Re: [PATCH v1 1/3] objtool/LoongArch: Fix fall through warning about efi_boot_kernel()

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Sep 01, 2025 at 03:21:54PM +0800, Tiezhu Yang 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()
> 
> This is because efi_boot_kernel() doesn't end with a return instruction
> or an unconditional jump, then objtool has determined that the function
> can fall through into the next function.
> 
> At the beginning, try to do something to make efi_boot_kernel() ends with
> an unconditional jump instruction, but it is not a proper way.
> 
> After more analysis, one simple way is to ignore these EFISTUB functions
> in validate_branch() of objtool since they are useless for stack unwinder.
> 

This is drivers/firmware/efi/libstub/loongarch.c:efi_boot_kernel(),
right?

Why not simply do something like:

diff --git a/drivers/firmware/efi/libstub/loongarch.c b/drivers/firmware/efi/libstub/loongarch.c
index 3782d0a187d1..082611a5f1f0 100644
--- a/drivers/firmware/efi/libstub/loongarch.c
+++ b/drivers/firmware/efi/libstub/loongarch.c
@@ -81,4 +81,5 @@ efi_status_t efi_boot_kernel(void *handle, efi_loaded_image_t *image,
 
 	real_kernel_entry(true, (unsigned long)cmdline_ptr,
 			  (unsigned long)efi_system_table);
+	BUG();
 }