On 12/23/2014 03:22 PM, Peter Maydell wrote: > The mingw32 compiler complains about trying to print variables of type > ssize_t with the %z format string specifier. Since we're printing it > as unsigned hex anyway, cast to size_t to silence the warning.
Hmm. I wonder if mingw headers are mixing 'long' and 'unsigned int' (or maybe 'unsigned long' and 'int') for the underlying definitions of 'ssize_t' vs. 'size_t'; both are 32-bits on the platform, but a difference in underlying type would definitely explain why you get a compiler warning if you use %zd with size_t or %zu with ssize_t. On the other hand, the warning I've most often seen is that native windows completely lacks %z support, so gcc is smart enough to warn that ANY use of %z is not going to work, for a function marked __attribute__((__printf__)) on mingw. > > Signed-off-by: Peter Maydell <peter.mayd...@linaro.org> > --- > I suspect that this is a compiler bug, but this is the only instance > in the codebase so I'm prepared to work around it to get to a point > where we can turn on warnings-as-errors for w32, because some of the > w32-specific errors really are flagging up issues we need to fix. With new enough mingw headers, the alternative solution is to guarantee that #__USE_MINGW_ANSI_STDIO is defined before including standard headers, then %z, %j, %lld, and other required constructs magically work (because you are no longer using the native printf, but the fixed mingw shim). Once you do that, you want to use __attribute__((__gnu_printf__)) instead of __attribute__((__printf__)) in order to teach gcc that yes, your use of %z is really going to work. For some more background reading: http://sourceforge.net/p/mingw-w64/wiki2/gnu%20printf/ https://lists.gnu.org/archive/html/bug-gnulib/2014-12/msg00029.html > --- > hw/ppc/spapr.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c > index 08401e0..9aaa800 100644 > --- a/hw/ppc/spapr.c > +++ b/hw/ppc/spapr.c > @@ -1438,7 +1438,7 @@ static void ppc_spapr_init(MachineState *machine) > } > if (spapr->rtas_size > RTAS_MAX_SIZE) { > hw_error("RTAS too big ! 0x%zx bytes (max is 0x%x)\n", > - spapr->rtas_size, RTAS_MAX_SIZE); > + (size_t)spapr->rtas_size, RTAS_MAX_SIZE); What's the actual compiler warning you got? This feels like it won't work if the real problem is the compiler telling you that %z is unknown; conversely, if it is a mismatch between 'size_t' vs. 'ssize_t', we probably ought to report it to the mingw folks to fix their environment to use the same underlying type for signed vs. unsigned sizes. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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