linux-kernel - [PATCH v2] kallsyms: strip ThinLTO postfix ".cfi

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Date:   Tue, 27 Jul 2021 16:06:15 +0200
From:   Padmanabha Srinivasaiah <treasure4paddy@...il.com>
To:     jeyu@...nel.org, keescook@...omium.org
Cc:     samitolvanen@...gle.com, treasure4paddy@...il.com,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Miguel Ojeda <ojeda@...nel.org>, Joe Perches <joe@...ches.com>,
        Stephen Boyd <swboyd@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: [PATCH v2] kallsyms: strip ThinLTO postfix ".cfi_jt"

Clang ThinLTO adds a postfix ".cfi_jt" to a symbols of extern functions.
For example this breaks syscall tracer that doesn't expect such postfix,
so strip out the postfix from the output.

Signed-off-by: Padmanabha Srinivasaiah <treasure4paddy@...il.com>
---
Change in v2:
  - Use existing routine in kallsyms to strip postfix ".cfi_jt" from
    extern function name.
  - Modified the commit message accordingly

 kernel/kallsyms.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 0ba87982d017..e9148626ae6c 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -166,16 +166,20 @@ static unsigned long kallsyms_sym_address(int idx)
 
 #if defined(CONFIG_CFI_CLANG) && defined(CONFIG_LTO_CLANG_THIN)
 /*
- * LLVM appends a hash to static function names when ThinLTO and CFI are
- * both enabled, i.e. foo() becomes foo$707af9a22804d33c81801f27dcfe489b.
- * This causes confusion and potentially breaks user space tools, so we
- * strip the suffix from expanded symbol names.
+ * LLVM appends a hash to static function names and just ".cfi_jt" postfix
+ * for non-static functions when both ThinLTO and CFI are enabled,
+ * i.e. for example foo() becomes foo$707af9a22804d33c81801f27dcfe489b.
+ * This causes confusion and potentially breaks user space tools and
+ * built-in components, so we strip the suffix from expanded symbol names.
  */
 static inline bool cleanup_symbol_name(char *s)
 {
 	char *res;
 
 	res = strrchr(s, '$');
+	if (!res)
+		res = strstr(s, ".cfi_jt");
+
 	if (res)
 		*res = '\0';
 
-- 
2.17.1