bug#24703: Store references in 8-byte chunks in compiled code

[Mark H Weaver]

Mark H Weaver <address@hidden> writes:

> Mark H Weaver <address@hidden> writes:
>
>> Mark H Weaver <address@hidden> writes:
>>
>>> It turns out there's an obfuscated self-reference to fontconfig's store
>>> directory.  Here's an excerpt of the output of "hexdump -C
>>> libfontconfig.so.1.9.0":
>>>
>>> 0000cca0  00 48 b9 2f 67 6e 75 2f  73 74 6f c6 40 48 00 45  
>>> |.H./gnu/address@hidden|
>>> 0000ccb0  31 e4 48 89 08 48 b9 72  65 2f 62 34 38 34 6e 48  
>>> |1.H..H.re/b484nH|
>>> 0000ccc0  89 48 08 48 b9 76 6e 39  6e 6e 72 33 64 48 89 48  
>>> |.H.H.vn9nnr3dH.H|
>>> 0000ccd0  10 48 b9 64 63 6c 70 7a  32 66 6d 48 89 48 18 48  
>>> |.H.dclpz2fmH.H.H|
>>> 0000cce0  b9 61 39 79 78 6d 69 6d  67 48 89 48 20 48 b9 32  |.a9yxmimgH.H 
>>> H.2|
>>> 0000ccf0  6a 6a 2d 66 6f 6e 74 48  89 48 28 48 b9 63 6f 6e  
>>> |jj-fontH.H(H.con|
>>> 0000cd00  66 69 67 2d 32 48 89 48  30 48 b9 2e 31 31 2e 39  
>>> |fig-2H.H0H..11.9|
>>> 0000cd10  34 2f 65 48 89 48 38 48  b9 74 63 2f 66 6f 6e 74  
>>> |4/eH.H8H.tc/font|
>>> 0000cd20  73 48 89 48 40 48 8b 04  24 48 8b 18 48 89 c5 48  |address@hidden|
>>
>> It turns out that this is part of the compiled x86_64 code for
>> 'FcConfigFilename' in src/fccfg.c, which copies a compile-time string
>> constant, 8 bytes at a time, into a buffer:
>>
>> $ objdump -d libfontconfig.so.1.9.0 | grep -B1 -A35 '48 b9 2f 67 6e 75 2f'
>>     cc9b:    0f 84 3f 01 00 00       je     cde0 <FcConfigFilename+0x2d0>
>>     cca1:    48 b9 2f 67 6e 75 2f    movabs $0x6f74732f756e672f,%rcx
>>     cca8:    73 74 6f 
>>     ccab:    c6 40 48 00             movb   $0x0,0x48(%rax)
>>     ccaf:    45 31 e4                xor    %r12d,%r12d
>>     ccb2:    48 89 08                mov    %rcx,(%rax)
>>     ccb5:    48 b9 72 65 2f 62 34    movabs $0x6e343834622f6572,%rcx
>>     ccbc:    38 34 6e 
>>     ccbf:    48 89 48 08             mov    %rcx,0x8(%rax)
>>     ccc3:    48 b9 76 6e 39 6e 6e    movabs $0x6433726e6e396e76,%rcx
>>     ccca:    72 33 64 
>>     cccd:    48 89 48 10             mov    %rcx,0x10(%rax)
>>     ccd1:    48 b9 64 63 6c 70 7a    movabs $0x6d66327a706c6364,%rcx
>>     ccd8:    32 66 6d 
>>     ccdb:    48 89 48 18             mov    %rcx,0x18(%rax)
>>     ccdf:    48 b9 61 39 79 78 6d    movabs $0x676d696d78793961,%rcx
>>     cce6:    69 6d 67 
>>     cce9:    48 89 48 20             mov    %rcx,0x20(%rax)
>>     cced:    48 b9 32 6a 6a 2d 66    movabs $0x746e6f662d6a6a32,%rcx
>>     ccf4:    6f 6e 74 
>>     ccf7:    48 89 48 28             mov    %rcx,0x28(%rax)
>>     ccfb:    48 b9 63 6f 6e 66 69    movabs $0x322d6769666e6f63,%rcx
>>     cd02:    67 2d 32 
>>     cd05:    48 89 48 30             mov    %rcx,0x30(%rax)
>>     cd09:    48 b9 2e 31 31 2e 39    movabs $0x652f34392e31312e,%rcx
>>     cd10:    34 2f 65 
>>     cd13:    48 89 48 38             mov    %rcx,0x38(%rax)
>>     cd17:    48 b9 74 63 2f 66 6f    movabs $0x73746e6f662f6374,%rcx
>>     cd1e:    6e 74 73 
>>     cd21:    48 89 48 40             mov    %rcx,0x40(%rax)
>>     cd25:    48 8b 04 24             mov    (%rsp),%rax
>>     cd29:    48 8b 18                mov    (%rax),%rbx
>>     cd2c:    48 89 c5                mov    %rax,%rbp
>>     cd2f:    48 85 db                test   %rbx,%rbx
>>     cd32:    48 89 df                mov    %rbx,%rdi
>>     cd35:    75 16                   jne    cd4d <FcConfigFilename+0x23d>
>>     cd37:    eb 44                   jmp    cd7d <FcConfigFilename+0x26d>
>>
>> So far, I've not been able to find any evidence of the fontconfig code
>> doing anything strange here.  I strongly suspect that GCC is generating
>> this code, most likely due to an inlinable string/memory copy function
>> where the source is a string literal.
