From b502e5b1cc29ef9ce23d0a93d8e212de8b82d51c Mon Sep 17 00:00:00 2001
From: Julien Thierry <jthierry@redhat.com>
Date: Mon, 16 Sep 2019 11:57:05 +0100
Subject: [PATCH] kpatch-build: Allow function to have multiple child functions

A symbol associated to a function can be split into multiple
sub-functions. Currently, kpatch only supports one child per function.

Extend this to support an arbitrary number of sub-function per function.

Signed-off-by: Julien Thierry <jthierry@redhat.com>
---
 kpatch-build/create-diff-object.c | 46 +++++++++++++++++++++++++------
 kpatch-build/kpatch-elf.c         |  2 ++
 kpatch-build/kpatch-elf.h         |  3 +-
 3 files changed, 42 insertions(+), 9 deletions(-)

diff --git a/kpatch-build/create-diff-object.c b/kpatch-build/create-diff-object.c
index 243af93..5f33fd6 100644
--- a/kpatch-build/create-diff-object.c
+++ b/kpatch-build/create-diff-object.c
@@ -221,6 +221,7 @@ static void kpatch_detect_child_functions(struct kpatch_elf *kelf)
 
 	list_for_each_entry(sym, &kelf->symbols, list) {
 		char *coldstr;
+		struct symbol *parent;
 
 		coldstr = strstr(sym->name, ".cold.");
 		if (coldstr != NULL) {
@@ -230,13 +231,14 @@ static void kpatch_detect_child_functions(struct kpatch_elf *kelf)
 			if (!pname)
 				ERROR("strndup");
 
-			sym->parent = find_symbol_by_name(&kelf->symbols, pname);
+			parent = find_symbol_by_name(&kelf->symbols, pname);
 			free(pname);
 
-			if (!sym->parent)
+			if (!parent)
 				ERROR("failed to find parent function for %s", sym->name);
 
-			sym->parent->child = sym;
+			list_add_tail(&sym->subfunction_node, &parent->children);
+			sym->parent = parent;
 		}
 	}
 }
@@ -659,6 +661,26 @@ static int kpatch_line_macro_change_only(struct section *sec)
 }
 #endif
 
+/*
+ * Child functions with "*.cold" names don't have _fentry_ calls, but "*.part",
+ * often do. In the later case, it is not necessary to include the parent
+ * in the output object when the child function has changed.
+ */
+static bool kpatch_changed_child_needs_parent_profiling(struct symbol *sym)
+{
+	struct symbol *child;
+
+	list_for_each_entry(child, &sym->children, subfunction_node) {
+		if (child->has_func_profiling)
+			continue;
+		if (child->sec->status == CHANGED ||
+		    kpatch_changed_child_needs_parent_profiling(child))
+			return true;
+	}
+
+	return false;
+}
+
 static void kpatch_compare_sections(struct list_head *seclist)
 {
 	struct section *sec;
@@ -691,9 +713,8 @@ static void kpatch_compare_sections(struct list_head *seclist)
 			if (sym && sym->status != CHANGED)
 				sym->status = sec->status;
 
-			if (sym && sym->child && sym->status == SAME &&
-			    sym->child->sec->status == CHANGED &&
-			    !sym->child->has_func_profiling)
+			if (sym && sym->status == SAME &&
+			    kpatch_changed_child_needs_parent_profiling(sym))
 				sym->status = CHANGED;
 		}
 	}
@@ -2364,6 +2385,16 @@ static void kpatch_mark_ignored_sections_same(struct kpatch_elf *kelf)
 			sym->status = SAME;
 }
 
+static void kpatch_mark_ignored_children_same(struct symbol *sym)
+{
+	struct symbol *child;
+
+	list_for_each_entry(child, &sym->children, subfunction_node) {
+		child->status = SAME;
+		kpatch_mark_ignored_children_same(child);
+	}
+}
+
 static void kpatch_mark_ignored_functions_same(struct kpatch_elf *kelf)
 {
 	struct section *sec;
@@ -2385,8 +2416,7 @@ static void kpatch_mark_ignored_functions_same(struct kpatch_elf *kelf)
 		rela->sym->status = SAME;
 		rela->sym->sec->status = SAME;
 
-		if (rela->sym->child)
-			rela->sym->child->status = SAME;
+		kpatch_mark_ignored_children_same(rela->sym);
 
 		if (rela->sym->sec->secsym)
 			rela->sym->sec->secsym->status = SAME;
diff --git a/kpatch-build/kpatch-elf.c b/kpatch-build/kpatch-elf.c
index c6af59e..377dc7f 100644
--- a/kpatch-build/kpatch-elf.c
+++ b/kpatch-build/kpatch-elf.c
@@ -277,6 +277,8 @@ void kpatch_create_symbol_list(struct kpatch_elf *kelf)
 	while (symbols_nr--) {
 		ALLOC_LINK(sym, &kelf->symbols);
 
+		INIT_LIST_HEAD(&sym->children);
+
 		sym->index = index;
 		if (!gelf_getsym(symtab->data, index, &sym->sym))
 			ERROR("gelf_getsym");
diff --git a/kpatch-build/kpatch-elf.h b/kpatch-build/kpatch-elf.h
index 3a0dc4b..d2bb454 100644
--- a/kpatch-build/kpatch-elf.h
+++ b/kpatch-build/kpatch-elf.h
@@ -71,7 +71,8 @@ struct symbol {
 	struct list_head list;
 	struct symbol *twin;
 	struct symbol *parent;
-	struct symbol *child;
+	struct list_head children;
+	struct list_head subfunction_node;
 	struct section *sec;
 	GElf_Sym sym;
 	char *name;