Does __sanitizer_cov_trace_pc inserted for assembly code?

[Joey Jiao]

Hi,

Just to confirm if __sanitizer_cov_trace_pc instrument happend for pure assembly functions in .S file?

I checked several function like __arch_copy_from_user which seems not.

Also SanitizerCoverage.cpp in llvm code seems doesn't support it, right?

THX

Joey

[Dmitry Vyukov]

Hi Joey,

You are right. Instrumentation is not insured into asm files. It's
done by C compiler which does not compile asm.

But I also think it's not really necessary for __arch_copy_from_user.
It does not contain any interesting branches that depend on the user
inputs. There is one: failure/non-failure case, but it should affect
branching in the caller code, which is C and which is instrumented. So
the fuzzer will be able to observe that branch indirectly.