linux-kernel - [PATCH 07/22] objtool: Silence more KCOV warnings

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Message-ID: <66a61a0b65d74e072d3dc02384e395edb2adc3c5.1742852846.git.jpoimboe@kernel.org>
Date: Mon, 24 Mar 2025 14:55:57 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Miroslav Benes <mbenes@...e.cz>,
	Brendan Jackman <jackmanb@...gle.com>,
	Nathan Chancellor <nathan@...nel.org>,
	kernel test robot <lkp@...el.com>
Subject: [PATCH 07/22] objtool: Silence more KCOV warnings

In the past there were issues with KCOV triggering unreachable
instruction warnings, which is why unreachable warnings are now disabled
with CONFIG_KCOV.

Now some new KCOV warnings are showing up with GCC 14:

  vmlinux.o: warning: objtool: cpuset_write_resmask() falls through to next function cpuset_update_active_cpus.cold()
  drivers/usb/core/driver.o: error: objtool: usb_deregister() falls through to next function usb_match_device()
  sound/soc/codecs/snd-soc-wcd934x.o: warning: objtool: .text.wcd934x_slim_irq_handler: unexpected end of section

All are caused by GCC KCOV not finishing an optimization, leaving behind
a never-taken conditional branch to a basic block which falls through to
the next function (or end of section).

At a high level this is similar to the unreachable warnings mentioned
above, in that KCOV isn't fully removing dead code.  Treat it the same
way by adding these to the list of warnings to ignore with CONFIG_KCOV.

Reported-by: Ingo Molnar <mingo@...nel.org>
Closes: https://lore.kernel.org/Z9iTsI09AEBlxlHC@gmail.com
Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202503180044.oH9gyPeg-lkp@intel.com/
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 tools/objtool/check.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8edb7044f7fc..032b3be409f2 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3493,6 +3493,9 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 			    !strncmp(func->name, "__pfx_", 6))
 				return 0;
 
+			if (file->ignore_unreachables)
+				return 0;
+
 			WARN("%s() falls through to next function %s()",
 			     func->name, insn_func(insn)->name);
 			return 1;
@@ -3702,6 +3705,9 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 		if (!next_insn) {
 			if (state.cfi.cfa.base == CFI_UNDEFINED)
 				return 0;
+			if (file->ignore_unreachables)
+				return 0;
+
 			WARN("%s: unexpected end of section", sec->name);
 			return 1;
 		}
-- 
2.48.1