objtool: Convert {.UN}REACHABLE to ANNOTATE

Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/20241128094312.353431347@infradead.org

Author: Peter Zijlstra

arch/loongarch/include/asm/bug.h

@@ -45,7 +45,7 @@
 #define __WARN_FLAGS(flags)					\
 do {								\
 	instrumentation_begin();				\
-	__BUG_FLAGS(BUGFLAG_WARNING|(flags), ASM_REACHABLE);	\
+	__BUG_FLAGS(BUGFLAG_WARNING|(flags), ANNOTATE_REACHABLE);\
 	instrumentation_end();					\
 } while (0)
 

arch/x86/entry/entry_64.S

@@ -311,7 +311,7 @@ SYM_CODE_END(xen_error_entry)
 	call	\cfunc
 
 	/* For some configurations \cfunc ends up being a noreturn. */
-	REACHABLE
+	ANNOTATE_REACHABLE
 
 	jmp	error_return
 .endm
@@ -532,7 +532,7 @@ SYM_CODE_START(\asmsym)
 	call	\cfunc
 
 	/* For some configurations \cfunc ends up being a noreturn. */
-	REACHABLE
+	ANNOTATE_REACHABLE
 
 	jmp	paranoid_exit
 

arch/x86/include/asm/bug.h

@@ -92,7 +92,7 @@ do {								\
 do {								\
 	__auto_type __flags = BUGFLAG_WARNING|(flags);		\
 	instrumentation_begin();				\
-	_BUG_FLAGS(ASM_UD2, __flags, ASM_REACHABLE);		\
+	_BUG_FLAGS(ASM_UD2, __flags, ANNOTATE_REACHABLE);	\
 	instrumentation_end();					\
 } while (0)
 

arch/x86/include/asm/irq_stack.h

@@ -101,7 +101,7 @@
 
 #define ASM_CALL_ARG0							\
 	"call %c[__func]				\n"		\
-	ASM_REACHABLE
+	ANNOTATE_REACHABLE
 
 #define ASM_CALL_ARG1							\
 	"movq	%[arg1], %%rdi				\n"		\

include/linux/objtool.h

@@ -111,14 +111,6 @@
 #endif
 .endm
 
-
-.macro REACHABLE
-.Lhere_\@:
-	.pushsection .discard.reachable
-	.long	.Lhere_\@
-	.popsection
-.endm
-
 .macro ANNOTATE type:req
 .Lhere_\@:
 	.pushsection .discard.annotate_insn,"M",@progbits,8
@@ -138,14 +130,11 @@
 #define STACK_FRAME_NON_STANDARD_FP(func)
 #define __ASM_ANNOTATE(label, type)
 #define ASM_ANNOTATE(type)
-#define ASM_REACHABLE
 #else
 .macro UNWIND_HINT type:req sp_reg=0 sp_offset=0 signal=0
 .endm
 .macro STACK_FRAME_NON_STANDARD func:req
 .endm
-.macro REACHABLE
-.endm
 .macro ANNOTATE type:req
 .endm
 #endif
@@ -187,6 +176,12 @@
  * it will be ignored.
  */
 #define ANNOTATE_UNRET_BEGIN		ASM_ANNOTATE(ANNOTYPE_UNRET_BEGIN)
+/*
+ * This should be used directly after an instruction that is considered
+ * terminating, like a noreturn CALL or UD2 when we know they are not -- eg
+ * WARN using UD2.
+ */
+#define ANNOTATE_REACHABLE		ASM_ANNOTATE(ANNOTYPE_REACHABLE)
 
 #else
 #define ANNOTATE_NOENDBR		ANNOTATE type=ANNOTYPE_NOENDBR
@@ -196,6 +191,7 @@
 #define ANNOTATE_IGNORE_ALTERNATIVE	ANNOTATE type=ANNOTYPE_IGNORE_ALTS
 #define ANNOTATE_INTRA_FUNCTION_CALL	ANNOTATE type=ANNOTYPE_INTRA_FUNCTION_CALL
 #define ANNOTATE_UNRET_BEGIN		ANNOTATE type=ANNOTYPE_UNRET_BEGIN
+#define ANNOTATE_REACHABLE		ANNOTATE type=ANNOTYPE_REACHABLE
 #endif
 
 #if defined(CONFIG_NOINSTR_VALIDATION) && \

include/linux/objtool_types.h

@@ -64,5 +64,6 @@ struct unwind_hint {
 #define ANNOTYPE_UNRET_BEGIN		5
 #define ANNOTYPE_IGNORE_ALTS		6
 #define ANNOTYPE_INTRA_FUNCTION_CALL	7
+#define ANNOTYPE_REACHABLE		8
 
