create-diff-object: don't mangle .rela.__patchable_function_entries

kpatch_replace_sections_syms() substitutes the object/function symbols
for the section symbol in the relocation sections. But relocations in
.rela.__patchable_function_entries can point to an instruction ouside
the function. This is because with CALL_OPS enabled, two NOPs are added
before the function entry. __patchable_function_entries needs the
address of the first NOP above the function.

We anyway generate __patchable_function_entries again in
kpatch_create_ftrace_callsite_sections() so we can skip mangling these
relocations

Signed-off-by: Puranjay Mohan <pjy@amazon.com>

Author: puranjaymohan

kpatch-build/create-diff-object.c

@@ -1645,6 +1645,13 @@ static void kpatch_replace_sections_syms(struct kpatch_elf *kelf)
 		if (!is_rela_section(relasec) || is_debug_section(relasec))
 			continue;
 
+		/*
+		 * We regenerate __patchable_function_entries from scratch so
+		 * don't bother replacing section symbols in its relasec.
+		 */
+		if (is_patchable_function_entries_section(relasec))
+			continue;
+
 		list_for_each_entry(rela, &relasec->relas, list) {
 
 			if (rela->sym->type != STT_SECTION || !rela->sym->sec)

kpatch-build/kpatch-elf.c

@@ -65,6 +65,18 @@ bool is_text_section(struct section *sec)
 		(sec->sh.sh_flags & SHF_EXECINSTR));
 }
 
+bool is_patchable_function_entries_section(struct section *sec)
+{
+	char *name;
+
+	if (is_rela_section(sec))
+		name = sec->base->name;
+	else
+		name = sec->name;
+
+	return !strcmp(name, "__patchable_function_entries");
+}
+
 bool is_debug_section(struct section *sec)
 {
 	char *name;

kpatch-build/kpatch-elf.h

@@ -139,6 +139,7 @@ struct kpatch_elf {
 char *status_str(enum status status);
 bool is_rela_section(struct section *sec);
 bool is_text_section(struct section *sec);
+bool is_patchable_function_entries_section(struct section *sec);
 bool is_debug_section(struct section *sec);
 
 struct section *find_section_by_index(struct list_head *list, unsigned int index);