From bd2589530c713192aea7f4044a66a352a220dfe9 Mon Sep 17 00:00:00 2001
From: Artem Savkov <asavkov@redhat.com>
Date: Tue, 12 Jun 2018 16:05:30 +0200
Subject: [PATCH] create-diff-object: add symbol relations

Add a function that would detect parent/child symbol relations. So far
it only supports .cold.* symbols as children.

Signed-off-by: Artem Savkov <asavkov@redhat.com>
---
 kpatch-build/create-diff-object.c | 35 +++++++++++++++++++++++++++++++
 kpatch-build/kpatch-elf.h         |  2 ++
 2 files changed, 37 insertions(+)

diff --git a/kpatch-build/create-diff-object.c b/kpatch-build/create-diff-object.c
index d242d01..f2aca55 100644
--- a/kpatch-build/create-diff-object.c
+++ b/kpatch-build/create-diff-object.c
@@ -183,6 +183,38 @@ static void kpatch_bundle_symbols(struct kpatch_elf *kelf)
 	}
 }
 
+/*
+ * During optimization gcc may move unlikely execution branches into *.cold
+ * subfunctions. kpatch_detect_child_functions detects such subfunctions and
+ * crossreferences them with their parent functions through parent/child
+ * pointers.
+ */
+static void kpatch_detect_child_functions(struct kpatch_elf *kelf)
+{
+	struct symbol *sym;
+
+	list_for_each_entry(sym, &kelf->symbols, list) {
+		char *coldstr;
+
+		coldstr = strstr(sym->name, ".cold.");
+		if (coldstr != NULL) {
+			char *pname;
+
+			pname = strndup(sym->name, coldstr - sym->name);
+			if (!pname)
+				ERROR("strndup");
+
+			sym->parent = find_symbol_by_name(&kelf->symbols, pname);
+			free(pname);
+
+			if (!sym->parent)
+				ERROR("failed to find parent function for %s", sym->name);
+
+			sym->parent->child = sym;
+		}
+	}
+}
+
 /*
  * This function detects whether the given symbol is a "special" static local
  * variable (for lack of a better term).
@@ -3163,6 +3195,9 @@ int main(int argc, char *argv[])
 	kpatch_bundle_symbols(kelf_base);
 	kpatch_bundle_symbols(kelf_patched);
 
+	kpatch_detect_child_functions(kelf_base);
+	kpatch_detect_child_functions(kelf_patched);
+
 	kpatch_compare_elf_headers(kelf_base->elf, kelf_patched->elf);
 	kpatch_check_program_headers(kelf_base->elf);
 	kpatch_check_program_headers(kelf_patched->elf);
diff --git a/kpatch-build/kpatch-elf.h b/kpatch-build/kpatch-elf.h
index bec6398..590aa6c 100644
--- a/kpatch-build/kpatch-elf.h
+++ b/kpatch-build/kpatch-elf.h
@@ -70,6 +70,8 @@ struct section {
 struct symbol {
 	struct list_head list;
 	struct symbol *twin;
+	struct symbol *parent;
+	struct symbol *child;
 	struct section *sec;
 	GElf_Sym sym;
 	char *name;