objtool: Fix retpoline detection in asm code

The JMP_NOSPEC macro branches to __x86_retpoline_*() rather than the
__x86_indirect_thunk_*() wrappers used by C code.  Detect jumps to
__x86_retpoline_*() as retpoline dynamic jumps.

Presumably this doesn't trigger a user-visible bug.  I only found it
when testing vmlinux.o validation.

Fixes: 39b735332c ("objtool: Detect jumps to retpoline thunks")
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/31f5833e2e4f01e3d755889ac77e3661e906c09f.1611263461.git.jpoimboe@redhat.com

tools/objtool/arch/x86/special.c

@@ -48,7 +48,7 @@ bool arch_support_alt_relocation(struct special_alt *special_alt,
 	 * replacement group.
 	 */
 	return insn->offset == special_alt->new_off &&
-	       (insn->type == INSN_CALL || is_static_jump(insn));
+	       (insn->type == INSN_CALL || is_jump(insn));
 }
 
 /*

tools/objtool/check.c

@@ -785,7 +785,8 @@ static int add_jump_destinations(struct objtool_file *file)
 			dest_sec = reloc->sym->sec;
 			dest_off = reloc->sym->sym.st_value +
 				   arch_dest_reloc_offset(reloc->addend);
-		} else if (strstr(reloc->sym->name, "_indirect_thunk_")) {
+		} else if (!strncmp(reloc->sym->name, "__x86_indirect_thunk_", 21) ||
+			   !strncmp(reloc->sym->name, "__x86_retpoline_", 16)) {
 			/*
 			 * Retpoline jumps are really dynamic jumps in
 			 * disguise, so convert them accordingly.

tools/objtool/include/objtool/check.h

@@ -68,6 +68,17 @@ static inline bool is_static_jump(struct instruction *insn)
 	       insn->type == INSN_JUMP_UNCONDITIONAL;
 }
 
+static inline bool is_dynamic_jump(struct instruction *insn)
+{
+	return insn->type == INSN_JUMP_DYNAMIC ||
+	       insn->type == INSN_JUMP_DYNAMIC_CONDITIONAL;
+}
+
+static inline bool is_jump(struct instruction *insn)
+{
+	return is_static_jump(insn) || is_dynamic_jump(insn);
+}
+
 struct instruction *find_insn(struct objtool_file *file,
 			      struct section *sec, unsigned long offset);