https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116854
--- Comment #13 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Anonymous from comment #8) > (In reply to Thiago Macieira from comment #5) > > > This has nothing to do with -march=native. In fact, for the Gentoo people > > who are using -march=native, everything is fine because __RDRND__ is *not* > > defined (I think; I don't have such a CPU to check, but on my TGL, > > -march=native and -march=tigerlake differ). > > I have to disagree. I specifically stated in the Qt bug that affected users > were using -march=native and that was being resolved to -march=bdver4, so What does "being resolved to -march=bdver4" mean? Could you please provide the output of the command shown in comment 1? gcc -march=native -### hello.c That will resolve to a specific -march option **and** zero or more -m options for specific instructions. If -march=native resolves to **only** -march=bdver4 on your machine (as you seem to be suggesting) then that's a problem. But if it resolves to -march=bdver4 -mno-rdrnd then GCC is behaving correctly. > everything is not fine when using -march=native. You are correct that with > -march=native on an affected CPU, __RDRND__ is not defined, Well then that suggests -march=native includes -mno-rdrnd and so GCC is behaving correctly. > but that's what > I used to build Qt libraries that segfaulted. I only got working libraries > by supplying -march=x86-64-v2 or omitting -march entirely. > > This is why I was asking in the Qt bug about the lack of definition for > __RDRND__ when GCC is supplied with -march=native, and whether the > explanation about __haswell__ still worked - because nobody involved is > supplying -march=bdver4 as a compiler argument, everyone is using > -march=native and trusting gcc to make a decision on the correct environment. Which contradicts what Thiago said above. We really need some clarity here to do anything. Please run the -### command to give some concrete facts about what GCC is actually doing on a machine with the relevant CPU. Then please also provide the output of: gcc -march=native -E -dM -x c /dev/null | grep -E -i '__tune_|rdrnd'
