Fix ppc64le parasite stack layout

The ppc64le ABI allows functions to store data in caller frames.
When initializing the stack pointer prior to executing parasite code
we need to pre-allocating the minimum sized stack frame before
jumping to the parasite code.

Signed-off-by: Younes Manton <ymanton@ca.ibm.com>

compel/arch/ppc64/src/lib/include/uapi/asm/sigframe.h

@@ -23,6 +23,11 @@
 
 /* Copied from the Linux kernel header arch/powerpc/include/asm/ptrace.h */
 #define USER_REDZONE_SIZE 512
+#if _CALL_ELF != 2
+#error Only supporting ABIv2.
+#else
+#define STACK_FRAME_MIN_SIZE 32
+#endif
 
 /* Copied from the Linux kernel source file arch/powerpc/kernel/signal_64.c */
 #define TRAMP_SIZE 6

compel/arch/ppc64/src/lib/infect.c

@@ -441,13 +441,13 @@ void *remote_mmap(struct parasite_ctl *ctl, void *addr, size_t length, int prot,
 void parasite_setup_regs(unsigned long new_ip, void *stack, user_regs_struct_t *regs)
 {
 	/*
-	 * OpenPOWER ABI requires that r12 is set to the calling function addressi
+	 * OpenPOWER ABI requires that r12 is set to the calling function address
 	 * to compute the TOC pointer.
 	 */
 	regs->gpr[12] = new_ip;
 	regs->nip = new_ip;
 	if (stack)
-		regs->gpr[1] = (unsigned long)stack;
+		regs->gpr[1] = (unsigned long)stack - STACK_FRAME_MIN_SIZE;
 	regs->trap = 0;
 }