powerpc/inst: Define ppc_inst_t as u32 on PPC32

Unlike PPC64 ABI, PPC32 uses the stack to pass a parameter defined
as a struct, even when the struct has a single simple element.

To avoid that, define ppc_inst_t as u32 on PPC32.

Keep it as 'struct ppc_inst' when __CHECKER__ is defined so that
sparse can perform type checking.

Also revert commit 511eea5e ("powerpc/kprobes: Fix Oops by passing
ppc_inst as a pointer to emulate_step() on ppc32") as now the
instruction to be emulated is passed as a register to emulate_step().
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/c6d0c46f598f76ad0b0a88bc0d84773bd921b17c.1638208156.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/inst.h

@@ -34,6 +34,7 @@
  * Instruction data type for POWER
  */
 
+#if defined(CONFIG_PPC64) || defined(__CHECKER__)
 typedef struct {
 	u32 val;
 #ifdef CONFIG_PPC64
@@ -46,13 +47,23 @@ static inline u32 ppc_inst_val(ppc_inst_t x)
 	return x.val;
 }
 
+#define ppc_inst(x) ((ppc_inst_t){ .val = (x) })
+
+#else
+typedef u32 ppc_inst_t;
+
+static inline u32 ppc_inst_val(ppc_inst_t x)
+{
+	return x;
+}
+#define ppc_inst(x) (x)
+#endif
+
 static inline int ppc_inst_primary_opcode(ppc_inst_t x)
 {
 	return ppc_inst_val(x) >> 26;
 }
 
-#define ppc_inst(x) ((ppc_inst_t){ .val = (x) })
-
 #ifdef CONFIG_PPC64
 #define ppc_inst_prefix(x, y) ((ppc_inst_t){ .val = (x), .suffix = (y) })
 

arch/powerpc/kernel/optprobes.c

@@ -228,12 +228,8 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
 	/*
 	 * 3. load instruction to be emulated into relevant register, and
 	 */
-	if (IS_ENABLED(CONFIG_PPC64)) {
-		temp = ppc_inst_read(p->ainsn.insn);
-		patch_imm_load_insns(ppc_inst_as_ulong(temp), 4, buff + TMPL_INSN_IDX);
-	} else {
-		patch_imm_load_insns((unsigned long)p->ainsn.insn, 4, buff + TMPL_INSN_IDX);
-	}
+	temp = ppc_inst_read(p->ainsn.insn);
+	patch_imm_load_insns(ppc_inst_as_ulong(temp), 4, buff + TMPL_INSN_IDX);
 
 	/*
 	 * 4. branch back from trampoline