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From: =?UTF-8?Q?Johan_Bolmsj=C3=B6?= <johan.bolmsjo@gmail.com>
Newsgroups: gnu.utils.bug
Subject: Re: GNU ld: Uninitialized variables with "-Wl, --exclude-libs, ALL" global
Date: Mon, 31 Aug 2015 10:14:34 +0200
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Approved: bug-gnu-utils@gnu.org
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Sorry, it seems I found the wrong mailing list for reporting GNU ld bugs
(obsolete information obtained using google).

I will send the mail to the binutils bug mailing list.



On Mon, Aug 31, 2015 at 10:04 AM, Johan Bolmsj=C3=B6 <johan.bolmsjo@gmail.c=
om>
wrote:

> Hello,
>
> I'm building a shared library using a bunch of static libraries. The
> shared library is linked using the option "-Wl,--exclude-libs,ALL".
> According to the documentation this option should prevent all symbols in
> the static libraries from being exported. I have found this to be true fo=
r
> functions and initialized variables. Uninitialized variables however, e.g=
.
> a global variable "int foo;" are still global in the resulting shared
> library. The gold linker behaves according to the documentation and
> uninitialized variables are local in the resulting shared library. I.e.
> there is a difference in behaviour between GNU ld and GNU gold linker.
> *--exclude-libs* *lib**,**lib**,...* Specifies a list of archive
> libraries from which symbols should not be automatically exported.gcc
> -Wl,--version
> collect2 version 4.9.2
> /usr/bin/ld -plugin /usr/lib/gcc/x86_64-linux-gnu/4.9/liblto_plugin.so
> -plugin-opt=3D/usr/lib/gcc/x86_64-linux-gnu/4.9/lto-wrapper
> -plugin-opt=3D-fresolution=3D/tmp/ccannlod.res -plugin-opt=3D-pass-throug=
h=3D-lgcc
> -plugin-opt=3D-pass-through=3D-lgcc_s -plugin-opt=3D-pass-through=3D-lc
> -plugin-opt=3D-pass-through=3D-lgcc -plugin-opt=3D-pass-through=3D-lgcc_s
> --sysroot=3D/ --build-id --eh-frame-hdr -m elf_x86_64 --hash-style=3Dgnu
> -dynamic-linker /lib64/ld-linux-x86-64.so.2
> /usr/lib/gcc/x86_64-linux-gnu/4.9/../../../x86_64-linux-gnu/crt1.o
> /usr/lib/gcc/x86_64-linux-gnu/4.9/../../../x86_64-linux-gnu/crti.o
> /usr/lib/gcc/x86_64-linux-gnu/4.9/crtbegin.o
> -L/usr/lib/gcc/x86_64-linux-gnu/4.9
> -L/usr/lib/gcc/x86_64-linux-gnu/4.9/../../../x86_64-linux-gnu
> -L/usr/lib/gcc/x86_64-linux-gnu/4.9/../../../../lib -L/lib/x86_64-linux-g=
nu
> -L/lib/../lib -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib
> -L/usr/lib/gcc/x86_64-linux-gnu/4.9/../../.. --version -lgcc --as-needed
> -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed
> /usr/lib/gcc/x86_64-linux-gnu/4.9/crtend.o
> /usr/lib/gcc/x86_64-linux-gnu/4.9/../../../x86_64-linux-gnu/crtn.o
> GNU ld (GNU Binutils for Debian) 2.25
> Copyright (C) 2014 Free Software Foundation, Inc.
> This program is free software; you may redistribute it under the terms of
> the GNU General Public License version 3 or (at your option) a later
> version.
> This program has absolutely no warranty.
>
> I'm using Debian 8 and this is the Debian gcc package. They may have
> applied patches for binutils, but probably nothing that should explain th=
is
> behaviour.
>
> The following script illustrates the issue.
> It's simple enough to be an instruction about what commands to run.
> The script does not need to be executed if there are concerns about its
