objtool: Rework the elf_rebuild_reloc_section() logic

Instead of manually calling elf_rebuild_reloc_section() on sections
we've called elf_add_reloc() on, have elf_write() DTRT.

This makes it easier to add random relocations in places without
carefully tracking when we're done and need to flush what section.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/20210326151259.754213408@infradead.org

Author: Peter Zijlstra

tools/objtool/check.c

@@ -542,9 +542,6 @@ static int create_static_call_sections(struct objtool_file *file)
 		idx++;
 	}
 
-	if (elf_rebuild_reloc_section(file->elf, reloc_sec))
-		return -1;
-
 	return 0;
 }
 
@@ -614,9 +611,6 @@ static int create_mcount_loc_sections(struct objtool_file *file)
 		idx++;
 	}
 
-	if (elf_rebuild_reloc_section(file->elf, reloc_sec))
-		return -1;
-
 	return 0;
 }
 

tools/objtool/elf.c

@@ -479,6 +479,8 @@ void elf_add_reloc(struct elf *elf, struct reloc *reloc)
 
 	list_add_tail(&reloc->list, &sec->reloc_list);
 	elf_hash_add(elf->reloc_hash, &reloc->hash, reloc_hash(reloc));
+
+	sec->changed = true;
 }
 
 static int read_rel_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
@@ -558,7 +560,9 @@ static int read_relocs(struct elf *elf)
 				return -1;
 			}
 
-			elf_add_reloc(elf, reloc);
+			list_add_tail(&reloc->list, &sec->reloc_list);
+			elf_hash_add(elf->reloc_hash, &reloc->hash, reloc_hash(reloc));
+
 			nr_reloc++;
 		}
 		max_reloc = max(max_reloc, nr_reloc);
@@ -873,14 +877,11 @@ static int elf_rebuild_rela_reloc_section(struct section *sec, int nr)
 	return 0;
 }
 
-int elf_rebuild_reloc_section(struct elf *elf, struct section *sec)
+static int elf_rebuild_reloc_section(struct elf *elf, struct section *sec)
 {
 	struct reloc *reloc;
 	int nr;
 
-	sec->changed = true;
-	elf->changed = true;
-
 	nr = 0;
 	list_for_each_entry(reloc, &sec->reloc_list, list)
 		nr++;
@@ -944,9 +945,15 @@ int elf_write(struct elf *elf)
 	struct section *sec;
 	Elf_Scn *s;
 
-	/* Update section headers for changed sections: */
+	/* Update changed relocation sections and section headers: */
 	list_for_each_entry(sec, &elf->sections, list) {
 		if (sec->changed) {
+			if (sec->base &&
+			    elf_rebuild_reloc_section(elf, sec)) {
+				WARN("elf_rebuild_reloc_section");
+				return -1;
+			}
+
 			s = elf_getscn(elf->elf, sec->idx);
 			if (!s) {
 				WARN_ELF("elf_getscn");
@@ -958,6 +965,7 @@ int elf_write(struct elf *elf)
 			}
 
 			sec->changed = false;
+			elf->changed = true;
 		}
 	}
 

tools/objtool/include/objtool/elf.h

@@ -142,7 +142,6 @@ struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *se
 struct symbol *find_func_containing(struct section *sec, unsigned long offset);
 void insn_to_reloc_sym_addend(struct section *sec, unsigned long offset,
 			      struct reloc *reloc);
-int elf_rebuild_reloc_section(struct elf *elf, struct section *sec);
 
 #define for_each_sec(file, sec)						\
 	list_for_each_entry(sec, &file->elf->sections, list)

tools/objtool/orc_gen.c

@@ -254,8 +254,5 @@ int orc_create(struct objtool_file *file)
 			return -1;
 	}
 
-	if (elf_rebuild_reloc_section(file->elf, ip_rsec))
-		return -1;
-
 	return 0;
 }