objtool: Add support for relocations without addends

Currently objtool only collects information about relocations with
addends. In recordmcount, which we are about to merge into objtool,
some supported architectures do not use rela relocations.
Signed-off-by: NMatt Helsley <mhelsley@vmware.com>
Reviewed-by: NJulien Thierry <jthierry@redhat.com>
Reviewed-by: NKamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>

tools/objtool/elf.c

@@ -496,6 +496,32 @@ void elf_add_reloc(struct elf *elf, struct reloc *reloc)
 	elf_hash_add(elf->reloc_hash, &reloc->hash, reloc_hash(reloc));
 }
 
+static int read_rel_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
+{
+	if (!gelf_getrel(sec->data, i, &reloc->rel)) {
+		WARN_ELF("gelf_getrel");
+		return -1;
+	}
+	reloc->type = GELF_R_TYPE(reloc->rel.r_info);
+	reloc->addend = 0;
+	reloc->offset = reloc->rel.r_offset;
+	*symndx = GELF_R_SYM(reloc->rel.r_info);
+	return 0;
+}
+
+static int read_rela_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
+{
+	if (!gelf_getrela(sec->data, i, &reloc->rela)) {
+		WARN_ELF("gelf_getrela");
+		return -1;
+	}
+	reloc->type = GELF_R_TYPE(reloc->rela.r_info);
+	reloc->addend = reloc->rela.r_addend;
+	reloc->offset = reloc->rela.r_offset;
+	*symndx = GELF_R_SYM(reloc->rela.r_info);
+	return 0;
+}
+
 static int read_relocs(struct elf *elf)
 {
 	struct section *sec;
@@ -505,7 +531,8 @@ static int read_relocs(struct elf *elf)
 	unsigned long nr_reloc, max_reloc = 0, tot_reloc = 0;
 
 	list_for_each_entry(sec, &elf->sections, list) {
-		if (sec->sh.sh_type != SHT_RELA)
+		if ((sec->sh.sh_type != SHT_RELA) &&
+		    (sec->sh.sh_type != SHT_REL))
 			continue;
 
 		sec->base = find_section_by_index(elf, sec->sh.sh_info);
@@ -525,16 +552,17 @@ static int read_relocs(struct elf *elf)
 				return -1;
 			}
 			memset(reloc, 0, sizeof(*reloc));
-
-			if (!gelf_getrela(sec->data, i, &reloc->rela)) {
-				WARN_ELF("gelf_getrela");
-				return -1;
+			switch (sec->sh.sh_type) {
+			case SHT_REL:
+				if (read_rel_reloc(sec, i, reloc, &symndx))
+					return -1;
+				break;
+			case SHT_RELA:
+				if (read_rela_reloc(sec, i, reloc, &symndx))
+					return -1;
+				break;
+			default: return -1;
 			}
-
-			reloc->type = GELF_R_TYPE(reloc->rela.r_info);
-			reloc->addend = reloc->rela.r_addend;
-			reloc->offset = reloc->rela.r_offset;
-			symndx = GELF_R_SYM(reloc->rela.r_info);
 			reloc->sym = find_symbol_by_index(elf, symndx);
 			reloc->sec = sec;
 			if (!reloc->sym) {
@@ -722,7 +750,37 @@ struct section *elf_create_section(struct elf *elf, const char *name,
 	return sec;
 }
 
-struct section *elf_create_reloc_section(struct elf *elf, struct section *base)
+static struct section *elf_create_rel_reloc_section(struct elf *elf, struct section *base)
+{
+	char *relocname;
+	struct section *sec;
+
+	relocname = malloc(strlen(base->name) + strlen(".rel") + 1);
+	if (!relocname) {
+		perror("malloc");
+		return NULL;
+	}
+	strcpy(relocname, ".rel");
+	strcat(relocname, base->name);
+
+	sec = elf_create_section(elf, relocname, sizeof(GElf_Rel), 0);
+	free(relocname);
+	if (!sec)
+		return NULL;
+
+	base->reloc = sec;
+	sec->base = base;
+
+	sec->sh.sh_type = SHT_REL;
+	sec->sh.sh_addralign = 8;
+	sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
+	sec->sh.sh_info = base->idx;
+	sec->sh.sh_flags = SHF_INFO_LINK;
+
+	return sec;
+}
+
+static struct section *elf_create_rela_reloc_section(struct elf *elf, struct section *base)
 {
 	char *relocname;
 	struct section *sec;
@@ -752,16 +810,53 @@ struct section *elf_create_reloc_section(struct elf *elf, struct section *base)
 	return sec;
 }
 
