objtool "'naked' return found in RETHUNK build" with clang + CONFIG_K{A,C}SAN=y

[Nathan Chancellor]

Hi Josh and Peter,

After commit 9bb2ec608a20 ("objtool: Update Retpoline validation") and
commit f43b9876e857 ("x86/retbleed: Add fine grained Kconfig knobs"), I
see a spew of objtool warnings when building certain configurations with
clang. Examples below, they appear to trigger in every single file.

With x86_64_defconfig + CONFIG_KASAN=y:

arch/x86/ia32/audit.o: warning: objtool: asan.module_ctor+0x11: 'naked' return found in RETHUNK build
arch/x86/ia32/audit.o: warning: objtool: asan.module_dtor+0x11: 'naked' return found in RETHUNK build
init/version.o: warning: objtool: asan.module_ctor+0x11: 'naked' return found in RETHUNK build
init/version.o: warning: objtool: asan.module_dtor+0x11: 'naked' return found in RETHUNK build
arch/x86/kernel/cpu/rdrand.o: warning: objtool: asan.module_ctor+0x11: 'naked' return found in RETHUNK build
arch/x86/kernel/cpu/rdrand.o: warning: objtool: asan.module_dtor+0x11: 'naked' return found in RETHUNK build
arch/x86/kernel/fpu/bugs.o: warning: objtool: asan.module_ctor+0x11: 'naked' return found in RETHUNK build
arch/x86/kernel/fpu/bugs.o: warning: objtool: asan.module_dtor+0x11: 'naked' return found in RETHUNK build
arch/x86/kernel/platform-quirks.o: warning: objtool: asan.module_ctor+0x0: 'naked' return found in RETHUNK build
init/calibrate.o: warning: objtool: asan.module_ctor+0x11: 'naked' return found in RETHUNK build
init/calibrate.o: warning: objtool: asan.module_dtor+0x11: 'naked' return found in RETHUNK build

With x86_64_defconfig + CONFIG_KCSAN=y:

arch/x86/ia32/audit.o: warning: objtool: tsan.module_ctor+0x5: 'naked' return found in RETHUNK build
init/calibrate.o: warning: objtool: tsan.module_ctor+0x5: 'naked' return found in RETHUNK build
init/version.o: warning: objtool: tsan.module_ctor+0x5: 'naked' return found in RETHUNK build
arch/x86/kernel/fpu/bugs.o: warning: objtool: tsan.module_ctor+0x5: 'naked' return found in RETHUNK build
arch/x86/kernel/cpu/rdrand.o: warning: objtool: tsan.module_ctor+0x5: 'naked' return found in RETHUNK build
arch/x86/events/probe.o: warning: objtool: tsan.module_ctor+0x5: 'naked' return found in RETHUNK build
arch/x86/kernel/apic/ipi.o: warning: objtool: tsan.module_ctor+0x5: 'naked' return found in RETHUNK build

If there is any additional information I can provide or patches I can
test, I am happy to do so!

Cheers,
Nathan