>
> I've confirmed this.  After building this package manually, "objdump -d
> --source src/.libs/fccfg.o" reveals that the corresponding source code
> is:
>
>     dir = (FcChar8 *) FONTCONFIG_PATH;
>     path[i] = malloc (strlen ((char *) dir) + 1);
>     if (!path[i])
>       goto bail1;
>     strcpy ((char *) path[i], (const char *) dir);
>
> It is part of 'FcConfigGetPath', inlined into 'FcConfigFilename', in
> src/fccfg.c.  -DFONTCONFIG_PATH='"$(BASECONFIGDIR)"' is one of the flags
> passed to GCC, via AM_CPPFLAGS in src/Makefile.am.
>
>> Obviously, this could be a serious problem for Guix (and Nix), since it
>> suggests that we may not be able to continue with our simplistic
>> assumption that references to the store in compiled code will be easy to
>> find and replace.

To get an idea of how widespread this problem is, I searched for
occurrences of /gnu/sto[^r] on my GNOME/Xfce desktop system:

$ LC_ALL=C grep '/gnu/sto[^r]' --recursive /gnu/store/
[.../gnu/store/.links hits removed...]
Binary file 
/gnu/store/0010wvgs40kdq8chzsh403qm7la9jxq7-bash-static-4.3.42/bin/bash matches
Binary file /gnu/store/m9vxvhdj691bq1f85lpflvnhcvrdilih-glibc-2.23/sbin/sln 
matches
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/gnu/store/m9vxvhdj691bq1f85lpflvnhcvrdilih-glibc-2.23/lib/libc-2.23.so matches
Binary file /gnu/store/m9vxvhdj691bq1f85lpflvnhcvrdilih-glibc-2.23/lib/libc.a 
matches
Binary file /gnu/store/m9vxvhdj691bq1f85lpflvnhcvrdilih-glibc-2.23/bin/locale 
matches
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/gnu/store/m9vxvhdj691bq1f85lpflvnhcvrdilih-glibc-2.23/bin/localedef matches
Binary file 
/gnu/store/4fs8dg5jhf99xl3ikl093dn1va4wlv79-fontconfig-2.11.94/lib/libfontconfig.so.1.9.0
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/gnu/store/b484nvn9nnr3ddclpz2fma9yxmimg2jj-fontconfig-2.11.94/lib/libfontconfig.so.1.9.0
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/gnu/store/80m11l8km7bwi9iljfyr82hmscaq4xk2-unixodbc-2.3.4/lib/libodbcinst.so.2.0.0
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/gnu/store/80m11l8km7bwi9iljfyr82hmscaq4xk2-unixodbc-2.3.4/lib/libodbc.so.2.0.0 
matches
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/gnu/store/ld16jy012l3jpkj6azynzmldxn28cspw-ncurses-6.0/lib/libncursesw.so.6.0 
matches
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/gnu/store/ld16jy012l3jpkj6azynzmldxn28cspw-ncurses-6.0/lib/libncursesw.a 
matches
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/gnu/store/lxv20br9ic8abvqd7fipszbs4mg8hkjv-ncurses-6.0/lib/libncursesw.so.6.0 
matches
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/gnu/store/lxv20br9ic8abvqd7fipszbs4mg8hkjv-ncurses-6.0/lib/libncursesw.a 
matches
Binary file /gnu/store/frrj3bfbmg5vrd0flh9cf8j64h7cr2v4-gcc-4.9.3/bin/gcc 
matches
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/gnu/store/frrj3bfbmg5vrd0flh9cf8j64h7cr2v4-gcc-4.9.3/bin/x86_64-unknown-linux-gnu-gcc-4.9.3
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/gnu/store/frrj3bfbmg5vrd0flh9cf8j64h7cr2v4-gcc-4.9.3/bin/x86_64-unknown-linux-gnu-c++
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/gnu/store/frrj3bfbmg5vrd0flh9cf8j64h7cr2v4-gcc-4.9.3/bin/x86_64-unknown-linux-gnu-gcc
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/gnu/store/frrj3bfbmg5vrd0flh9cf8j64h7cr2v4-gcc-4.9.3/bin/x86_64-unknown-linux-gnu-g++
