On Fri, Jan 29, 2021 at 11:38 AM Joel Sherrill <joel.sherr...@gmail.com> wrote:
> > > On Fri, Jan 29, 2021, 12:28 PM Sebastian Huber < > sebastian.hu...@embedded-brains.de> wrote: > >> On 29/01/2021 18:33, Peter Dufault wrote: >> >> >>> Do not use an enum as a bit field. Document the state flags. >> >>> >> >>> >> >>> Is this a new style rule that needs to be documented? >> >> Into which category would you put this? Language and Compiler? >> >> >> >> https://docs.rtems.org/branches/master/eng/coding-conventions.html >> >> >> >> >> >> Yes. >> >> >> >> >> > I use enums as bit fields a lot. I use them in conjunction with objects >> that are the same enum. >> > >> > I avoid using #define. In most situations you can't print them in a >> debugger and they imply restricted usage. >> > >> > Is this an appropriate warning? Does it always mean that the enum >> should be replaced with a #define? >> > >> > If it doesn't always apply then the style should make it clear when it >> should apply. >> >> We don't have to agree with Coverity. This is why I asked before the >> change: >> >> https://lists.rtems.org/pipermail/devel/2021-January/064105.html >> >> From my point of view enums are useful for bit fields and I don't think >> this point of view is too exotic since debuggers such as GDB and >> Lauterbach support it. For example: >> >> enum a { >> A, >> B, >> C >> }; >> >> enum a f(enum a x, enum a y) >> { >> return x | y; >> } >> >> enum a v; >> >> int main() >> { >> v = f(B, C); >> return 0; >> } >> >> Breakpoint 1, main () at test.c:16 >> 16 v = f(B, C); >> (gdb) n >> 17 return 0; >> (gdb) p v >> $1 = (B | C) >> > > If we want enums as bitfields, we can add that as a coding guideline as an > option and mention that some static analysis tools do not like it. > > Then mark these all as ignored with an explanation > My only concern is whether the behavior is always well-defined (by the C standards). I'm not an expert and don't know where to find an answer to that question. What I seem to glean from a quick search is that the main requirement is that the type is guaranteed consistent with char, signed int, or unsigned int. So bit manipulations would seem to be well-defined. Does coverity offer any guidance why it complains? > >> -- >> embedded brains GmbH >> Herr Sebastian HUBER >> Dornierstr. 4 >> 82178 Puchheim >> Germany >> email: sebastian.hu...@embedded-brains.de >> phone: +49-89-18 94 741 - 16 >> fax: +49-89-18 94 741 - 08 >> >> Registergericht: Amtsgericht München >> Registernummer: HRB 157899 >> Vertretungsberechtigte Geschäftsführer: Peter Rasmussen, Thomas Dörfler >> Unsere Datenschutzerklärung finden Sie hier: >> https://embedded-brains.de/datenschutzerklaerung/ >> >> _______________________________________________ >> devel mailing list >> devel@rtems.org >> http://lists.rtems.org/mailman/listinfo/devel >> >
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