-int elf_rebuild_reloc_section(struct section *sec)
+struct section *elf_create_reloc_section(struct elf *elf,
+					 struct section *base,
+					 int reltype)
+{
+	switch (reltype) {
+	case SHT_REL:  return elf_create_rel_reloc_section(elf, base);
+	case SHT_RELA: return elf_create_rela_reloc_section(elf, base);
+	default:       return NULL;
+	}
+}
+
+static int elf_rebuild_rel_reloc_section(struct section *sec, int nr)
 {
 	struct reloc *reloc;
-	int nr, idx = 0, size;
-	GElf_Rela *relocs;
+	int idx = 0, size;
+	GElf_Rel *relocs;
 
-	nr = 0;
-	list_for_each_entry(reloc, &sec->reloc_list, list)
-		nr++;
+	/* Allocate a buffer for relocations */
+	size = nr * sizeof(*relocs);
+	relocs = malloc(size);
+	if (!relocs) {
+		perror("malloc");
+		return -1;
+	}
+
+	sec->data->d_buf = relocs;
+	sec->data->d_size = size;
+
+	sec->sh.sh_size = size;
+
+	idx = 0;
+	list_for_each_entry(reloc, &sec->reloc_list, list) {
+		relocs[idx].r_offset = reloc->offset;
+		relocs[idx].r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
+		idx++;
+	}
+
+	return 0;
+}
 
+static int elf_rebuild_rela_reloc_section(struct section *sec, int nr)
+{
+	struct reloc *reloc;
+	int idx = 0, size;
+	GElf_Rela *relocs;
+
+	/* Allocate a buffer for relocations with addends */
 	size = nr * sizeof(*relocs);
 	relocs = malloc(size);
 	if (!relocs) {
@@ -785,6 +880,22 @@ int elf_rebuild_reloc_section(struct section *sec)
 	return 0;
 }
 
+int elf_rebuild_reloc_section(struct section *sec)
+{
+	struct reloc *reloc;
+	int nr;
+
+	nr = 0;
+	list_for_each_entry(reloc, &sec->reloc_list, list)
+		nr++;
+
+	switch (sec->sh.sh_type) {
+	case SHT_REL:  return elf_rebuild_rel_reloc_section(sec, nr);
+	case SHT_RELA: return elf_rebuild_rela_reloc_section(sec, nr);
+	default:       return -1;
+	}
+}
+
 int elf_write(const struct elf *elf)
 {
 	struct section *sec;

tools/objtool/elf.h

@@ -61,7 +61,10 @@ struct symbol {
 struct reloc {
 	struct list_head list;
 	struct hlist_node hash;
-	GElf_Rela rela;
+	union {
+		GElf_Rela rela;
+		GElf_Rel  rel;
+	};
 	struct section *sec;
 	struct symbol *sym;
 	unsigned int type;
@@ -116,7 +119,7 @@ static inline u32 reloc_hash(struct reloc *reloc)
 
 struct elf *elf_open_read(const char *name, int flags);
 struct section *elf_create_section(struct elf *elf, const char *name, size_t entsize, int nr);
-struct section *elf_create_reloc_section(struct elf *elf, struct section *base);
+struct section *elf_create_reloc_section(struct elf *elf, struct section *base, int reltype);
 void elf_add_reloc(struct elf *elf, struct reloc *reloc);
 int elf_write(const struct elf *elf);
 void elf_close(struct elf *elf);

tools/objtool/orc_gen.c

@@ -181,7 +181,7 @@ int create_orc_sections(struct objtool_file *file)
 	if (!sec)
 		return -1;
 
-	ip_relocsec = elf_create_reloc_section(file->elf, sec);
+	ip_relocsec = elf_create_reloc_section(file->elf, sec, SHT_RELA);
 	if (!ip_relocsec)
 		return -1;