linux-kernel - [RFC PATCH] objtool: Skip unannotated intra-function call warning for bl+mflr pattern

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250219162014.10334-1-sv@linux.ibm.com>
Date: Wed, 19 Feb 2025 21:50:14 +0530
From: Sathvika Vasireddy <sv@...ux.ibm.com>
To: jpoimboe@...nel.org, peterz@...radead.org, christophe.leroy@...roup.eu,
        npiggin@...il.com, maddy@...ux.ibm.com
Cc: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        llvm@...ts.linux.dev, sv@...ux.ibm.com
Subject: [RFC PATCH] objtool: Skip unannotated intra-function call warning for bl+mflr pattern

Architectures like PowerPC use a pattern where the compiler generates a
branch-and-link (bl) instruction that targets the very next instruction,
followed by loading the link register (mflr) later. This pattern appears
in the code like:

 bl .+4
 li r5,0
 mflr r30

Objtool currently warns about this as an "unannotated intra-function
call" because find_call_destination() fails to find any symbol at the
target offset. Add a check to skip the warning when a branch targets
the immediate next instruction in the same function.

Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202502180818.XnFdv8I8-lkp@intel.com/
Signed-off-by: Sathvika Vasireddy <sv@...ux.ibm.com>
---
 tools/objtool/check.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 753dbc4f8198..3f7cf2c917b5 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1613,6 +1613,7 @@ static struct symbol *find_call_destination(struct section *sec, unsigned long o
  */
 static int add_call_destinations(struct objtool_file *file)
 {
+	struct instruction *next_insn;
 	struct instruction *insn;
 	unsigned long dest_off;
 	struct symbol *dest;
@@ -1625,6 +1626,11 @@ static int add_call_destinations(struct objtool_file *file)
 		reloc = insn_reloc(file, insn);
 		if (!reloc) {
 			dest_off = arch_jump_destination(insn);
+
+			next_insn = next_insn_same_func(file, insn);
+			if (next_insn && dest_off == next_insn->offset)
+				continue;
+
 			dest = find_call_destination(insn->sec, dest_off);
 
 			add_call_dest(file, insn, dest, false);
-- 
2.39.3