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Message-ID: <20160524232129.GN21636@brightrain.aerifal.cx>
Date: Tue, 24 May 2016 19:21:29 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: sockaddr_storage and GCC 6.1
On Tue, May 24, 2016 at 06:55:48PM -0400, Rich Felker wrote:
> On Tue, May 24, 2016 at 06:36:02PM -0400, Rich Felker wrote:
> > On Tue, May 24, 2016 at 03:07:35PM -0700, William Ahern wrote:
> > > GCC 6.1 more aggressively decomposes aggregate assignments into a series of
> > > scalar member assignments. This has uncovered an issue with glibc's layout
> > > of struct sockaddr_storage, which has a padding hole from offsets 2 to 8,
> > > precisely where .sin_port and .sin_addr are in struct sockaddr_in.
> > >
> > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71120
> > >
> > > musl shares this same issue. Specifically, the __ss_align member with an
> > > 8-byte alignment on LP64 archs. You can track the glibc resolution at
> > >
> > > https://sourceware.org/bugzilla/show_bug.cgi?id=20111
> > >
> > > Or not track it. Reasonable folks can disagree regarding many aspects of
> > > this issue, but I thought it worthwhile to bring to people's attention.
> >
> > I maintain that it's a bug (violation of effective type rules) for a
> > program to attempt to copy sockaddr types using sockaddr_storage, but
> > this is a nasty application bug to track down (usually silent
> > breakage) that's worth avoiding since it's easy. Does the attached
> > patch work?
> >
> > I don't think we should even consider the sorts of may_alias hacks
> > glibc/gcc folks are discussing, though. There's already a gcc option
> > for compiling broken code like that; it's called -fno-strict-aliasing.
> >
> > Rich
>
> > diff --git a/include/sys/socket.h b/include/sys/socket.h
> > index 6788375..d2bd5df 100644
> > --- a/include/sys/socket.h
> > +++ b/include/sys/socket.h
> > @@ -286,7 +286,7 @@ struct sockaddr
> >
> > struct sockaddr_storage
> > {
> > - sa_family_t ss_family;
> > + sa_family_t ss_family, __ss_family_pad;
> > unsigned long __ss_align;
> > char __ss_padding[128-2*sizeof(unsigned long)];
> > };
>
> This is wrong for 64-bit archs; new version attached.
>
> Rich
> diff --git a/include/sys/socket.h b/include/sys/socket.h
> index 6788375..c7f244a 100644
> --- a/include/sys/socket.h
> +++ b/include/sys/socket.h
> @@ -287,6 +287,7 @@ struct sockaddr
> struct sockaddr_storage
> {
> sa_family_t ss_family;
> + char __ss_family_pad[sizeof(long)-sizeof(sa_family_t)];
> unsigned long __ss_align;
> char __ss_padding[128-2*sizeof(unsigned long)];
> };
And here's a potentially simpler version.
Rich
View attachment "sockaddr_storage_v3.diff" of type "text/plain" (403 bytes)
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