[PATCH 2/2] efi_loader: Fix kernel panic when FTRACE is enabled

[Patrick Rudolph]

On Fri, Dec 19, 2025 at 9:44 PM Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>
> On 12/17/25 11:39, Ilias Apalodimas wrote:
> > Thanks Patrick,
> >
> > On Wed, 17 Dec 2025 at 09:26, Patrick Rudolph
> > <patrick.rudolph at 9elements.com> wrote:
> >>
> >> When FTRACE is enabled the EFI runtime will call the tracing functions
> >> that are not marked as __efi_runtime and cause a kernel panic since
> >> the functions have been previously unmapped by the kernel.
> >>
> >> Resolve this issue by adding the 'notrace' attribute to '__efi_runtime'
> >> attribute and thus disable tracing the EFI runtime. If required this
> >> can be worked out latter.
>
> What is the point of actually booting with a U-Boot binary with FTRACE
> enabled? All your trace data will be lost.
>
> Wouldn't it be preferable to error out at ExitBootServices() and
> retrieve the trace?
>
> The current implementation of FTRACE looks flawed. The trace buffer
> should be allocated from LMB so that it cannot overwrite images or EFI data.
>
Hi Heinrich,
I'm not that familiar with the tracing yet. My expectation was that
the trace buffer is marked as reserved
and could be retrieved from /dev/mem, however that's not the case.
I updated the CONFIG_BOOTCOMMAND to write the trace file to disk
before it runs "bootflow scan"
as described in the documentation. I can then retrieve the trace data
from disk. That works for me.

Regards,
Patrick Rudolph

> Best regards
>
> Heinrich
>
> >>
> >
> > So I agree with this. Fixing is just a matter of moving the missing
> > functions to the runtime section, but I don;t think it's worth it,
> > unless someone *really* wants to instrument runtime calls.
> > OTOH runtime calls in the OS are rare and very limited
> >
> > Reviewed-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> >
> >
> >> TEST=Can boot a UEFI compatible linux OS on qemu-q35 when U-Boot was
> >>       built with FTRACE=1.
> >>
> >> Signed-off-by: Patrick Rudolph <patrick.rudolph at 9elements.com>
> >> ---
> >>   include/efi_loader.h | 2 +-
> >>   1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/include/efi_loader.h b/include/efi_loader.h
> >> index 3e70ac07055..7a13c390cbe 100644
> >> --- a/include/efi_loader.h
> >> +++ b/include/efi_loader.h
> >> @@ -66,7 +66,7 @@ struct bootflow;
> >>    *
> >>    *   static __efi_runtime compute_my_table(void);
> >>    */
> >> -#define __efi_runtime __section(".text.efi_runtime")
> >> +#define __efi_runtime __section(".text.efi_runtime") notrace
> >>
> >>   /*
> >>    * Call this with mmio_ptr as the _pointer_ to a pointer to an MMIO region
> >> --
> >> 2.52.0
> >>
>