objtool: Shrink reloc->sym_reloc_entry

Convert it to a singly-linked list.

With allyesconfig + CONFIG_DEBUG_INFO:

- Before: peak heap memory consumption: 38.64G
- After:  peak heap memory consumption: 36.89G

Link: https://lore.kernel.org/r/a51f0a6f9bbf2494d5a3a449807307e78a940988.1685464332.git.jpoimboe@kernel.orgSigned-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

tools/objtool/elf.c

@@ -356,7 +356,6 @@ static void elf_add_symbol(struct elf *elf, struct symbol *sym)
 	struct rb_node *pnode;
 	struct symbol *iter;
 
-	INIT_LIST_HEAD(&sym->reloc_list);
 	INIT_LIST_HEAD(&sym->pv_target);
 	sym->alias = sym;
 
@@ -540,7 +539,7 @@ static int elf_update_sym_relocs(struct elf *elf, struct symbol *sym)
 {
 	struct reloc *reloc;
 
-	list_for_each_entry(reloc, &sym->reloc_list, sym_reloc_entry) {
+	for (reloc = sym->relocs; reloc; reloc = reloc->sym_next_reloc) {
 		reloc->rel.r_info = GELF_R_INFO(reloc->sym->idx, reloc_type(reloc));
 		if (elf_write_reloc(elf, reloc))
 			return -1;
@@ -841,8 +840,9 @@ static struct reloc *elf_init_reloc(struct elf *elf, struct section *rsec,
 	if (elf_write_reloc(elf, reloc))
 		return NULL;
 
-	list_add_tail(&reloc->sym_reloc_entry, &sym->reloc_list);
 	elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
+	reloc->sym_next_reloc = sym->relocs;
+	sym->relocs = reloc;
 
 	return reloc;
 }
@@ -960,8 +960,9 @@ static int read_relocs(struct elf *elf)
 				return -1;
 			}
 
-			list_add_tail(&reloc->sym_reloc_entry, &sym->reloc_list);
 			elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc));
+			reloc->sym_next_reloc = sym->relocs;
+			sym->relocs = reloc;
 
 			nr_reloc++;
 		}

tools/objtool/include/objtool/elf.h

@@ -63,7 +63,7 @@ struct symbol {
 	u8 profiling_func    : 1;
 	u8 warned	     : 1;
 	struct list_head pv_target;
-	struct list_head reloc_list;
+	struct reloc *relocs;
 };
 
 struct reloc {
@@ -74,7 +74,7 @@ struct reloc {
 	};
 	struct section *sec;
 	struct symbol *sym;
-	struct list_head sym_reloc_entry;
+	struct reloc *sym_next_reloc;
 };
 
 struct elf {