[PATCH 10/27] objtool: Add ANNOTATE_IGNORE_NORETURN()

[Josh Poimboeuf]

A generic interface may be noreturn in one arch and returnable in
another, in which case its common declaration can't say __noreturn.

Rust has a similar issue where a few core library calls to returnable
functions are replaced after compilation with calls to a noreturn panic
function.

Add an annotation which tells objtool to ignore the noreturn status of a
given function.

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 include/linux/annotate.h            |  7 +++++++
 include/linux/objtool_types.h       |  1 +
 tools/include/linux/objtool_types.h |  1 +
 tools/objtool/check.c               | 19 +++++++++++++++++++
 tools/objtool/include/objtool/elf.h |  1 +
 5 files changed, 29 insertions(+)

diff --git a/include/linux/annotate.h b/include/linux/annotate.h
index 2f1599c9e5732..a81ca04b4c501 100644
--- a/include/linux/annotate.h
+++ b/include/linux/annotate.h
@@ -3,6 +3,7 @@
 #define _LINUX_ANNOTATE_H
 
 #include <linux/objtool_types.h>
+#include <linux/stringify.h>
 
 #ifdef CONFIG_OBJTOOL
 
@@ -105,6 +106,12 @@
  */
 #define ANNOTATE_NOCFI_SYM(sym)		asm(ASM_ANNOTATE_LABEL(sym, ANNOTYPE_NOCFI))
 
+/*
+ * Treat a function as returnable by its callers despite objtool classifying it
+ * as noreturn.
+ */
+#define ANNOTATE_IGNORE_NORETURN(sym)	asm(ASM_ANNOTATE_LABEL(sym, ANNOTYPE_IGNORE_NORETURN))
+
 /*
  * Annotate a special section entry.  This emables livepatch module generation
  * to find and extract individual special section entries as needed.
diff --git a/include/linux/objtool_types.h b/include/linux/objtool_types.h
index c24e9ea392696..ce08ecc808c67 100644
--- a/include/linux/objtool_types.h
+++ b/include/linux/objtool_types.h
@@ -66,6 +66,7 @@ struct unwind_hint {
 #define ANNOTYPE_INTRA_FUNCTION_CALL	7
 #define ANNOTYPE_REACHABLE		8
 #define ANNOTYPE_NOCFI			9
+#define ANNOTYPE_IGNORE_NORETURN	10
 
 #define ANNOTYPE_DATA_SPECIAL		1
 
diff --git a/tools/include/linux/objtool_types.h b/tools/include/linux/objtool_types.h
index c24e9ea392696..ce08ecc808c67 100644
--- a/tools/include/linux/objtool_types.h
+++ b/tools/include/linux/objtool_types.h
@@ -66,6 +66,7 @@ struct unwind_hint {
 #define ANNOTYPE_INTRA_FUNCTION_CALL	7
 #define ANNOTYPE_REACHABLE		8
 #define ANNOTYPE_NOCFI			9
+#define ANNOTYPE_IGNORE_NORETURN	10
 
 #define ANNOTYPE_DATA_SPECIAL		1
 
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 7333b0ed86818..ddb8dbe7f71d9 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -246,6 +246,9 @@ static bool is_noreturn(struct symbol *func)
 {
 	func = func->alias->pfunc;
 
+	if (func->ignore_noreturn)
+		return false;
+
 	if (is_listed_noreturn(func))
 		return true;
 
@@ -2389,6 +2392,18 @@ static int __annotate_early(struct objtool_file *file, int type, struct instruct
 		insn->noendbr = 1;
 		break;
 
+	/* Must be before detect_noreturns() */
+	case ANNOTYPE_IGNORE_NORETURN: {
+		struct symbol *sym = insn_sym(insn);
+
+		if (!sym) {
+			ERROR_INSN(insn, "dodgy IGNORE_NORETURN annotation");
+			return -1;
+		}
+		sym->ignore_noreturn = 1;
+		break;
+	}
+
 	default:
 		break;
 	}
@@ -2435,6 +2450,10 @@ static int __annotate_late(struct objtool_file *file, int type, struct instructi
 		/* early */
 		break;
 
+	case ANNOTYPE_IGNORE_NORETURN:
+		/* early */
+		break;
+
 	case ANNOTYPE_RETPOLINE_SAFE:
 		if (insn->type != INSN_JUMP_DYNAMIC &&
 		    insn->type != INSN_CALL_DYNAMIC &&
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index 46fb2230ca743..0e3593d993ac8 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -99,6 +99,7 @@ struct symbol {
 	u8 dont_correlate    : 1;
 	u8 fake		     : 1;
 	u8 _noreturn         : 1;
+	u8 ignore_noreturn   : 1;
 	struct list_head pv_target;
 	struct reloc *relocs;
 	struct section *group_sec;
-- 
2.55.0