[tip: objtool/urgent] objtool: Silence more KCOV warnings

[tip-bot2 for Josh Poimboeuf]

The following commit has been merged into the objtool/urgent branch of tip:

Commit-ID:     6b023c7842048c4bbeede802f3cf36b96c7a8b25
Gitweb:        https://git.kernel.org/tip/6b023c7842048c4bbeede802f3cf36b96c7a8b25
Author:        Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate:    Mon, 24 Mar 2025 14:55:57 -07:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 25 Mar 2025 09:20:26 +01:00

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@xxxxxxxxxx>
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/66a61a0b65d74e072d3dc02384e395edb2adc3c5.1742852846.git.jpoimboe@xxxxxxxxxx
Closes: https://lore.kernel.org/Z9iTsI09AEBlxlHC@xxxxxxxxx
Closes: https://lore.kernel.org/oe-kbuild-all/202503180044.oH9gyPeg-lkp@xxxxxxxxx/
---
 tools/objtool/check.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 2f7aff1..cb66e6b 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3485,6 +3485,9 @@ 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;
@@ -3694,6 +3697,9 @@ 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;
 		}