Suppress "weak external" exports from Mac OS X executables?

[Allen Cronce-2]

Hi all,

We're using boost static libraries in our projects. We've noticed that  
there are tons of symbol exports in our Mac OS X executables, even  
after stripping. Here's an excerpt from an "nm -m" command:

--snip--
00008330 (__TEXT,__text) weak external  
__ZN5boost10filesystem10basic_pathISsNS0_11path_traitsEEdVEPKc
0000c240 (__TEXT,__text) weak external  
__ZN5boost10filesystem22basic_filesystem_errorINS0_10basic_pathISsNS0_11path_traitsEEEEC2ERKSsRKS4_NS_6system10error_codeE
00009d80 (__TEXT,__text) weak external  
__ZN5boost10filesystem22basic_filesystem_errorINS0_10basic_pathISsNS0_11path_traitsEEEED0Ev
00009ef0 (__TEXT,__text) weak external  
__ZN5boost10filesystem22basic_filesystem_errorINS0_10basic_pathISsNS0_11path_traitsEEEED1Ev
0000b340 (__TEXT,__text) weak external  
__ZN5boost15throw_exceptionINS_10filesystem22basic_filesystem_errorINS1_10basic_pathISsNS1_11path_traitsEEEEEEEvRKT_
00008540 (__TEXT,__text) weak external  
__ZN5boost16exception_detail10clone_baseD0Ev
--snip--

Note that these are "defined" externals, meaning the code being  
exported actually exists in the executable section of the binary. I  
would expect to possibly see exported symbols like this in shared  
libraries, but not application executables. In some applications, we  
see hundreds of these exports.

I've tried to suppress these symbols by disabling visibility in the  
boost static libraries, but that hasn't worked. Yes, I'm aware of gcc  
4.0 visibility issues with exception handling across shared libraries.  
But since we're statically linking, we shouldn't see those kind of  
problems.

I suspect that the problem is I'm just not passing the cflags or  
cxxflags correctly. Either that, or this isn't really a symbol  
visibility issue.

In any case, here's the command line I tried:

./tools/jam/src/bin.macosxx86/bjam debug release toolset=darwin  
address-model=32 architecture=combined threading=multi  
link=shared,static macosx-version=10.5 macosx-version-min=10.4 darwin/
cflags=-fvisibility=hidden darwin/cxxflags=-fvisibility=hidden --
layout=system --prefix=/tmp/boostbuild_20081124_142343/32 --exec-
prefix=/tmp/boostbuild_20081124_142343/32 --builddir=../../../
buildProductsMac/boost install

Thanks in advance for any suggestions regarding eliminating these  
symbol exports.

Best,
--
Allen Cronce


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[Juergen Hunold-2]

Hi Allen !

An'n Dienstag 25 November 2008 hett Allen Cronce schreven:

> I suspect that the problem is I'm just not passing the cflags or
> cxxflags correctly.

Most probably.

> Either that, or this isn't really a symbol
> visibility issue.
>
> In any case, here's the command line I tried:
>
> ./tools/jam/src/bin.macosxx86/bjam debug release toolset=darwin
> address-model=32 architecture=combined threading=multi
> link=shared,static macosx-version=10.5 macosx-version-min=10.4 darwin/
> cflags=-fvisibility=hidden darwin/cxxflags=-fvisibility=hidden --

1. simply use cxxflags= , not darwin/cxxflags
2. Use quotes around -fvisibility=hidden else bjam will split again at "="

something like cxxflags=" -fvisibility=hidden" should work.

> layout=system --prefix=/tmp/boostbuild_20081124_142343/32 --exec-
> prefix=/tmp/boostbuild_20081124_142343/32 --builddir=../../../
> buildProductsMac/boost install

add -d+2 or use -n to see the resulting command line. Check this for your
flags.

> Thanks in advance for any suggestions regarding eliminating these
> symbol exports.

Please post the resulting command line next time.

Yours,

Jürgen

--
* Dipl.-Math. Jürgen Hunold       ! Ingenieurgesellschaft für
* voice: ++49 511 262926 57       ! Verkehrs- und Eisenbahnwesen mbH  
* fax  : ++49 511 262926 99       ! Lister Straße 15
* juergen.hunold@...        ! www.ivembh.de
*
* Geschäftsführer:                ! Sitz des Unternehmens: Hannover
* Prof. Dr.-Ing. Thomas Siefer    ! Amtsgericht Hannover, HRB 56965
* PD Dr.-Ing. Alfons Radtke       !
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[Allen Cronce-2]

Hi Jürgen,

Thanks for getting back to me so quickly. Using your suggestions I was  
able to successfully pass the required flags on the command line. Sure  
enough, specifying visibility as hidden disabled the symbol exports in  
our applications. In addition to being cleaner, this also reduces the  
size of the binaries. In one case, I saw a reduction of 22k bytes.

