Re: [PATCH v2 11/13] x86/entry/fred: encode frame pointer on entry

[David Stevens]

Setting aside the rest of the RFC, should this patch be merged? If
someone tries to use CONFIG_UNWINDER_FRAME_POINTER on a system with
FRED, they'll get a "kernel stack regs ... has bad 'bp' value" warning
in the logs the first time the unwinder runs.

Thanks,
David

On Fri, Apr 24, 2026 at 12:17 PM David Stevens <stevensd@xxxxxxxxxx> wrote:
>
> Add missing ENCODE_FRAME_POINTER macro invocation into FRED_ENTER macro,
> to prevent the unwinder from encountering a NULL stack frame pointer
> when CONFIG_UNWINDER_FRAME_POINTER is enabled
>
> Fixes: 14619d912b65 ("x86/fred: FRED entry/exit and dispatch code")
> Signed-off-by: David Stevens <stevensd@xxxxxxxxxx>
> ---
>  arch/x86/entry/entry_64_fred.S | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/x86/entry/entry_64_fred.S b/arch/x86/entry/entry_64_fred.S
> index 894f7f16eb80..119b8214748e 100644
> --- a/arch/x86/entry/entry_64_fred.S
> +++ b/arch/x86/entry/entry_64_fred.S
> @@ -7,6 +7,7 @@
>  #include <linux/kvm_types.h>
>
>  #include <asm/asm.h>
> +#include <asm/frame.h>
>  #include <asm/fred.h>
>  #include <asm/segment.h>
>
> @@ -19,6 +20,7 @@
>         UNWIND_HINT_END_OF_STACK
>         ANNOTATE_NOENDBR
>         PUSH_AND_CLEAR_REGS
> +       ENCODE_FRAME_POINTER
>         movq    %rsp, %rdi      /* %rdi -> pt_regs */
>  .endm
>
> --
> 2.54.0.rc2.544.gc7ae2d5bb8-goog
>