On Thu, Feb 02, 2017 at 03:31:03PM -0800, Shu Shen wrote:
> On Thu, Feb 02, 2017 at 03:08:09PM -0800, Ben Pfaff wrote:
> > On Thu, Feb 02, 2017 at 02:55:03PM -0800, Shu Shen wrote:
> > > On Tue, Jan 31, 2017 at 10:45:31AM -0800, Ben Pfaff wrote:
> > > > By my count, vlan_tci_to_pcp() is used in printf-like format
> > > > specifiers in 7 places in the tree. Before this patch, it is used
> > > > with the following format specifiers:
> > > >
> > > > %d 3 times %x 1 time PRIu8 1 time PRIx8 1 time
> > > >
> > > > Both %d and %x are obviously correct, portable format specifiers for
> > > > int, which is the return type of vlan_tci_to_pcp(). I contend that
> > > > PRIu8 and PRIx8 should be acceptable too because the integer
> > > > promotions convert uint8_t to int anyway.
> > > The problem is that PRIu8 and PRIx8 the specifiers are not promoted to
> > > 'u' and 'x' respectively on macOS.
> > >
> > > For example, for PRIu*, on Mac OS, /usr/include/inttypes.h:
> > >
> > > # define __PRI_8_LENGTH_MODIFIER__ "hh"
> > > # define __PRI_64_LENGTH_MODIFIER__ "ll"
> > > # define PRIu8 __PRI_8_LENGTH_MODIFIER__ "u"
> > > # define PRIu16 "hu"
> > > # define PRIu32 "lu"
> > > # define PRIu64 __PRI_64_LENGTH_MODIFIER__ "u"
> > >
> > > While on Linux/glibc, /usr/include/inttypes.h:
> > >
> > > # define PRIu8 "u"
> > > # define PRIu16 "u"
> > > # define PRIu32 "u"
> > > # define PRIu64 __PRI64_PREFIX "u"
> > >
> > > where all PRIu* except PRIu64 are the same.
> > >
> > > Therefore, using PRIu8 or PRIx8 with the int return type of
> > > vlan_tci_to_pcp() is causing compiler warnings on macOS.
> >
> > What are the warnings?
> See https://travis-ci.org/openvswitch/ovs/jobs/197378752#L1303
> There are plenty of other warnings due to similar situation (if they are
> not problems).
>
> >
> > There is no real problem with using %hhd or %hhu to print an int,
> > because printf() cannot tell the difference between an int and a char:
> > they are both passed as int.
> You may be right about printf with regard to an int and a char. But how
> about an int specifier and a long variable?
>
> When I noticed the Wformat warning messages on macOS, I have no idea
> whether there is a hidden issue where the format specifier might be
> truncating a variable.
>
> The only way to be sure is to clean up the code base to remove the
> warning messages even if they are just noise.
I sent a patch that does this the way that makes more sense to me:
https://patchwork.ozlabs.org/patch/736405/
Thank you for raising the issue.
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