powerpc: Introduce a new helper to obtain function entry points

kprobe_lookup_name() is specific to the kprobe subsystem and may not always
return the function entry point (in a subsequent patch for KPROBES_ON_FTRACE).
For looking up function entry points, introduce a separate helper and use it
in optprobes.c

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/code-patching.h

@@ -12,6 +12,8 @@
 
 #include <asm/types.h>
 #include <asm/ppc-opcode.h>
+#include <linux/string.h>
+#include <linux/kallsyms.h>
 
 /* Flags for create_branch:
  * "b"   == create_branch(addr, target, 0);
@@ -99,6 +101,45 @@ static inline unsigned long ppc_global_function_entry(void *func)
 #endif
 }
 
+/*
+ * Wrapper around kallsyms_lookup() to return function entry address:
+ * - For ABIv1, we lookup the dot variant.
+ * - For ABIv2, we return the local entry point.
+ */
+static inline unsigned long ppc_kallsyms_lookup_name(const char *name)
+{
+	unsigned long addr;
+#ifdef PPC64_ELF_ABI_v1
+	/* check for dot variant */
+	char dot_name[1 + KSYM_NAME_LEN];
+	bool dot_appended = false;
+
+	if (strnlen(name, KSYM_NAME_LEN) >= KSYM_NAME_LEN)
+		return 0;
+
+	if (name[0] != '.') {
+		dot_name[0] = '.';
+		dot_name[1] = '\0';
+		strlcat(dot_name, name, sizeof(dot_name));
+		dot_appended = true;
+	} else {
+		dot_name[0] = '\0';
+		strlcat(dot_name, name, sizeof(dot_name));
+	}
+	addr = kallsyms_lookup_name(dot_name);
+	if (!addr && dot_appended)
+		/* Let's try the original non-dot symbol lookup	*/
+		addr = kallsyms_lookup_name(name);
+#elif defined(PPC64_ELF_ABI_v2)
+	addr = kallsyms_lookup_name(name);
+	if (addr)
+		addr = ppc_function_entry((void *)addr);
+#else
+	addr = kallsyms_lookup_name(name);
+#endif
+	return addr;
+}
+
 #ifdef CONFIG_PPC64
 /*
  * Some instruction encodings commonly used in dynamic ftracing

arch/powerpc/kernel/optprobes.c

@@ -243,10 +243,10 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
 	/*
 	 * 2. branch to optimized_callback() and emulate_step()
 	 */
-	op_callback_addr = kprobe_lookup_name("optimized_callback", 0);
-	emulate_step_addr = kprobe_lookup_name("emulate_step", 0);
+	op_callback_addr = (kprobe_opcode_t *)ppc_kallsyms_lookup_name("optimized_callback");
+	emulate_step_addr = (kprobe_opcode_t *)ppc_kallsyms_lookup_name("emulate_step");
 	if (!op_callback_addr || !emulate_step_addr) {
-		WARN(1, "kprobe_lookup_name() failed\n");
+		WARN(1, "Unable to lookup optimized_callback()/emulate_step()\n");
 		goto error;
 	}