[Bug libc/16458] endian.h and netinet/in.h byte order macros return values of wrong type

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https://sourceware.org/bugzilla/show_bug.cgi?id=16458

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=6a1cefac196f45d766027c97a6c8c44459c9cccd

commit 6a1cefac196f45d766027c97a6c8c44459c9cccd
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Wed Jan 11 15:28:08 2017 +0000

    Make endian-conversion macros always return correct types (bug 16458).

    Bug 16458 reports that the endian-conversion macros in <endian.h> and
    <netinet/in.h>, in the case where no endian conversion is needed, just
    return their arguments without converting to the expected return type,
    so failing to act as expected for a macro version of a function.  (The
    <netinet/in.h> macros, in particular, are described with prototypes in
    POSIX so should act like correspondingly prototyped functions.)

    Where previously this was a fairly obscure issue, it now results in
    glibc build with GCC mainline breaking for big-endian systems:

    nss_hesiod/hesiod-service.c: In function '_nss_hesiod_getservbyport_r':
    nss_hesiod/hesiod-service.c:142:39: error: '%d' directive output may be
truncated writing between 1 and 11 bytes into a region of size 6
[-Werror=format-truncation=]
       snprintf (portstr, sizeof portstr, "%d", ntohs (port));
                                           ^~
    nss_hesiod/hesiod-service.c:142:38: note: using the range [1, -2147483648]
for directive argument
       snprintf (portstr, sizeof portstr, "%d", ntohs (port));
                                          ^~~~
    nss_hesiod/hesiod-service.c:142:3: note: format output between 2 and 12
bytes into a destination of size 6
       snprintf (portstr, sizeof portstr, "%d", ntohs (port));
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    The port argument is passed as int to this function, so when ntohs
    does not convert the compiler cannot tell that the result is within
    the range of uint16_t.  (I don't know if in fact it's possible for
    out-of-range values to reach this function and so get truncated as
    strings without this patch or as integers with it.)

    This patch arranges for these macros to use identity functions to
    ensure appropriate conversions while having warnings for implicit
    conversions of function arguments that might not occur with a cast.

    Tested for x86_64 and x86; with build-many-glibcs.py with GCC 6; and
    with build-many-glibcs.py with GCC mainline for powerpc to test the
    build fix.

        [BZ #16458]
        * bits/uintn-identity.h: New file.
        * inet/netinet/in.h: Include <bits/uintn-identity.h>.
        [__BYTE_ORDER == __BIG_ENDIAN] (ntohl): Use __uint32_identity.
        [__BYTE_ORDER == __BIG_ENDIAN] (ntohs): Use __uint16_identity.
        [__BYTE_ORDER == __BIG_ENDIAN] (htonl): Use __uint32_identity.
        [__BYTE_ORDER == __BIG_ENDIAN] (htohs): Use __uint16_identity.
        * string/endian.h: Include <bits/uintn-identity.h>.
        [__BYTE_ORDER == __LITTLE_ENDIAN] (htole16): Use
        __uint16_identity.
        [__BYTE_ORDER == __LITTLE_ENDIAN] (le16toh): Likewise.
        [__BYTE_ORDER == __LITTLE_ENDIAN] (htole32): Use
        __uint32_identity.
        [__BYTE_ORDER == __LITTLE_ENDIAN] (le32toh): Likewise.
        [__BYTE_ORDER == __LITTLE_ENDIAN] (htole64): Use
        __uint64_identity.
        [__BYTE_ORDER == __LITTLE_ENDIAN] (le64toh): Likewise.
        [__BYTE_ORDER != __LITTLE_ENDIAN] (htobe16): Use
        __uint16_identity.
        [__BYTE_ORDER != __LITTLE_ENDIAN] (be16toh): Likewise.
        [__BYTE_ORDER != __LITTLE_ENDIAN] (htobe32): Use
        __uint32_identity.
        [__BYTE_ORDER != __LITTLE_ENDIAN] (be32toh): Likewise.
        [__BYTE_ORDER != __LITTLE_ENDIAN] (htobe64): Use
        __uint64_identity.
        [__BYTE_ORDER != __LITTLE_ENDIAN] (be64toh): Likewise.
        * string/Makefile (headers): Add bits/uintn-identity.h.
        (tests): Add test-endian-types.
        * string/test-endian-types.c: New file.
        * inet/Makefile (tests): Add test-hnto-types.
        * inet/test-hnto-types.c: New file.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                  |   34 +++++++++++++++++++++++++++++
 bits/uintn-identity.h      |   50 ++++++++++++++++++++++++++++++++++++++++++++
 inet/Makefile              |    2 +-
 inet/netinet/in.h          |    9 ++++---
 inet/test-hnto-types.c     |   39 ++++++++++++++++++++++++++++++++++
 string/Makefile            |    5 ++-
 string/endian.h            |   25 +++++++++++----------
 string/test-endian-types.c |   49 +++++++++++++++++++++++++++++++++++++++++++
 8 files changed, 194 insertions(+), 19 deletions(-)
 create mode 100644 bits/uintn-identity.h
 create mode 100644 inet/test-hnto-types.c
 create mode 100644 string/test-endian-types.c

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