On 20/02/2023 12:59, Xi Ruoyao wrote: > On Mon, 2023-02-20 at 11:30 +0000, Jonny Grant wrote: > >> Thank you for the suggestion, I gave that nonnull attribute a try, but >> it doesn't appear to warn for this example. >> >> https://godbolt.org/z/boqTj6oWE > > Ouch... The optimizer inlined make_std_string so both -Wnonnull and - > fanalyzer fails to catch the issue here. > > Adding noipa attribute for make_std_string will work, but will also > cause the generated code stupidly slow. Maybe: > > #ifdef WANT_DIAGNOSTIC > #define MAKE_STD_STRING_ATTR __attribute__ ((noipa, nonnull)) > #else > #define MAKE_STD_STRING_ATTR > #endif > > std::string make_std_string(const char * const str) MAKE_STD_STRING_ATTR; > > It still looks very stupid though. Hi, thank you for your reply and investigation. I raised this issue here that you spotted https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108871 > >> Feels useful to get build warnings if compiler knows nullptr is going >> to be dereferenced, as clang does. > > The problem is in this case nullptr is not dereferenced, at all. So if > we want a warning here we'll have to invent some new __builtin or > __attribute__ to give the compiler a hint. AFAIK there is no such > facility now. > > And you cannot simply justifying to add a new facility because "I feel > it useful". Generally you need to show the benefit will be at least > equally great than the maintenance burden introduced into the GCC code > base. And unfortunately usually we can only measure the burden after > really writing all the code... So it's not easy to convince someone to > develop such a new feature. > >> Personally I feel runtime should equally handle possible nullptr by >> constructing strings in a try catch block so any exceptions are >> handled or logged at least... > > A portable runtime should not assume std::string(NULL) will raise an > exception because other C++ standard libraries may behave differently. > The portable solution is to make a wrapper around std::string > constructor and check if the parameter is NULL. > >> Personally I would be pleased if GCC had a warning I could enable to >> report any logic_error exceptions it knew would execute. > > Or maybe when a program will definitely raise an uncatched exception. > But is the feature really useful? This will not happen for anything > other than simple toy programs. >
