Messages in this thread | | | Date | Thu, 4 Jun 2020 17:25:37 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 1/2] kcov, objtool: Make runtime functions noinstr-compatible |
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On Thu, Jun 04, 2020 at 04:56:34PM +0200, Marco Elver wrote: > While we lack a compiler attribute to add to noinstr that would disable > KCOV, make the KCOV runtime functions return if the caller is in a > noinstr section. We then whitelist __sanitizer_cov_*() functions in > objtool.
> __sanitizer_cov_*() cannot safely become safe noinstr functions > as-is, as they may fault due to accesses to vmalloc's memory.
I would feel very much better with those actually in noinstr, because without it, there is nothing stopping us from adding a kprobe/hw- breakpoint or other funny to the function.
Even if they almost instra-return, having a kprobe on the function entry or condition check is enough to utterly wreck things.
So something like:
void noinstr __sanitizer_cov_trace_*(...) { if (within_noinstr_section(ip)) return;
instrumentation_begin(); write_comp_data(...); instrumentation_end(); }
Would make me feel a whole lot better.
> +static __always_inline bool in_noinstr_section(unsigned long ip) > +{ > + return (unsigned long)__noinstr_text_start <= ip && > + ip < (unsigned long)__noinstr_text_end; > +}
.entry.text is also considered noinstr, although I suppose that all being in .S files avoids it having annotations inserted, but perhaps a comment?
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