objtool: Silence more KCOV warnings

[ Upstream commit 6b023c7842048c4bbeede802f3cf36b96c7a8b25 ]

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@kernel.org>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/66a61a0b65d74e072d3dc02384e395edb2adc3c5.1742852846.git.jpoimboe@kernel.org
Closes: https://lore.kernel.org/Z9iTsI09AEBlxlHC@gmail.com
Closes: https://lore.kernel.org/oe-kbuild-all/202503180044.oH9gyPeg-lkp@intel.com/
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8ba5bcfd5cd572f3eca62ee2a1252dae15c57ee6..ddf3da6eccd0ddf69a7080662a428a4d3c51433c 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3569,6 +3569,9 @@ 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;
@@ -3788,6 +3791,9 @@ 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;
                }