Re: [lkp-robot] [include/linux/string.h] 6974f0c455: kernel_BUG_at_lib/string.c

[Daniel Micay <danielmicay@gmail.com>]

> So the fortify_string code has decided that only a single-byte (or
> empty) memcpy is ok.
> 
> And that, in turn, seems to be because we're copying from
> optprobe_template_entry, which is declared as
> 
>     extern __visible kprobe_opcode_t optprobe_template_entry;
> 
> so the fortify code decides it's a single character.
> 
> Does just changing all those things to be declared as arrays fix
> things?

Yeah, that fixes it because GCC will consider the size of 'char foo[]'
unknown (i.e. (size_t)-1 from __builtin_object_size).

GCC doesn't know this essentially constant value at compile-time so it
wasn't a compile-time error:

#define TMPL_END_IDX \
	((long)&optprobe_template_end - (long)&optprobe_template_entry)

-fsanitize=object-size works the same way for pointer dereferences so
replacing might fix some issues for CONFIG_UBSAN_SANITIZE_ALL. I guess
that's way too noisy at the moment thus the !COMPILE_TEST.