On Mon, Dec 7, 2020 at 1:52 PM Marco Elver <elver@xxxxxxxxxx> wrote: > > On Mon, 7 Dec 2020 at 13:38, 'Dmitry Vyukov' via kasan-dev > <kasan-dev@xxxxxxxxxxxxxxxx> wrote: > > 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. > > It might be some check-for-builtins check gone wrong if it enables any > one of the sanitizers. That would be confirmed if it works with > > UBSAN_SANITIZE_kcov.o := n Yes, it "fixes" the warning. Initially I thought it's not a good solution because we want to detect UBSAN bugs in KCOV. But on second thought, if UBSAN detects a bug in KCOV, it may lead to infinite recursion. We already disable all other sanitizers on KCOV for this reason, so it's reasonable to disable UBSAN as well. And as a side effect it "resolves" the warning as well. I mailed: https://lore.kernel.org/lkml/20201209100152.2492072-1-dvyukov@xxxxxxxxxx/T/#u Thanks > > 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.
