[RFC][PATCH 3/3] objtool: Add support for relocations without addends

[Matt Helsley]

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. Since
object files use one or the other the list can be reused.

Signed-off-by: Matt Helsley <mhelsley@xxxxxxxxxx>
---
 tools/objtool/elf.c | 109 ++++++++++++++++++++++++++++++++++++--------
 tools/objtool/elf.h |   5 +-
 2 files changed, 95 insertions(+), 19 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index a162bc383945..cc7b628b1566 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -7,6 +7,7 @@
  * Copyright (C) 2014 Seth Jennings <sjenning@xxxxxxxxxx>
  */
 
+#define _GNU_SOURCE
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
@@ -490,6 +491,32 @@ 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;
@@ -497,17 +524,21 @@ static int read_relocs(struct elf *elf)
 	int i;
 	unsigned int symndx;
 	unsigned long nr_reloc, max_reloc = 0, tot_reloc = 0;
+	int (*read_reloc)(struct section *, int, struct reloc *, unsigned int *);
 
 	list_for_each_entry(sec, &elf->sections, list) {
-		if (sec->sh.sh_type != SHT_RELA)
-			continue;
+		switch(sec->sh.sh_type) {
+		case SHT_REL: read_reloc = read_rel_reloc; break;
+		case SHT_RELA: read_reloc = read_rela_reloc; break;
+		default: continue;
+		}
 
 		if (sec->sh.sh_flags & SHF_INFO_LINK) {
 			sec->base = find_section_by_index(elf, sec->sh.sh_info);
 		} else if (strncmp(sec->name, ".rel", 4) == 0) {
 			WARN("Using naming heuristic to find base of reloc section %s",
 			     sec->name);
-			sec->base = find_section_by_name(elf, sec->name + 5);
+			sec->base = find_section_by_name(elf, strchrnul(sec->name + 1, '.'));
 		}
 		if (!sec->base) {
 			WARN("can't find base section for reloc section %s",
@@ -525,16 +556,8 @@ 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");
+			if (read_reloc(sec, i, reloc, &symndx))
 				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) {
@@ -752,16 +775,50 @@ struct section *elf_create_reloc_section(struct elf *elf, struct section *base)
 	return sec;
 }
 
-int elf_rebuild_reloc_section(struct section *sec)
+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;
+
+	/*
+	 * Allocate a buffer for relocations with addends but also use
+	 * it for other relocations too. The section type determines
+	 * the size of the section, the buffer used, and the entries.
+	 */
+	size = nr * sizeof(*relocs);
+	relocs = malloc(size);
+	if (!relocs) {
+		perror("malloc");
+		return -1;
+	}
 
-	nr = 0;
-	list_for_each_entry(reloc, &sec->reloc_list, list)
-		nr++;
+	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 but also use
+	 * it for other relocations too. The section type determines
+	 * the size of the section, the buffer used, and the entries.
+	 */
 	size = nr * sizeof(*relocs);
 	relocs = malloc(size);
 	if (!relocs) {
@@ -785,6 +842,22 @@ 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;
diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h
index 6ad759fd778e..048200af8267 100644
--- a/tools/objtool/elf.h
+++ b/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;
-- 
2.20.1