[PATCH 2/7] create-diff-object: add symbol relations

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

From: Artem Savkov <asavkov@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 common.h             |  2 ++
 create-diff-object.c | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/common.h b/common.h
index 5ff9ef6ca8e9..7f3a82ffdb29 100644
--- a/common.h
+++ b/common.h
@@ -85,6 +85,8 @@ 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;
diff --git a/create-diff-object.c b/create-diff-object.c
index fed360a9aa68..b041d94d9723 100644
--- a/create-diff-object.c
+++ b/create-diff-object.c
@@ -327,6 +327,38 @@ static void kpatch_rename_mangled_functions(struct 
kpatch_elf *base,
        }
 }
 
+/*
+ * 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).
@@ -2329,6 +2361,9 @@ int main(int argc, char *argv[])
        log_debug("Open patched\n");
        kelf_patched = kpatch_elf_open(arguments.args[1]);
 
+       kpatch_detect_child_functions(kelf_base);
+       kpatch_detect_child_functions(kelf_patched);
+
        log_debug("Compare elf headers\n");
        kpatch_compare_elf_headers(kelf_base->elf, kelf_patched->elf);
        log_debug("Check program headers of base\n");
-- 
2.46.0