On Tue, 25 Jan 2022 22:27:32 +0900 Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote: > > /* > > * struct trace_event_data_offsets_<call> { > > * u32 <item1>; > > * u32 <item2>; > > * [...] > > * }; > > * > > * The __dynamic_array() macro will create each u32 <item>, this is > > * to keep the offset of each array from the beginning of the event. > > * The size of an array is also encoded, in the higher 16 bits of > > * <item>. > > */ > > > > So, I think -Warray-bounds is refusing to see the destination as > > anything except a u32, but being accessed at 4 (sizeof(u32)) + 8 > > (address && 0xffff) (?) > > Ah, I got it. Yes, that's right. __data_loc() will access the data > from the __entry, but the __rel_loc() points the same address from > the encoded field ("__rel_loc_foo" in this case) itself. > This is introduced for the user application event, which doesn't > know the actual __entry size because the __entry includes some > kernel internal defined fields. > > > But if this is true, I would imagine there would be plenty of other > > warnings? I'm currently stumped. > > That is because __rel_loc is used only in the sample code in the kernel > for testing. Other use-cases comes from user-space. > Hmm, can we skip this boundary check for this example? If the -Warray-bounds determines the destination array size from the type of given pointer, we can just change the macro as below; #define __get_rel_dynamic_array(field) ((void *)__entry + \ offsetof(typeof(*__entry), __rel_loc_##field) + \ sizeof(__entry->__rel_loc_##field) + \ (__entry->__rel_loc_##field & 0xffff)) This must works same as __get_dynamic_array() macro. Could you try this patch? >From 2982ba01367ec1f746a4f128512436e5325a7f9d Mon Sep 17 00:00:00 2001 From: Masami Hiramatsu <mhiramat@xxxxxxxxxx> Date: Tue, 25 Jan 2022 23:19:30 +0900 Subject: [PATCH] tracing: Avoid -Warray-bounds warning for __rel_loc macro Since -Warray-bounds checks the destination size from the type of given pointer, __assign_rel_str() macro gets warned because it passes the pointer to the 'u32' field instead of 'trace_event_raw_*' data structure. Pass the data address calculated from the 'trace_event_raw_*' instead of 'u32' __rel_loc field. Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx> Reported-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> --- include/trace/trace_events.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/include/trace/trace_events.h b/include/trace/trace_events.h index 8c6f7c433518..65d927e059d3 100644 --- a/include/trace/trace_events.h +++ b/include/trace/trace_events.h @@ -318,9 +318,10 @@ TRACE_MAKE_SYSTEM_STR(); #define __get_str(field) ((char *)__get_dynamic_array(field)) #undef __get_rel_dynamic_array -#define __get_rel_dynamic_array(field) \ - ((void *)(&__entry->__rel_loc_##field) + \ - sizeof(__entry->__rel_loc_##field) + \ +#define __get_rel_dynamic_array(field) \ + ((void *)__entry + \ + offsetof(typeof(*__entry), __rel_loc_##field) + \ + sizeof(__entry->__rel_loc_##field) + \ (__entry->__rel_loc_##field & 0xffff)) #undef __get_rel_dynamic_array_len -- 2.25.1 -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>