On Aug 17, 2012, at 10:16 PM, James Dennett wrote: > On Fri, Aug 17, 2012 at 4:00 PM, Nico Weber <[email protected]> wrote: >> On Fri, Aug 17, 2012 at 3:54 PM, Jordan Rose <[email protected]> wrote: >>> >>> On Aug 17, 2012, at 15:43 , David Blaikie <[email protected]> wrote: >>> >>>> On Fri, Aug 17, 2012 at 3:33 PM, Nico Weber <[email protected]> wrote: >>>>> Should this really be on by default? On chrome, this triggers a single >>>>> time (linux-only): >>>>> >>>>> ../../third_party/tcmalloc/chromium/src/stack_trace_table.cc:138:16: >>>>> warning: expression which evaluates to zero treated as a null pointer >>>>> constant of type 'void *' [-Wnon-literal-null-conversion] >>>>> out[idx++] = static_cast<uintptr_t>(0); >>>>> ^~~~~~~~~~~~~~~~~~~~~~~~~ >>>>> >>>>> out is declared as `void** out = new void*[out_len];`. The warning >>>>> isn't wrong, but it looks rather pedantic to me. Should this be only >>>>> in -Wall (or maybe even in -pedantic)? >>>> >>>> Might be a fair candidate for -Wall, though it did find some >>>> reasonable stuff in google. 18 cases overall with some fairly >>>> interesting ones (see b/6954211 for the ones that've been committed so >>>> far, or cl/32692314 for some of the remaining ones. >>>> >>>> The worst offenders are integer constants with value 0 that aren't at >>>> all intended to be pointers. (most easily occurred in function calls >>>> where the caller thought the argument was of one type but it's >>>> actually of a pointer type) >>>> >>>> I have some more once this warning opens up to cover comparisons, >>>> conditional operands, and return statements - there's a lot of >>>> confusing "cstr == '\0'" code where the user probably meant to deref >>>> the lhs but didn't. >>> >>> IMHO, this should remain on by default. The Chromium example clearly shows >>> an impedance mismatch between the array and the value being stored. I would >>> say it's not unlikely that at one point the array was a uintptr_t*, but was >>> changed, and this part of the code wasn't updated to match because it >>> didn't warn. But I can see the argument that "because this isn't harmful, >>> we shouldn't warn unless asked to". >> >> I don't feel strongly either way. This code is in one of the >> third-party libraries we use. We build those without -Wall because the >> warning policy is up to the library (not everybody believes in >> -Wall-clean), but we do build with the default warnings enabled so >> that clang can point out obvious bugs. It's easy for me to just >> disable this warning for the third-party library where it fires, but >> the warning felt like it's mostly pedantry. It sounds like it caught >> real bugs in google's internal code though, so *shrug* :-) > > FWIW, this seems a perfectly reasonable "on by default" warning to me, > and I'm struggling to see the pedantry. > > I think many users would be surprised that > static_cast<uintptr_t>(0) > is a null pointer constant, and I doubt that its author meant it that > way. I could be wrong.
I agree; this should be on-by-default as long as we're properly suppressing it in cases where the expression is a reasonable idiom for creating a pointer-sized null constant. (Ensuring that a null constant is pointer-sized is important when passing it to a variadic function). John. _______________________________________________ cfe-commits mailing list [email protected] http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
