On 2018-09-26 20:57, Peter Maydell wrote: > On 26 September 2018 at 16:59, Thomas Huth <th...@redhat.com> wrote: > >> +/* >> + * Clang 3.4 claims to be compatible with GCC 4.2, but does not have the >> + * "flatten" attribute, so we've got to handle Clang via __has_attribute >> here >> + */ >> +#if defined(__clang__) && defined(__has_attribute) >> +# if __has_attribute(flatten) >> +# define QEMU_FLATTEN __attribute__((flatten)) >> +# endif >> +#elif !defined(__clang__) && QEMU_GNUC_PREREQ(4, 1) >> +# define QEMU_FLATTEN __attribute__((flatten)) >> +#endif >> +#ifndef QEMU_FLATTEN >> +# define QEMU_FLATTEN >> +#endif > > I think it would be cleaner to say: if we have __has_attribute, > trust it; otherwise fall back to version testing. Also, we > already require at least GCC 4.1 so a version test against > that is unnecessary. So something like: > > #ifndef __has_attribute > #define __has_attribute(x) 0 / compatibility with older GCC */ > #endif > > /* > * gcc doesn't provide __has_attribute() until gcc 5, > * but we know all the gcc versions we support have flatten. > * clang may not have flatten but always has __has_attribute(). > */ > #if __has_attribute(flatten) || !defined(__clang__) > # define QEMU_FLATTEN __attribute__((flatten)) > #else > # define QEMU_FLATTEN > #endif
Good idea, I'll send a v2 with that. Speaking of the minimum GCC version that we require: Did we ever officially define that? Or is it just a result from appendix C in our qemu-doc? I guess the minimum GCC could be defined to 4.2 since that's the compiler that was still used in OpenBSD recently, before they switched to Clang? Maybe we should add a list in our qemu-doc with some minimum versions that we require (e.g. also glib), so that it is easier to look this up? Also when searching for GNUC_PREREQ in the sources, there are at least some occurances in tests/tcg/arm/fcvt.c and include/fpu/softfloat-macros.h which we could simplify these days... Thomas
