[U-Boot] [PATCH 1/1] net: remove superfluous __packed attribute

[Tom Rini]

On Mon, Nov 04, 2019 at 07:07:46PM +0100, Heinrich Schuchardt wrote:
> On 10/12/19 3:29 PM, Heinrich Schuchardt wrote:
> > On 10/3/19 8:01 PM, Heinrich Schuchardt wrote:
> > > On 10/3/19 7:09 PM, Tom Rini wrote:
> > > > On Thu, Oct 03, 2019 at 07:01:22PM +0200, Heinrich Schuchardt wrote:
> > > > 
> > > > > struct ip_udp_hdr is naturally packed. There is no point in adding a
> > > > > __packed attribute. With the attribute the network stack does not
> > > > > compile
> > > > > using GCC 9.2.1:
> > > > > 
> > > > > net/net.c: In function ‘net_process_received_packet’:
> > > > > net/net.c:1288:23: error: taking address of packed member of ‘struct
> > > > > ip_udp_hdr’ may result in an unaligned pointer value
> > > > > [-Werror=address-of-packed-member]
> > > > >   1288 |    sumptr = (ushort *)&(ip->udp_src);
> > > > >        |                       ^~~~~~~~~~~~~~
> > > > > 
> > > > > So let's remove the attribute.
> > > > > 
> > > > > Signed-off-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
> > > > > ---
> > > > >   include/net.h | 2 +-
> > > > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/include/net.h b/include/net.h
> > > > > index 75a16e4c8f..bd875b56f5 100644
> > > > > --- a/include/net.h
> > > > > +++ b/include/net.h
> > > > > @@ -390,7 +390,7 @@ struct ip_udp_hdr {
> > > > >       u16        udp_dst;    /* UDP destination port        */
> > > > >       u16        udp_len;    /* Length of UDP packet        */
> > > > >       u16        udp_xsum;    /* Checksum            */
> > > > > -} __attribute__((packed));
> > > > > +};
> > > > > 
> > > > >   #define IP_UDP_HDR_SIZE        (sizeof(struct ip_udp_hdr))
> > > > >   #define UDP_HDR_SIZE        (IP_UDP_HDR_SIZE - IP_HDR_SIZE)
> > > > 
> > > > This came from:
> > > > commit 704f3acfcf55343043bbed01c5fb0a0094a68e8a
> > > > Author: Denis Pynkin <denis.pynkin at collabora.com>
> > > > Date:   Fri Jul 21 19:28:42 2017 +0300
> > > > 
> > > >      net: Use packed structures for networking
> > > > 
> > > >      PXE boot is broken with GCC 7.1 due option '-fstore-merging'
> > > > enabled
> > > >      by default for '-O2':
> > > > 
> > > >      BOOTP broadcast 1
> > > >      data abort
> > > >      pc : [<8ff8bb30>]          lr : [<00004f1f>]
> > > >      reloc pc : [<17832b30>]    lr : [<878abf1f>]
> > > >      sp : 8f558bc0  ip : 00000000     fp : 8ffef5a4
> > > >      r10: 8ffed248  r9 : 8f558ee0     r8 : 8ffef594
> > > >      r7 : 0000000e  r6 : 8ffed700     r5 : 00000000  r4 : 8ffed74e
> > > >      r3 : 00060101  r2 : 8ffed230     r1 : 8ffed706  r0 : 00000ddd
> > > >      Flags: nzcv  IRQs off  FIQs off  Mode SVC_32
> > > >      Resetting CPU ...
> > > > 
> > > >      Core reason is usage of structures for network headers without
> > > > packed
> > > >      attribute.
> > > > 
> > > >      Reviewed-by: Yauheni Kaliuta <yauheni.kaliuta at redhat.com>
> > > >      Signed-off-by: Denis Pynkin <denis.pynkin at collabora.com>
> > > >      Acked-by: Joe Hershberger <joe.hershberger at ni.com>
> > > > 
> > > > ... so adding a few folks to the list and lets see if patchwork picks up
> > > > this tag:
> > > > Fixes: 704f3acfcf55 ("net: Use packed structures for networking")
> > > > 
> > > 
> > > Thanks for providing this background.
> > > 
> > > -fstore-merging is enabled for O2 and Os. But it should not change the
> > > program behavior.
> > > 
> > > The relevant code is in gcc/gimple-ssa-store-merging.c. It has been
> > > completely overhauled since GCC 7.1.
> > > 
> > > I have seen no problems with DHCP, ping and tFTP on arm and arm64 with
> > > GCC 9.2.1.
> > > 
> > > Best regards
> > > 
> > > Heinrich
> > > 
> > > Since GCC 7.1 some bugs have been fixed, e.g.
> > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86492
> > > 
> > 
> > Hello Joe,
> > 
> > how will we carry on, to get the issue resolved?
> > 
> > Best regards
> > 
> > Heinrich
> > _______________________________________________
> 
> Hello Tom, hello Joe,
> 
> I still cannot build sandbox_defconfig. How will we resolve this issue?

We can't drop gcc-7.1 support at this point.  Perhaps use an accessor
function of some sort?

-- 
Tom
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