Subject: Re: linux-next: build warnings after merge of the tip tree

From: Peter Zijlstra <[email-masked]>
Date: Tue, 22 Mar 2022 11:59:04 +0100

On Tue, Mar 22, 2022 at 11:46:04AM +0100, Peter Zijlstra wrote:
> On Mon, Mar 21, 2022 at 01:55:49PM +0100, Peter Zijlstra wrote:

> > > arch/x86/crypto/poly1305-x86_64.o: warning: objtool: poly1305_blocks_avx() falls through to next function poly1305_blocks_x86_64()
> > > arch/x86/crypto/poly1305-x86_64.o: warning: objtool: poly1305_emit_avx() falls through to next function poly1305_emit_x86_64()
> > > arch/x86/crypto/poly1305-x86_64.o: warning: objtool: poly1305_blocks_avx2() falls through to next function poly1305_blocks_x86_64()
> > 
> > Yes, those are somewhere on the todo list, lemme bump them.

The poly one is a little more involved since it's a perl script writing
asm O_O

Looking at the generated asm tough, the these are conditional tail-calls
and objtool *should* recognise them but doesn't...

This seems to cure.

---
 tools/objtool/check.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 6de5085e3e5a..b848e1ddd5d8 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1239,11 +1239,20 @@ static bool same_function(struct instruction *insn1, struct instruction *insn2)
 	return insn1->func->pfunc == insn2->func->pfunc;
 }
 
-static bool is_first_func_insn(struct instruction *insn)
+static bool is_first_func_insn(struct objtool_file *file, struct instruction *insn)
 {
-	return insn->offset == insn->func->offset ||
-	       (insn->type == INSN_ENDBR &&
-		insn->offset == insn->func->offset + insn->len);
+	if (insn->offset == insn->func->offset)
+		return true;
+
+	if (ibt) {
+		struct instruction *prev = prev_insn_same_sym(file, insn);
+
+		if (prev && prev->type == INSN_ENDBR &&
+		    insn->offset == insn->func->offset + prev->len)
+			return true;
+	}
+
+	return false;
 }
 
 /*
@@ -1327,7 +1336,7 @@ static int add_jump_destinations(struct objtool_file *file)
 				insn->jump_dest->func->pfunc = insn->func;
 
 			} else if (!same_function(insn, insn->jump_dest) &&
-				   is_first_func_insn(insn->jump_dest)) {
+				   is_first_func_insn(file, insn->jump_dest)) {
 				/* internal sibling call (without reloc) */
 				add_call_dest(file, insn, insn->jump_dest->func, true);
 			}