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matches
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/gnu/store/sxa3b6l28ckcnyg3g7f4brvl2rdpncy1-gnuplot-5.0.4-1/bin/gnuplot matches
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/gnu/store/2jvvwqz16hj2c5ws0xa46x98fvl9m90m-fontconfig-2.11.94/lib/libfontconfig.so.1.9.0
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/gnu/store/bxy1hwriqzdw6xk7bl28qfsw4s1s5xdq-bash-static-4.3.48/bin/bash matches
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/gnu/store/3chnjjkazbv0fqbshrwahq7c3zfg42s8-ncurses-6.0/lib/libncursesw.so.6.0 
matches
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/gnu/store/3chnjjkazbv0fqbshrwahq7c3zfg42s8-ncurses-6.0/lib/libncursesw.a 
matches
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/gnu/store/my7f7fq2ca5rqq4wyyrg20cw2bjrj2l4-ncurses-6.0/lib/libncursesw.so.6.0 
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/gnu/store/my7f7fq2ca5rqq4wyyrg20cw2bjrj2l4-ncurses-6.0/lib/libncursesw.a 
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Binary file /gnu/store/dmz9v8bmxd3davz77s4b10pmpmjnv98a-gcc-4.9.3/bin/gcc 
matches
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/gnu/store/dmz9v8bmxd3davz77s4b10pmpmjnv98a-gcc-4.9.3/bin/x86_64-unknown-linux-gnu-gcc-4.9.3
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/gnu/store/dmz9v8bmxd3davz77s4b10pmpmjnv98a-gcc-4.9.3/bin/x86_64-unknown-linux-gnu-c++
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/gnu/store/dmz9v8bmxd3davz77s4b10pmpmjnv98a-gcc-4.9.3/bin/x86_64-unknown-linux-gnu-gcc
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Binary file /gnu/store/dmz9v8bmxd3davz77s4b10pmpmjnv98a-gcc-4.9.3/bin/g++ 
matches
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/gnu/store/dmz9v8bmxd3davz77s4b10pmpmjnv98a-gcc-4.9.3/bin/x86_64-unknown-linux-gnu-g++
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Binary file /gnu/store/dmz9v8bmxd3davz77s4b10pmpmjnv98a-gcc-4.9.3/bin/cpp 
matches
Binary file /gnu/store/dmz9v8bmxd3davz77s4b10pmpmjnv98a-gcc-4.9.3/bin/c++ 
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/gnu/store/fjsaprcdmdn39pk39jrhbby1jl5i8rp5-xorg-server-1.18.1/bin/Xorg matches
Binary file /gnu/store/mz301kb7wqvyl9kxil4bpn8ng99ikgqy-glibc-2.23/sbin/sln 
matches
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/gnu/store/mz301kb7wqvyl9kxil4bpn8ng99ikgqy-glibc-2.23/lib/libc-2.23.so matches
Binary file /gnu/store/mz301kb7wqvyl9kxil4bpn8ng99ikgqy-glibc-2.23/lib/libc.a 
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Binary file /gnu/store/mz301kb7wqvyl9kxil4bpn8ng99ikgqy-glibc-2.23/bin/locale 
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/gnu/store/mz301kb7wqvyl9kxil4bpn8ng99ikgqy-glibc-2.23/bin/localedef matches
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/gnu/store/slhwk75g7d8bywpq2hifs7g9fxr6jx3d-bash-static-4.3.48/bin/bash matches
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/gnu/store/qjsmp5s85qrba18fxf319m5lv7f8awf8-graphviz-2.38.0/bin/lefty matches
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/gnu/store/6ddfp4pwlrxc5jdgf17ddh4m5wi1cldy-xorg-server-1.18.1/bin/Xorg matches
Binary file /gnu/store/zav1zqwmzzz5xk71v22i7n6qidwh49in-gcc-4.9.3/bin/gcc 
matches
