From 42902d0fccd8a4889b5923aeff622681851ad68c Mon Sep 17 00:00:00 2001
From: Jessica Yu <jeyu@redhat.com>
Date: Mon, 23 Jan 2017 12:43:24 -0800
Subject: [PATCH] create-diff-object: create intermediate .kpatch.arch section

In addition to .kpatch.relocations and .kpatch.symbols, have
create-diff-object create an .kpatch.arch section. This section can be used
to create .klp.arch. sections that are required for klp modules built for
versions >= 4.9. Each entry in the .kpatch.arch section represents an
arch-specific section (.altinstructions or .parainstructions) and contains
a pointer to the arch-specific section itself (see kpatch_arch struct
member 'sec') and a pointer to the objname string (see kpatch_arch struct
member 'objname'). This is enough information to be able to build
.klp.arch. sections in a later phase of kpatch-build.
---
 kpatch-build/create-diff-object.c  | 53 ++++++++++++++++++++++++++++++
 kpatch-build/kpatch-intermediate.h |  5 +++
 2 files changed, 58 insertions(+)

diff --git a/kpatch-build/create-diff-object.c b/kpatch-build/create-diff-object.c
index 423b09e..a9b029e 100644
--- a/kpatch-build/create-diff-object.c
+++ b/kpatch-build/create-diff-object.c
@@ -1584,6 +1584,8 @@ static void kpatch_regenerate_special_section(struct kpatch_elf *kelf,
 	/* include both rela and base sections */
 	sec->include = 1;
 	sec->base->include = 1;
+	/* include secsym so .kpatch.arch relas can point to section symbols */
+	sec->base->secsym->include = 1;
 
 	/*
 	 * Update text section data buf and size.
@@ -1707,6 +1709,56 @@ static void kpatch_mark_ignored_functions_same(struct kpatch_elf *kelf)
 	}
 }
 
+static void kpatch_create_kpatch_arch_section(struct kpatch_elf *kelf, char *objname)
+{
+	struct special_section *special;
+	struct kpatch_arch *entries;
+	struct symbol *strsym;
+	struct section *sec, *karch_sec;
+	struct rela *rela;
+	int nr, index = 0;
+
+	nr = sizeof(special_sections) / sizeof(special_sections[0]);
+	karch_sec = create_section_pair(kelf, ".kpatch.arch", sizeof(*entries), nr);
+	entries = karch_sec->data->d_buf;
+
+	/* lookup strings symbol */
+	strsym = find_symbol_by_name(&kelf->symbols, ".kpatch.strings");
+	if (!strsym)
+		ERROR("can't find .kpatch.strings symbol");
+
+	for (special = special_sections; special->name; special++) {
+		if (strcmp(special->name, ".parainstructions") &&
+		    strcmp(special->name, ".altinstructions"))
+			continue;
+
+		sec = find_section_by_name(&kelf->sections, special->name);
+		if (!sec)
+			continue;
+
+		/* entries[index].sec */
+		ALLOC_LINK(rela, &karch_sec->rela->relas);
+		rela->sym = sec->secsym;
+		rela->type = R_X86_64_64;
+		rela->addend = 0;
+		rela->offset = index * sizeof(*entries) + \
+			       offsetof(struct kpatch_arch, sec);
+
+		/* entries[index].objname */
+		ALLOC_LINK(rela, &karch_sec->rela->relas);
+		rela->sym = strsym;
+		rela->type = R_X86_64_64;
+		rela->addend = offset_of_string(&kelf->strings, objname);
+		rela->offset = index * sizeof(*entries) + \
+			       offsetof(struct kpatch_arch, objname);
+
+		index++;
+	}
+
+	karch_sec->data->d_size = index * sizeof(struct kpatch_arch);
+	karch_sec->sh.sh_size = karch_sec->data->d_size;
+}
+
 static void kpatch_process_special_sections(struct kpatch_elf *kelf)
 {
 	struct special_section *special;
@@ -2462,6 +2514,7 @@ int main(int argc, char *argv[])
 	kpatch_create_strings_elements(kelf_out);
 	kpatch_create_patches_sections(kelf_out, lookup, hint, objname);
 	kpatch_create_intermediate_sections(kelf_out, lookup, hint, objname, pmod_name);
+	kpatch_create_kpatch_arch_section(kelf_out, objname);
 	kpatch_create_hooks_objname_rela(kelf_out, objname);
 	kpatch_build_strings_section_data(kelf_out);
 
diff --git a/kpatch-build/kpatch-intermediate.h b/kpatch-build/kpatch-intermediate.h
index f6ea34f..87eeff3 100644
--- a/kpatch-build/kpatch-intermediate.h
+++ b/kpatch-build/kpatch-intermediate.h
@@ -40,4 +40,9 @@ struct kpatch_relocation {
 	char *objname; /* object to which this rela applies to */
 	struct kpatch_symbol *ksym;
 };
+
+struct kpatch_arch {
+        unsigned long sec;
+        char *objname;
+};
 #endif /* _KPATCH_ELF_H_ */