linux-kernel - Re: [RFC PATCH 1/2] objtool/LoongArch: Fix fall through warning about efi_boot

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Message-ID: <CAAhV-H7m-BSqajDiDNMNEq4FY9uoCd9LZySOe0VQ+2Sv1wZZVg@mail.gmail.com>
Date: Tue, 26 Aug 2025 21:03:34 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Nathan Chancellor <nathan@...nel.org>, loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] objtool/LoongArch: Fix fall through warning about efi_boot_kernel()

On Tue, Aug 26, 2025 at 8:33 PM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
>
> On 2025/8/26 下午4:32, Huacai Chen wrote:
> > On Tue, Aug 26, 2025 at 2:46 PM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
> >>
> >> When compiling with LLVM and CONFIG_LTO_CLANG is set, there exists
> >> the following objtool warning:
> >>
> >>    vmlinux.o: warning: objtool: __efistub_efi_boot_kernel()
> >>    falls through to next function __efistub_exit_boot_func()
>
> ...
>
> >> -typedef void __noreturn (*kernel_entry_t)(bool efi, unsigned long cmdline,
> >> +typedef void (*kernel_entry_t)(bool efi, unsigned long cmdline,
> >>                                            unsigned long systab);
> >  From my point of view this is incorrect, this function is indeed a
> > noreturn function, and this modification makes LoongArch different to
> > other architectures.
> >
> > Maybe it is better to let objtool ignore the whole
> > drivers/firmware/efi/libstub directory. Because efistub is discarded
> > at runtime so it is useless for stack unwinder.
>
> I tested the following change but there is no effect, the objtool
> warning still exists, this is because OBJECT_FILES_NON_STANDARD
> does not work for link time validation of vmlinux.o according to
> tools/objtool/Documentation/objtool.txt.
Then I think objtool needs to be improved to handle this case, this
problem is not arch specific.

Huacai

>
> diff --git a/drivers/firmware/efi/Makefile b/drivers/firmware/efi/Makefile
> index 8efbcf699e4f..f1fff48eea76 100644
> --- a/drivers/firmware/efi/Makefile
> +++ b/drivers/firmware/efi/Makefile
> @@ -10,6 +10,8 @@
>   #
>   KASAN_SANITIZE_runtime-wrappers.o      := n
>
> +OBJECT_FILES_NON_STANDARD              := y
> +
>   obj-$(CONFIG_ACPI_BGRT)                += efi-bgrt.o
>   obj-$(CONFIG_EFI)                      += efi.o vars.o reboot.o
> memattr.o tpm.o
>   obj-$(CONFIG_EFI)                      += memmap.o
>
> Thanks,
> Tiezhu
>
>