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/gnu/store/zav1zqwmzzz5xk71v22i7n6qidwh49in-gcc-4.9.3/bin/x86_64-unknown-linux-gnu-gcc-4.9.3
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/gnu/store/zav1zqwmzzz5xk71v22i7n6qidwh49in-gcc-4.9.3/bin/x86_64-unknown-linux-gnu-c++
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/gnu/store/zav1zqwmzzz5xk71v22i7n6qidwh49in-gcc-4.9.3/bin/x86_64-unknown-linux-gnu-gcc
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Binary file /gnu/store/zav1zqwmzzz5xk71v22i7n6qidwh49in-gcc-4.9.3/bin/g++ 
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/gnu/store/zav1zqwmzzz5xk71v22i7n6qidwh49in-gcc-4.9.3/bin/x86_64-unknown-linux-gnu-g++
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Binary file /gnu/store/zav1zqwmzzz5xk71v22i7n6qidwh49in-gcc-4.9.3/bin/cpp 
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Binary file /gnu/store/zav1zqwmzzz5xk71v22i7n6qidwh49in-gcc-4.9.3/bin/c++ 
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/gnu/store/xl19qrfzga52vrvp4ncccwjlnrjqwj95-ncurses-6.0/lib/libncursesw.so.6.0 
matches
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/gnu/store/xl19qrfzga52vrvp4ncccwjlnrjqwj95-ncurses-6.0/lib/libncursesw.a 
matches
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/gnu/store/kh3awka9xslyp52dldb3gma47rr0kp2x-xorg-server-1.18.1/bin/Xorg matches
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/gnu/store/121596cgx25s8zcl3yznyh2vh1f842ni-babl-0.1.18/lib/libbabl-0.1.so.0.117.1
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/gnu/store/srfjnfkmjkc4xcld311xsdvhng08mmpi-gcc-6.2.0/bin/x86_64-unknown-linux-gnu-gcc-6.2.0
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/gnu/store/srfjnfkmjkc4xcld311xsdvhng08mmpi-gcc-6.2.0/bin/x86_64-unknown-linux-gnu-c++
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/gnu/store/srfjnfkmjkc4xcld311xsdvhng08mmpi-gcc-6.2.0/bin/x86_64-unknown-linux-gnu-gcc
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/gnu/store/srfjnfkmjkc4xcld311xsdvhng08mmpi-gcc-6.2.0/bin/x86_64-unknown-linux-gnu-g++
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/gnu/store/j4q20kwzd5g1d3gv419692k66ghfzymz-gnuplot-5.0.4-1/bin/gnuplot matches
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/gnu/store/mdc84lh0mfzw9n404cnzi9l1l8qr7a4r-gnuplot-5.0.4-1/bin/gnuplot matches
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/gnu/store/8mj5yd1z936j64sdpx3hbqi3qkdif0c4-alsa-lib-1.0.27.1/lib/libasound.so.2.0.0
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/gnu/store/ninvaqcyhm6s11yp97m17h2i1q3aj24s-recode-3.7.0.201402/lib/librecode.a 
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/gnu/store/ninvaqcyhm6s11yp97m17h2i1q3aj24s-recode-3.7.0.201402/lib/librecode.so.0.0.0
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/gnu/store/kjybzn7az86n1qzxcm8zdz2gaypp4az6-fontconfig-2.11.94/lib/libfontconfig.so.1.9.0
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/gnu/store/cl2vwkvmk60s7vpamivpclzgyfxlb7wx-graphviz-2.38.0/bin/lefty matches
Binary file /gnu/store/qc8qg71k1b7gizqxa785c6ls71i8qk6d-units-2.13/bin/units 
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/gnu/store/sj8ygx2yz58hn1142yjjsb34sql4b9xr-unixodbc-2.3.4/lib/libodbcinst.so.2.0.0
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/gnu/store/sj8ygx2yz58hn1142yjjsb34sql4b9xr-unixodbc-2.3.4/lib/libodbc.so.2.0.0 