> safety.
>
> #!/bin/bash
>
> set -ve
>
> TMP_C=3D"tmp.$$.c"
> TMP_O=3D"tmp.$$.o"
> TMP_A=3D"libtmp.$$.a"
> TMP_GNU_SO=3D"libtmp.$$.gnu.so"
> TMP_GOLD_SO=3D"libtmp.$$.gold.so"
>
> cleanup() {
>     rm -f $TMP_C $TMP_O $TMP_A $TMP_GNU_SO $TMP_GOLD_SO
> }
> trap cleanup EXIT
>
> cat > $TMP_C <<EOF
> int foo;
> int bar =3D 42;
> EOF
>
> # Create static library with two global symbols.
> gcc -g3 -Wall -c $TMP_C -o $TMP_O
> rm -f $TMP_A
> ar rcs $TMP_A $TMP_O
>
> # Create a sharerd library with "-Wl,--exclude-libs,ALL" and the GNU ld
> linker.
> gcc -shared -Wl,-soname,libtmp.so.1 -o $TMP_GNU_SO -Wl,--exclude-libs,ALL
> -L. -Wl,--whole-archive -ltmp.$$ -Wl,--no-whole-archive
>
> # Create a sharerd library with "-Wl,--exclude-libs,ALL" and the GNU gold
> linker.
> gcc -fuse-ld=3Dgold -shared -Wl,-soname,libtmp.so.1 -o $TMP_GOLD_SO
> -Wl,--exclude-libs,ALL -L. -Wl,--whole-archive -ltmp.$$
> -Wl,--no-whole-archive
>
> # Show the result.
>
> echo "### GNU ld global symbols"
> nm -D $TMP_GNU_SO
>
> echo "### GNU gold global symbols"
> nm -D $TMP_GOLD_SO
>
>
> # Script in uuencoded form
> begin 644 -
> M(R$O8FEN+V)A<V@*"G-E=3D"`M=3DF4*"E1-4%]#/2)T;7`N)"0N8R(*5$U07T\]
> M(G1M<"XD)"YO(@I435!?03TB;&EB=3D&UP+B0D+F$B"E1-4%]'3E5?4T\](FQI
> M8G1M<"XD)"YG;G4N<V\B"E1-4%]'3TQ$7U-//2)L:6)T;7`N)"0N9V]L9"YS
> M;R(*"F-L96%N=3D7`H*2!["B`@("!R;2`M9B`D5$U07T,@)%1-4%]/("1435!?
> M02`D5$U07T=3D.55]33R`D5$U07T=3D/3$1?4T\*?0IT<F%P(&-L96%N=3D7`@15A)
> M5`H*8V%T(#X@)%1-4%]#(#P\14]&"FEN=3D"!F;V\["FEN=3D"!B87(@/2`T,CL*
> M14]&"@HC($-R96%T92!S=3D&%T:6,@;&EB<F%R>2!W:71H('1W;R!G;&]B86P@
> M<WEM8F]L<RX*9V-C("UG,R`M5V%L;"`M8R`D5$U07T,@+6\@)%1-4%]/"G)M
> M("UF("1435!?00IA<B!R8W,@)%1-4%]!("1435!?3PH*(R!#<F5A=3D&4@82!S
> M:&%R97)D(&QI8G)A<GD@=3DVET:"`B+5=3DL+"TM97AC;'5D92UL:6)S+$%,3"(@
> M86YD('1H92!'3E4@;&0@;&EN:V5R+@IG8V,@+7-H87)E9"`M5VPL+7-O;F%M
> M92QL:6)T;7`N<V\N,2`M;R`D5$U07T=3D.55]33R`M5VPL+2UE>&-L=3D61E+6QI
> M8G,L04Q,("U,+B`M5VPL+2UW:&]L92UA<F-H:79E("UL=3D&UP+B0D("U7;"PM
> M+6YO+7=3DH;VQE+6%R8VAI=3DF4*"B,@0W)E871E(&$@<VAA<F5R9"!L:6)R87)Y
> M('=3DI=3D&@@(BU7;"PM+65X8VQU9&4M;&EB<RQ!3$PB(&%N9"!T:&4@1TY5(&=3DO
> M;&0@;&EN:V5R+@IG8V,@+69U<V4M;&0]9V]L9"`M<VAA<F5D("U7;"PM<V]N
> M86UE+&QI8G1M<"YS;RXQ("UO("1435!?1T],1%]33R`M5VPL+2UE>&-L=3D61E
> M+6QI8G,L04Q,("U,+B`M5VPL+2UW:&]L92UA<F-H:79E("UL=3D&UP+B0D("U7
> M;"PM+6YO+7=3DH;VQE+6%R8VAI=3DF4*"B,@4VAO=3DR!T:&4@<F5S=3D6QT+@H*96-H
> M;R`B(R,C($=3D.52!L9"!G;&]B86P@<WEM8F]L<R(*;FT@+40@)%1-4%]'3E5?
> M4T\*"F5C:&\@(B,C(R!'3E4@9V]L9"!G;&]B86P@<WEM8F]L<R(*;FT@+40@
> -)%1-4%]'3TQ$7U-/"@``
> `
> end
>
>
>
> Script output:
>
> ### GNU ld global symbols
> 000000000020088c B __bss_start
>                  w __cxa_finalize
> 000000000020088c D _edata
> 0000000000200898 B _end
> 0000000000000630 T _fini
> *0000000000200890 B foo*
>                  w __gmon_start__
> 00000000000004d8 T _init
>                  w _ITM_deregisterTMCloneTable
>                  w _ITM_registerTMCloneTable
>                  w _Jv_RegisterClasses
>
> ### GNU gold global symbols
> 0000000000001968 A __bss_start
>                  w __cxa_finalize
> 0000000000001968 A _edata
> 0000000000001970 A _end
> 0000000000000680 T _fini
>                  w __gmon_start__
> 0000000000000528 T _init
>                  w _ITM_deregisterTMCloneTable
>                  w _ITM_registerTMCloneTable
>                  w _Jv_RegisterClasses
>
>