For posterity, here's the build command line that worked:

./tools/jam/src/bin.macosxx86/bjam -d+2 debug release toolset=darwin  
address-model=32 architecture=combined threading=multi link=static  
macosx-version=10.5 macosx-version-min=10.4 cflags="-
fvisibility=hidden -arch x86_64 -arch ppc64" cxxflags="-
fvisibility=hidden -arch x86_64 -arch ppc64" --layout=system --prefix=/
tmp/boostbuild_20081124_142343/32 --exec-prefix=/tmp/
boostbuild_20081124_142343/32 --build-dir=../../../buildProductsMac/
boost install

This results in the correct g++ command lines being generated. Here's  
a sample:

     "g++"  -ftemplate-depth-128 -O3 -finline-functions -Wno-inline -
Wall -mmacosx-version-min=10.4 -no-cpp-precomp -gdwarf-2 -Wno-long-
double -isysroot /Developer/SDKs/MacOSX10.5.sdk -arch i386 -arch ppc -
fvisibility=hidden -arch x86_64 -arch ppc64 -fvisibility=hidden -arch  
x86_64 -arch ppc64 -DBOOST_ALL_NO_LIB=1 -DNDEBUG  -I"." -c -o  
"../../../buildProductsMac/boost/boost/bin.v2/libs/math/build/
darwin-4.0.1/release/address-model-32/architecture-combined/link-
static/macosx-version-min-10.4/macosx-version-10.5/threading-multi/
hypot.o" "libs/math/build/../src/tr1/hypot.cpp"

Although because I'm specifying both cflags and cxxflags, I'm seeing  
two copies of my options on the command line. I guess I should just  
specify cflags instead of both.

As an aside, once I learned how to pass cflags correctly, I was able  
to add 64 bit architectures to the existing 32 bit ones specified via  
the "address-model" option. This allowed me to build quad binaries in  
one pass. Previously our script would build the 32 bit and 64 bit  
binaries separately, then stitch them together with lipo.

Anyway, things look good now. Thanks again for your help Jürgen.

Best,
--
Allen Cronce

On Nov 25, 2008, at 5:24 AM, Jürgen Hunold wrote:

> Hi Allen !
>
> An'n Dienstag 25 November 2008 hett Allen Cronce schreven:
>
>> I suspect that the problem is I'm just not passing the cflags or
>> cxxflags correctly.
>
> Most probably.
>
>> Either that, or this isn't really a symbol
>> visibility issue.
>>
>> In any case, here's the command line I tried:
>>
>> ./tools/jam/src/bin.macosxx86/bjam debug release toolset=darwin
>> address-model=32 architecture=combined threading=multi
>> link=shared,static macosx-version=10.5 macosx-version-min=10.4  
>> darwin/
>> cflags=-fvisibility=hidden darwin/cxxflags=-fvisibility=hidden --
>
> 1. simply use cxxflags= , not darwin/cxxflags
> 2. Use quotes around -fvisibility=hidden else bjam will split again  
> at "="
>
> something like cxxflags=" -fvisibility=hidden" should work.
>
>> layout=system --prefix=/tmp/boostbuild_20081124_142343/32 --exec-
>> prefix=/tmp/boostbuild_20081124_142343/32 --builddir=../../../
>> buildProductsMac/boost install
>
> add -d+2 or use -n to see the resulting command line. Check this for  
> your
> flags.
>
>> Thanks in advance for any suggestions regarding eliminating these
>> symbol exports.
>
> Please post the resulting command line next time.
>
> Yours,
>
> Jürgen
>
> --
> * Dipl.-Math. Jürgen Hunold       ! Ingenieurgesellschaft für
> * voice: ++49 511 262926 57       ! Verkehrs- und Eisenbahnwesen mbH
> * fax  : ++49 511 262926 99       ! Lister Straße 15
> * juergen.hunold@...        ! www.ivembh.de
> *
> * Geschäftsführer:                ! Sitz des Unternehmens: Hannover
> * Prof. Dr.-Ing. Thomas Siefer    ! Amtsgericht Hannover, HRB 56965
> * PD Dr.-Ing. Alfons Radtke       !
> _______________________________________________
> Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost-build

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