armv7, building p7zip and -fPIC

[Ian Lepore]

On Sat, 2017-10-07 at 13:15 -0700, Warner Losh wrote:
> On Sat, Oct 7, 2017 at 12:09 PM, Ian Lepore <ian at freebsd.org> wrote:
> 
> > 
> > On Sat, 2017-10-07 at 21:59 +0300, Guy Yur wrote:
> > > 
> > > On 7 October 2017 at 21:40, Warner Losh <imp at bsdimp.com> wrote:
> > > > 
> > > > 
> > > > 
> > > > 
> > > > On Sat, Oct 7, 2017 at 11:24 AM, Guy Yur <guyyur at gmail.com>
> > > > wrote:
> > > > > 
> > > > > 
> > > > > 
> > > > > Hi,
> > > > > 
> > > > > Does armv7 need -fPIC when compiling?
> > > > > 
> > > > > Building archivers/p7zip fails with:
> > > > > /usr/bin/ld: 7zEncode.o(.text+0x2d04): unresolvable
> > > > > R_ARM_MOVW_ABS_NC
> > > > > relocation against symbol `_ZTIi@@CXXABI_1.3'
> > > > > /usr/bin/ld: final link failed: Nonrepresentable section on
> > > > > output
> > > > > c++: error: linker command failed with exit code 1 (use -v to
> > > > > see
> > > > > invocation)
> > > > > *** [../../../../bin/7z.so] Error code 1
> > > > > 
> > > > > make[3]: stopped in
> > > > > 
> > > > > /usr/wrkdir/usr/ports/archivers/p7zip/work/p7zip_16.
> > 02/CPP/7zip/Bundles/Format7zFree
> > > 
> > > > 
> > > > > 
> > > > > 1 error
> > > > > 
> > > > > If I add "CFLAGS_armv7= -fPIC" in the port Makefile it builds
> > > > > fine.
> > > > > The port has -fPIC for aarch64, amd64, powerpc and sparc64.
> > > > > 
> > > > > Is it a difference from armv6?
> > > > > When I previously built for armv6 it worked without the
> > > > > option.
> > > > armv7 is new in FreeBSD (two days old), and maybe you are
> > > > tripping over
> > > > something inside the port that optimized for it? Is there a
> > > > CFLAGS+armv6=-fPIC? I don't see it with a quick grep, but you
> > > > never
> > know...
> > > 
> > > > 
> > > > If that's what it takes to fix it, maybe you should submit that
> > > > to the
> > port
> > > 
> > > > 
> > > > maintainer?
> > > > 
> > > > Warner
> > > Hi,
> > > 
> > > Seems to indeed be a difference between armv6 and armv7,
> > > found this: https://bugs.launchpad.net/ubuntu/+source/gcc-4.4/+bu
> > > g/
> > 503448
> > > 
> > > 
> > > I will submit a patch to the port maintainer to add CFLAGS for
> > > armv7.
> > > 
> > > Thanks,
> > > Guy
> > This is really not just an armv7-only thing, the -fPIC flag should
> > always be used.  On armv6 (and some other non-arm arches) it will
> > accidentally work without that flag, but that doesn't make it
> > right.
> > 
> I've emailed the maintainer asking to apply this:
> diff --git a/archivers/p7zip/Makefile b/archivers/p7zip/Makefile
> index 9e2c2a21deec..1bf32ccd39ac 100644
> --- a/archivers/p7zip/Makefile
> +++ b/archivers/p7zip/Makefile
> @@ -20,6 +20,8 @@ MAKEFILE=     makefile
>  MAKE_ARGS=     OPTFLAGS="${CXXFLAGS}"
>  WRKSRC=                ${WRKDIR}/${PORTNAME}_${PORTVERSION}
> 
> +CFLAGS_arm=    -fPIC
> +CFLAGS_armv6=  -fPIC
>  CFLAGS_armv7=  -fPIC
>  CFLAGS_aarch64=        -fPIC
>  CFLAGS_amd64=  -fPIC
> 
> Warner

But why not just CFLAGS+= -fPIC ?  Text-segment relocations triggering
COW on shared text pages aren't any better in a powerpc or i386 shared
lib than arm, right?

-- Ian