linux-kernel - [PATCH 3/3] objtool: Generate ORC data for _

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Date:   Wed, 12 Apr 2023 13:26:15 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Miroslav Benes <mbenes@...e.cz>
Subject: [PATCH 3/3] objtool: Generate ORC data for __pfx code

Allow unwinding from prefix code by copying the CFI from the starting
instruction of the corresponding function.  Even when the NOPs are
replaced, they're still stack-invariant instructions so the same ORC
entry can be reused everywhere.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 tools/objtool/check.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 2f3136145b2e..3f27a0278bf8 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -4123,6 +4123,7 @@ static bool ignore_unreachable_insn(struct objtool_file *file, struct instructio
 static int add_prefix_symbol(struct objtool_file *file, struct symbol *func)
 {
 	struct instruction *insn, *prev;
+	struct cfi_state *cfi;
 
 	insn = find_insn(file, func->sec, func->offset);
 	if (!insn)
@@ -4151,6 +4152,19 @@ static int add_prefix_symbol(struct objtool_file *file, struct symbol *func)
 	if (!prev)
 		return -1;
 
+	if (!insn->cfi) {
+		/*
+		 * This can happen if stack validation isn't enabled or the
+		 * function is annotated with STACK_FRAME_NON_STANDARD.
+		 */
+		return 0;
+	}
+
+	/* Propagate insn->cfi to the prefix code */
+	cfi = cfi_hash_find_or_add(insn->cfi);
+	for (; prev != insn; prev = next_insn_same_sec(file, prev))
+		prev->cfi = cfi;
+
 	return 0;
 }
 
@@ -4158,7 +4172,7 @@ static int add_prefix_symbols(struct objtool_file *file)
 {
 	struct section *sec;
 	struct symbol *func;
-	int ret, warnings = 0;
+	int warnings = 0;
 
 	for_each_sec(file, sec) {
 		if (!(sec->sh.sh_flags & SHF_EXECINSTR))
-- 
2.39.2