On Mon, Dec 7, 2020 at 1:08 PM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > > > Hi all, > > > > > > After merging the akpm tree, today's linux-next build (powerpc > > > allyesconfig) produced warnings like this: > > > > > > kernel/kcov.c:296:14: warning: conflicting types for built-in function '__sanitizer_cov_trace_switch'; expected 'void(long unsigned int, void *)' [-Wbuiltin-declaration-mismatch] > > > 296 | void notrace __sanitizer_cov_trace_switch(u64 val, u64 *cases) > > > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > Odd. clang wants that signature, according to > > https://clang.llvm.org/docs/SanitizerCoverage.html. But gcc seems to > > want a different signature. Beats me - best I can do is to cc various > > likely culprits ;) > > > > Which gcc version? Did you recently update gcc? > > > > > ld: warning: orphan section `.data..Lubsan_data177' from `arch/powerpc/oprofile/op_model_pa6t.o' being placed in section `.data..Lubsan_data177' > > > > > > (lots of these latter ones) > > > > > > I don't know what produced these, but it is in the akpm-current or > > > akpm trees. > > I can reproduce this in x86_64 build as well but only if I enable > UBSAN as well. There were some recent UBSAN changes by Kees, so maybe > that's what affected the warning. > Though, the warning itself looks legit and unrelated to UBSAN. In > fact, if the compiler expects long and we accept u64, it may be broken > on 32-bit arches... No, I think it works, the argument should be uint64. I think both gcc and clang signatures are correct and both want uint64_t. The question is just how uint64_t is defined :) The old printf joke that one can't write portable format specifier for uint64_t. What I know so far: clang 11 does not produce this warning even with obviously wrong signatures (e.g. short). I wasn't able to trigger it with gcc on 32-bits at all. KCOV is not supported on i386 and on arm I got no warnings even with obviously wrong signatures (e.g. short). Using "(unsigned long val, void *cases)" fixes the warning on x86_64. I am still puzzled why gcc considers this as a builtin because we don't enable -fsanitizer-coverage on this file. I am also puzzled how UBSAN affects things. We could change the signature to long, but it feels wrong/dangerous because the variable should really be 64-bits (long is broken on 32-bits). Or we could introduce a typedef that is long on 64-bits and 'long long' on 32-bits.
