Eric Blake <ebl...@redhat.com> writes: > C99 requires SIZE_MAX to be declared with the same type as the > integral promotion of size_t, but OSX mistakenly defines it as > an 'unsigned long long' expression even though size_t is only > 'unsigned long'. Rather than futzing around with whether size_t > is 32- or 64-bits wide (which would be needed if we cared about > using SIZE_T in a #if expression), let the compiler get the right > type for us by virtue of integer promotion - if we later need it
By virtue of usual arithmetic conversions, actually. > during the preprocessor, the build will break on Mac until we > improve our replacement. > > See also https://patchwork.ozlabs.org/patch/542327/ for an > instance where the wrong type trips us up if we don't fix it > for good in osdep.h. > > Some versions of glibc make a similar mistake with SSIZE_MAX; the > goal is that the approach of this patch could be copied to work > around that problem if it ever becomes important to us. > > Signed-off-by: Eric Blake <ebl...@redhat.com> > > --- > v1 was here: > https://lists.gnu.org/archive/html/qemu-devel/2016-07/msg02520.html > > The topic recently came up again, and I noticed this patch sitting > on one of my older branches, so I've taken another shot at it. > https://lists.gnu.org/archive/html/qemu-devel/2016-10/msg00950.html > > v2: rewrite into a configure check (not sure if directly adding a > -D to QEMU_CFLAGS is the best, so advice welcome) > > v3: Use config-host.mak rather than direct -D > > v4: placate -Wunused builds > > I lack easy access to a Mac box, so this is untested as to whether > it actually solves the issue... > --- > include/qemu/osdep.h | 8 ++++++++ > configure | 16 ++++++++++++++++ > 2 files changed, 24 insertions(+) > > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h > index 9e9fa61..e06ac47 100644 > --- a/include/qemu/osdep.h > +++ b/include/qemu/osdep.h > @@ -141,6 +141,14 @@ extern int daemon(int, int); > # error Unknown pointer size > #endif > > +/* Mac OSX has a <stdint.h> bug that incorrectly defines SIZE_MAX with > + * the wrong type. Our replacement isn't usable in preprocessor > + * expressions, but it is sufficient for our needs. */ > +#if defined(HAVE_BROKEN_SIZE_MAX) && HAVE_BROKEN_SIZE_MAX > +#undef SIZE_MAX > +#define SIZE_MAX ((sizeof(char)) * -1) All right, let's see how this works. * -1 is of type int (C99 §6.4.4.1). * sizeof(char) is a clever way to say (size_t)1. * Integer promotion (§6.3.1.1) is a no-op for int, i.e. the left operand stays int. * Integer promotion is a no-op for size_t, since size_t is surely at least as wide as unsigned int. The right operand stays size_t. * The type of the multiplication is determined by the usual arithmetic conversions (§6.3.1.6). Since size_t's rank is surely greater or equal to int's rank, the int operand is converted to size_t, and the result is size_t. * The value of the expression is therefore (size_t)-1 * (size_t)1, yielding (size_t)-1. Cute, but what's wrong with straightforward #define SIZE_MAX ((size_t)-1) ? > +#endif > + > #ifndef MIN > #define MIN(a, b) (((a) < (b)) ? (a) : (b)) > #endif > diff --git a/configure b/configure > index 5751d8e..dd9e679 100755 > --- a/configure > +++ b/configure > @@ -1725,6 +1725,19 @@ if test "$cocoa" = "yes"; then > sdl=no > fi > > +# Some versions of Mac OS X incorrectly define SIZE_MAX > +cat > $TMPC << EOF > +#include <stdint.h> > +#include <stdio.h> > +int main(int argc, char *argv[]) { > + return printf("%zu", SIZE_MAX); > +} > +EOF > +have_broken_size_max=no > +if ! compile_object -Werror ; then > + have_broken_size_max=yes > +fi > + > ########################################## > # L2TPV3 probe > > @@ -5245,6 +5258,9 @@ fi > if test "$have_ifaddrs_h" = "yes" ; then > echo "HAVE_IFADDRS_H=y" >> $config_host_mak > fi > +if test "$have_broken_size_max" = "yes" ; then > + echo "HAVE_BROKEN_SIZE_MAX=y" >> $config_host_mak > +fi > > # Work around a system header bug with some kernel/XFS header > # versions where they both try to define 'struct fsxattr':