linux-kernel - [PATCH v1 1/3] objtool/LoongArch: Fix fall through warning about efi_boot

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Message-ID: <20250901072156.31361-2-yangtiezhu@loongson.cn>
Date: Mon,  1 Sep 2025 15:21:54 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Nathan Chancellor <nathan@...nel.org>
Cc: loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH v1 1/3] objtool/LoongArch: Fix fall through warning about efi_boot_kernel()

When compiling with LLVM and CONFIG_LTO_CLANG is set, there exists
the following objtool warning:

  vmlinux.o: warning: objtool: __efistub_efi_boot_kernel()
  falls through to next function __efistub_exit_boot_func()

This is because efi_boot_kernel() doesn't end with a return instruction
or an unconditional jump, then objtool has determined that the function
can fall through into the next function.

At the beginning, try to do something to make efi_boot_kernel() ends with
an unconditional jump instruction, but it is not a proper way.

After more analysis, one simple way is to ignore these EFISTUB functions
in validate_branch() of objtool since they are useless for stack unwinder.

Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
---
 tools/objtool/check.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index d14f20ef1db1..2dcebf75d95e 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3567,6 +3567,10 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 			    !strncmp(func->name, "__pfx_", 6))
 				return 0;

+			/* Ignore EFISTUB functions which are useless for stack unwinder */
+			if (!strncmp(func->name, "__efistub_", 10))
+				return 0;
+
 			if (file->ignore_unreachables)
 				return 0;

-- 
2.42.0