objtool: Get rid of reloc->idx

Use the array offset to calculate the reloc index.

With allyesconfig + CONFIG_DEBUG_INFO:

- Before: peak heap memory consumption: 45.56G
- After:  peak heap memory consumption: 43.83G

Link: https://lore.kernel.org/r/7351d2ebad0519027db14a32f6204af84952574a.1685464332.git.jpoimboe@kernel.orgSigned-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

tools/objtool/elf.c

@@ -829,7 +829,6 @@ static struct reloc *elf_init_reloc(struct elf *elf, struct section *rsec,
 		return NULL;
 	}
 
-	reloc->idx = reloc_idx;
 	reloc->sec = rsec;
 	reloc->offset = offset;
 	reloc->type = type;
@@ -954,7 +953,6 @@ static int read_relocs(struct elf *elf)
 				return -1;
 
 			reloc->sec = rsec;
-			reloc->idx = i;
 			symndx = GELF_R_SYM(reloc->rel.r_info);
 			reloc->sym = sym = find_symbol_by_index(elf, symndx);
 			if (!reloc->sym) {
@@ -1237,9 +1235,9 @@ int elf_write_reloc(struct elf *elf, struct reloc *reloc)
 
 	if (rsec->sh.sh_type == SHT_RELA) {
 		reloc->rela.r_addend = reloc->addend;
-		ret = gelf_update_rela(rsec->data, reloc->idx, &reloc->rela);
+		ret = gelf_update_rela(rsec->data, reloc_idx(reloc), &reloc->rela);
 	} else {
-		ret = gelf_update_rel(rsec->data, reloc->idx, &reloc->rel);
+		ret = gelf_update_rel(rsec->data, reloc_idx(reloc), &reloc->rel);
 	}
 
 	if (!ret) {

tools/objtool/include/objtool/elf.h

@@ -76,9 +76,8 @@ struct reloc {
 	struct symbol *sym;
 	struct list_head sym_reloc_entry;
 	unsigned long offset;
-	unsigned int type;
 	s64 addend;
-	int idx;
+	unsigned int type;
 	bool jump_table_start;
 };
 
@@ -200,6 +199,11 @@ static inline unsigned int sec_num_entries(struct section *sec)
 	return sec->sh.sh_size / sec->sh.sh_entsize;
 }
 
+static inline unsigned int reloc_idx(struct reloc *reloc)
+{
+	return reloc - reloc->sec->relocs;
+}
+
 #define for_each_sec(file, sec)						\
 	list_for_each_entry(sec, &file->elf->sections, list)
 
@@ -219,7 +223,7 @@ static inline unsigned int sec_num_entries(struct section *sec)
 		     __i++, reloc++)
 
 #define for_each_reloc_from(rsec, reloc)				\
-	for (int __i = reloc->idx;					\
+	for (int __i = reloc_idx(reloc);				\
 	     __i < sec_num_entries(rsec);				\
 	     __i++, reloc++)