On Sun, Aug 19, 2012 at 2:35 PM, John McCall <[email protected]> wrote: > 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).
I believe NULL (which (well, GNUNull/__null does) seems to have the right target-dependent tweaks for size), nullptr, 0, and 0l, (0ul, 0u), etc should all work just fine. Did you have some other idiom(s) in mind for that particular purpose? - David _______________________________________________ cfe-commits mailing list [email protected] http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