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/gnu/store/571c58j8f06x8svykg4n5s0ip36kna5c-util-linux-2.27/lib/libuuid.so.1.3.0
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/gnu/store/1i3xmm18dw9kq6wi46f6sj9nxy9pckjl-alsa-lib-1.0.27.1/lib/libasound.so.2.0.0
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/gnu/store/x1kh4kkifc3f4gnlwvfgk53fm2zhfhmm-gnuplot-5.0.4-1/bin/gnuplot matches
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/gnu/store/fnw55giyr1gnqyyw5yx4hf96mlrkp603-gnuplot-5.0.4-1/bin/gnuplot matches
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/gnu/store/mj727bz0l8afmn97l8gsc5wh30jnql8s-babl-0.1.18/lib/libbabl-0.1.so.0.117.1
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/gnu/store/0m908gszml9bb6vkikbzdqpslah2a1db-gcc-6.2.0/bin/x86_64-unknown-linux-gnu-gcc-6.2.0
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Binary file /gnu/store/0m908gszml9bb6vkikbzdqpslah2a1db-gcc-6.2.0/bin/gcc 
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/gnu/store/0m908gszml9bb6vkikbzdqpslah2a1db-gcc-6.2.0/bin/x86_64-unknown-linux-gnu-c++
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/gnu/store/0m908gszml9bb6vkikbzdqpslah2a1db-gcc-6.2.0/bin/x86_64-unknown-linux-gnu-gcc
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/gnu/store/0m908gszml9bb6vkikbzdqpslah2a1db-gcc-6.2.0/bin/x86_64-unknown-linux-gnu-g++
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/gnu/store/lqybibdq19q6ypm29p9p9s9ns0s66n0b-recode-3.7.0.201402/lib/librecode.a 
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/gnu/store/lqybibdq19q6ypm29p9p9s9ns0s66n0b-recode-3.7.0.201402/lib/librecode.so.0.0.0
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/gnu/store/pxdl28wbikj2jy0jjldmii245gcsh5fq-fontconfig-2.11.94/lib/libfontconfig.so.1.9.0
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/gnu/store/cji1mwp7n6zhdnpg73gighf3fvrh2gdi-ncurses-6.0/lib/libncursesw.so.6.0 
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/gnu/store/cji1mwp7n6zhdnpg73gighf3fvrh2gdi-ncurses-6.0/lib/libncursesw.a 
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/gnu/store/1rcsqn8h2xwmgdra3zr33xv73d44wf1s-fontconfig-2.11.94/lib/libfontconfig.so.1.9.0
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/gnu/store/iiakyhsw889rvv3ghk6jl3mfdrs1wfan-fontconfig-2.11.94/lib/libfontconfig.so.1.9.0
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/gnu/store/zb3kh929v8yhkyg3sn8405zj4x49aza4-gnuplot-5.0.4-1/bin/gnuplot matches
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/gnu/store/mkq7h60l1kx4hjclsrd0nbz8v4mnx4lv-gnuplot-5.0.4-1/bin/gnuplot matches
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/gnu/store/4vhgx5xkbx0x7gnph9fq3c581rnj5ynq-libgphoto2-2.5.2/lib/libgphoto2/2.5.2/konica.so
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/gnu/store/r6kwxzban57ghxsy8p8dqjvym6vnb2nz-graphviz-2.38.0/bin/lefty matches
/gnu/store/lwxifldgdyyzd83510nzf1qffpzxbdyl-guix-0.11.0-1.4420/share/guile/site/2.0/gnu/packages/package-management.scm:
              (uri (string-append "mirror://gnu/stow/stow-"
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/gnu/store/zslzcw2wg6xylwwr9hcx2sbal0bm6kjx-util-linux-2.27/lib/libuuid.so.1.3.0
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