Hi all, I've found the places responsible for the warnings, but before I do anything I'd like to discuss a couple of things.
1. What would a good name for the warning switch be? How does -Wreturning-noreturn sound? 2. I've thought about this for a while, and I feel like throwing a warning for a noreturn method that isn't explicitly noreturn in the Control Flow Graph is a little too harsh. The point of the attribute is to hint to gcc that the method will never return even if it appears so, and requiring that the body explicitly do something like call abort() or loop infinitely kind of defeats the purpose of the attribute, in my opinion 3. If (2) is just me missing something, should I split the warning into 2 different warnings for a noreturn definition with an explicit return statement and an implicit one in the case of a method not explicitly throwing/looping infinitely, etc? Thoughts? best regards, Julian On Wed, Jul 5, 2023 at 9:13 PM Julian Waters <tanksherma...@gmail.com> wrote: > Hi Jonathan, > > Thanks for the reply, is there a place in gcc's source code I could look > at for this? As for the returning an explicit value from noreturn, I'm > unfortunately not the one who wrote the code that way; I'm merely a build > systems developer trying to get it to work with gcc :/ > > best regards, > Julian > > On Wed, 5 Jul 2023, 19:26 Jonathan Wakely, <jwakely....@gmail.com> wrote: > >> On Wed, 5 Jul 2023 at 12:01, Julian Waters via Gcc <gcc@gcc.gnu.org> >> wrote: >> > >> > I see, thanks Andrew. >> > >> > Anyone else have opinions on this besides Liu or Andrew? The responses >> have >> > been surprisingly quiet thus far >> >> IMHO all warnings should have an option controlling them, so that you >> can disable them via pragmas. >> >> But I agree that you shouldn't need to return from a noreturn >> function, it can either throw or use __builtin_unreachable() on the >> line where you currently return. >> >> >> > >> > best regards, >> > Julian >> > >> > On Wed, 5 Jul 2023, 09:40 Andrew Pinski, <pins...@gmail.com> wrote: >> > >> > > On Tue, Jul 4, 2023 at 6:32 PM Julian Waters <tanksherma...@gmail.com >> > >> > > wrote: >> > > > >> > > > Hi Andrew, thanks for the quick response, >> > > > >> > > > What if the method has a return value? I know it sounds >> > > counterintuitive, but in some places HotSpot relies on the noreturn >> > > attribute being applied to methods that do return a value in an >> unreachable >> > > code path. Does the unreachable builtin cover that case too? >> > > >> > > It is wrong to use noreturn on a function other than one which has a >> > > return type of void as documented. >> > > >> > > >> https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noreturn-function-attribute >> > > : >> > > ``` >> > > It does not make sense for a noreturn function to have a return type >> > > other than void. >> > > ``` >> > > >> > > Thanks, >> > > Andrew Pinski >> > > >> > > >> > > > >> > > > best regards. >> > > > Julian >> > > > >> > > > On Wed, Jul 5, 2023 at 9:07 AM Andrew Pinski <pins...@gmail.com> >> wrote: >> > > >> >> > > >> On Tue, Jul 4, 2023 at 5:54 PM Julian Waters via Gcc < >> gcc@gcc.gnu.org> >> > > wrote: >> > > >> > >> > > >> > Hi all, >> > > >> > >> > > >> > Currently to disable the warning that a noreturn method does >> return, >> > > it's >> > > >> > required to disable warnings entirely. This can be very >> inconvenient >> > > when >> > > >> > -Werror is enabled with a noreturn method that isn't specifically >> > > calling >> > > >> > something like std::abort() at the end, when one wants all other >> > > -Wall and >> > > >> > -Wextra warnings to be reported, for instance in the Java >> HotSpot VM >> > > (which >> > > >> > I'm currently adapting to compile with gcc on all supported >> > > platforms). Is >> > > >> > there a possibility we can add a disable warning option >> specifically >> > > for >> > > >> > this case? Something like -Wno-returning-noreturn. I'm >> interested in >> > > adding >> > > >> > this myself if it's not convenient for gcc's maintainers to do >> so at >> > > the >> > > >> > moment, but I'd need some guidance on where to look and what the >> > > relevant >> > > >> > code is >> > > >> >> > > >> You could just add >> > > >> __builtin_unreachable(); (or std::unreachable(); if you are C++23 >> or >> > > >> unreachable() if you are using C23). >> > > >> Or even add while(true) ; >> > > >> >> > > >> I am pretty sure not having an option is on purpose and not really >> > > >> interested in adding an option here because of the above >> workarounds. >> > > >> >> > > >> Thanks, >> > > >> Andrew Pinski >> > > >> >> > > >> > >> > > >> > best regards, >> > > >> > Julian >> > > >> >
