powerpc/module_64: Simplify check for -mprofile-kernel ftrace relocations

For -mprofile-kernel, we need special handling when generating stubs for
ftrace calls such as _mcount(). To faciliate this, we check if a
R_PPC64_REL24 relocation is for a symbol named "_mcount()" along with
also checking the instruction sequence. The latter is not really
required since "_mcount()" is an exported symbol and kernel modules
cannot use it. As such, drop the additional checking and simplify the
code. This helps unify stub creation for ftrace stubs with
-mprofile-kernel and aids in code reuse.

Also rename is_mprofile_mcount_callsite() to is_mprofile_ftrace_call()
to reflect the checking being done.
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/7d9c316adfa1fb787ad268bb4691e7e4059ff2d5.1587488954.git.naveen.n.rao@linux.vnet.ibm.com

arch/powerpc/kernel/module_64.c

@@ -400,19 +400,9 @@ static unsigned long stub_for_addr(const Elf64_Shdr *sechdrs,
 }
 
 #ifdef CONFIG_MPROFILE_KERNEL
-static bool is_mprofile_mcount_callsite(const char *name, u32 *instruction)
+static bool is_mprofile_ftrace_call(const char *name)
 {
-	if (strcmp("_mcount", name))
-		return false;
-
-	/*
-	 * Check if this is one of the -mprofile-kernel sequences.
-	 */
-	if (instruction[-1] == PPC_INST_STD_LR &&
-	    instruction[-2] == PPC_INST_MFLR)
-		return true;
-
-	if (instruction[-1] == PPC_INST_MFLR)
+	if (!strcmp("_mcount", name))
 		return true;
 
 	return false;
@@ -436,7 +426,7 @@ static void squash_toc_save_inst(const char *name, unsigned long addr)
 #else
 static void squash_toc_save_inst(const char *name, unsigned long addr) { }
 
-static bool is_mprofile_mcount_callsite(const char *name, u32 *instruction)
+static bool is_mprofile_ftrace_call(const char *name)
 {
 	return false;
 }
@@ -448,7 +438,7 @@ static int restore_r2(const char *name, u32 *instruction, struct module *me)
 {
 	u32 *prev_insn = instruction - 1;
 
-	if (is_mprofile_mcount_callsite(name, prev_insn))
+	if (is_mprofile_ftrace_call(name))
 		return 1;
 
 	/*