Messages in this thread | | | Date | Wed, 13 Jul 2022 09:13:29 -0700 | From | Nathan Chancellor <> | Subject | Re: objtool "'naked' return found in RETHUNK build" with clang + CONFIG_K{A,C}SAN=y |
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On Wed, Jul 13, 2022 at 09:01:58AM -0700, Nick Desaulniers wrote: > On Wed, Jul 13, 2022 at 8:48 AM Nathan Chancellor <nathan@kernel.org> wrote: > > > > 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 > > Thanks for the report. I wonder if this might be a compiler bug; it > seems like the {a|t}san.module_{c|d}tor functions are being emitted > with ret instructions? > > If you have one of these builds lying around still, can you provide: > > $ llvm-objdump -dr --disassemble-symbols=tsan.module_ctor > arch/x86/kernel/fpu/bugs.o
Sure thing.
With KASAN:
$ llvm-objdump -r --disassemble-symbols=asan.module_ctor,asan.module_dtor build/arch/x86/kernel/fpu/bugs.o
build/arch/x86/kernel/fpu/bugs.o: file format elf64-x86-64
Disassembly of section .text.asan.module_ctor:
0000000000000000 <asan.module_ctor>: 0: be 01 00 00 00 movl $1, %esi 5: 48 c7 c7 00 00 00 00 movq $0, %rdi 0000000000000008: R_X86_64_32S .data c: e8 00 00 00 00 callq 0x11 <asan.module_ctor+0x11> 000000000000000d: R_X86_64_PLT32 __asan_register_globals-0x4 11: c3 retq
Disassembly of section .text.asan.module_dtor:
0000000000000000 <asan.module_dtor>: 0: be 01 00 00 00 movl $1, %esi 5: 48 c7 c7 00 00 00 00 movq $0, %rdi 0000000000000008: R_X86_64_32S .data c: e8 00 00 00 00 callq 0x11 <asan.module_dtor+0x11> 000000000000000d: R_X86_64_PLT32 __asan_unregister_globals-0x4 11: c3 retq
With KCSAN:
$ llvm-objdump -r --disassemble-symbols=tsan.module_ctor build/arch/x86/kernel/fpu/bugs.o
build/arch/x86/kernel/fpu/bugs.o: file format elf64-x86-64
Disassembly of section .text.tsan.module_ctor:
0000000000000000 <tsan.module_ctor>: 0: e8 00 00 00 00 callq 0x5 <tsan.module_ctor+0x5> 0000000000000001: R_X86_64_PLT32 __tsan_init-0x4 5: c3 retq
Cheers, Nathan
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