Re: [PATCH v10 18/30] tracing: Check for undefined symbols in simple_ring_buffer

[Steven Rostedt <rostedt@goodmis.org>]

On Mon, 26 Jan 2026 10:44:07 +0000
Vincent Donnefort <vdonnefort@google.com> wrote:

> The simple_ring_buffer implementation must remain simple enough to be
> used by the pKVM hypervisor. Prevent the object build if unresolved
> symbols are found.
> 
> Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

-- Steve

> 
> diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
> index 9e86c43bf320..9f675d5d27c7 100644
> --- a/kernel/trace/Makefile
> +++ b/kernel/trace/Makefile
> @@ -131,4 +131,20 @@ obj-$(CONFIG_TRACE_REMOTE) += trace_remote.o
>  obj-$(CONFIG_SIMPLE_RING_BUFFER) += simple_ring_buffer.o
>  obj-$(CONFIG_TRACE_REMOTE_TEST) += remote_test.o
>  
> +#
> +# simple_ring_buffer is used by the pKVM hypervisor which does not have access
> +# to all kernel symbols. Fail the build if forbidden symbols are found.
> +#
> +UNDEFINED_ALLOWLIST := memset alt_cb_patch_nops __x86 __ubsan __asan __kasan __gcov __aeabi_unwind
> +UNDEFINED_ALLOWLIST += __stack_chk_fail stackleak_track_stack __ref_stack __sanitizer
> +UNDEFINED_ALLOWLIST := $(addprefix -e , $(UNDEFINED_ALLOWLIST))
> +
> +quiet_cmd_check_undefined = NM      $<
> +      cmd_check_undefined = test -z "`$(NM) -u $< | grep -v $(UNDEFINED_ALLOWLIST)`"
> +
> +$(obj)/%.o.checked: $(obj)/%.o FORCE
> +	$(call if_changed,check_undefined)
> +
> +always-$(CONFIG_SIMPLE_RING_BUFFER) += simple_ring_buffer.o.checked
> +
>  libftrace-y := ftrace.o