 #endif /* _LINUX_OBJTOOL_TYPES_H */

tools/include/linux/objtool_types.h

@@ -64,5 +64,6 @@ struct unwind_hint {
 #define ANNOTYPE_UNRET_BEGIN		5
 #define ANNOTYPE_IGNORE_ALTS		6
 #define ANNOTYPE_INTRA_FUNCTION_CALL	7
+#define ANNOTYPE_REACHABLE		8
 
 #endif /* _LINUX_OBJTOOL_TYPES_H */

tools/objtool/check.c

@@ -627,56 +627,6 @@ static struct instruction *find_last_insn(struct objtool_file *file,
 	return insn;
 }
 
-/*
- * Mark "ud2" instructions and manually annotated dead ends.
- */
-static int add_dead_ends(struct objtool_file *file)
-{
-	struct section *rsec;
-	struct reloc *reloc;
-	struct instruction *insn;
-	uint64_t offset;
-
-	/*
-	 * UD2 defaults to being a dead-end, allow them to be annotated for
-	 * non-fatal, eg WARN.
-	 */
-	rsec = find_section_by_name(file->elf, ".rela.discard.reachable");
-	if (!rsec)
-		return 0;
-
-	for_each_reloc(rsec, reloc) {
-		if (reloc->sym->type == STT_SECTION) {
-			offset = reloc_addend(reloc);
-		} else if (reloc->sym->local_label) {
-			offset = reloc->sym->offset;
-		} else {
-			WARN("unexpected relocation symbol type in %s", rsec->name);
-			return -1;
-		}
-
-		insn = find_insn(file, reloc->sym->sec, offset);
-		if (insn)
-			insn = prev_insn_same_sec(file, insn);
-		else if (offset == reloc->sym->sec->sh.sh_size) {
-			insn = find_last_insn(file, reloc->sym->sec);
-			if (!insn) {
-				WARN("can't find reachable insn at %s+0x%" PRIx64,
-				     reloc->sym->sec->name, offset);
-				return -1;
-			}
-		} else {
-			WARN("can't find reachable insn at %s+0x%" PRIx64,
-			     reloc->sym->sec->name, offset);
-			return -1;
-		}
-
-		insn->dead_end = false;
-	}
-
-	return 0;
-}
-
 static int create_static_call_sections(struct objtool_file *file)
 {
 	struct static_call_site *site;
@@ -2306,6 +2256,7 @@ static int read_annotate(struct objtool_file *file,
 	struct section *sec;
 	struct instruction *insn;
 	struct reloc *reloc;
+	uint64_t offset;
 	int type, ret;
 
 	sec = find_section_by_name(file->elf, ".discard.annotate_insn");
@@ -2327,8 +2278,19 @@ static int read_annotate(struct objtool_file *file,
 	for_each_reloc(sec->rsec, reloc) {
 		type = *(u32 *)(sec->data->d_buf + (reloc_idx(reloc) * sec->sh.sh_entsize) + 4);
 
-		insn = find_insn(file, reloc->sym->sec,
-				 reloc->sym->offset + reloc_addend(reloc));
+		offset = reloc->sym->offset + reloc_addend(reloc);
+		insn = find_insn(file, reloc->sym->sec, offset);
+
+		/*
+		 * Reachable annotations are 'funneh' and act on the previous instruction :/
+		 */
+		if (type == ANNOTYPE_REACHABLE) {
+			if (insn)
+				insn = prev_insn_same_sec(file, insn);
+			else if (offset == reloc->sym->sec->sh.sh_size)
+				insn = find_last_insn(file, reloc->sym->sec);
+		}
+
 		if (!insn) {
 			WARN("bad .discard.annotate_insn entry: %d of type %d", reloc_idx(reloc), type);
 			return -1;
@@ -2420,6 +2382,10 @@ static int __annotate_late(struct objtool_file *file, int type, struct instructi
 		insn->unret = 1;
 		break;
 
+	case ANNOTYPE_REACHABLE:
+		insn->dead_end = false;
+		break;
+
 	default:
 		break;
 	}
@@ -2566,14 +2532,6 @@ static int decode_sections(struct objtool_file *file)
 	if (ret)
 		return ret;
 
-	/*
-	 * Must be after add_call_destinations() such that it can override
-	 * dead_end_function() marks.
-	 */
-	ret = add_dead_ends(file);
-	if (ret)
-		return ret;
-
 	ret = add_jump_table_alts(file);
 	if (ret)
 		return ret;
@@ -2582,6 +2540,10 @@ static int decode_sections(struct objtool_file *file)
 	if (ret)
 		return ret;
 
+	/*
+	 * Must be after add_call_destinations() such that it can override
+	 * dead_end_function() marks.
+	 */
 	ret = read_annotate(file, __annotate_late);
 	if (ret)
 		return ret;