kpatch-build: Add sym->has_func_profiling support for aarch64

The "has_function_profiling" support field in the symbol struct is used to show
that a function symbol is able to be patched. This is necessary to check that
functions which need to be patched are able to be.

On arm64 this means the presence of 2 NOP instructions at function entry
which are patched by ftrace to call the ftrace handling code. These 2 NOPs
are inserted by the compiler and the location of them is recorded in a
section called "__patchable_function_entries". Check whether a symbol has a
corresponding entry in the "__patchable_function_entries" section and if so
mark it as "has_func_profiling".

Signed-off-by: Suraj Jitindar Singh <surajjs@amazon.com>

---

V1->V2:
 - Make error message standard across architectures when no patchable entry
 - Don't store __patchable_function_entries section in
   kpatch_find_func_profiling_calls(), instead find it each time

kpatch-build/create-diff-object.c

@@ -1696,7 +1696,7 @@ static void kpatch_check_func_profiling_calls(struct kpatch_elf *kelf)
 		    (sym->parent && sym->parent->status == CHANGED))
 			continue;
 		if (!sym->twin->has_func_profiling) {
-			log_normal("function %s has no fentry/mcount call, unable to patch\n",
+			log_normal("function %s doesn't have patchable function entry, unable to patch\n",
 				   sym->name);
 			errs++;
 		}
@@ -3976,6 +3976,24 @@ static void kpatch_find_func_profiling_calls(struct kpatch_elf *kelf)
 			continue;
 
 		switch(kelf->arch) {
+		case AARCH64: {
+			struct section *sec = find_section_by_name(&kelf->sections,
+					      "__patchable_function_entries");
+			/*
+			 * If we can't find the __patchable_function_entries section or
+			 * there are no relocations in it then not patchable.
+			 */
+			if (!sec || !sec->rela)
+				return;
+			list_for_each_entry(rela, &sec->rela->relas, list) {
+				if (rela->sym->sec && sym->sec == rela->sym->sec) {
+					sym->has_func_profiling = 1;
+					break;
+				}
+			}
+
+			break;
+		}
 		case PPC64:
 			list_for_each_entry(rela, &sym->sec->rela->relas, list) {
 				if (!strcmp(rela->sym->name, "_mcount")) {

kpatch-build/kpatch-elf.c

@@ -604,6 +604,9 @@ struct kpatch_elf *kpatch_elf_open(const char *name)
 	if (!gelf_getehdr(kelf->elf, &ehdr))
 		ERROR("gelf_getehdr");
 	switch (ehdr.e_machine) {
+	case EM_AARCH64:
+		kelf->arch = AARCH64;
+		break;
 	case EM_PPC64:
 		kelf->arch = PPC64;
 		break;

kpatch-build/kpatch-elf.h

@@ -115,6 +115,7 @@ enum architecture {
 	PPC64  = 0x1 << 0,
 	X86_64 = 0x1 << 1,
 	S390   = 0x1 << 2,
+	AARCH64 = 0x1 << 3,
 };
 
 struct kpatch_elf {