How can I force the gcc linker to link against a given version (soname) of a shared library on the system?
I need this to enforce that the version of openssl that is #include'ed matches the version that is linked, on any system, even if multiple versions of openssl are installed. To find the ABI version, my configure script first compiles and runs a program that extracts the SONAME from the headers:
#include <openssl/opensslv.h>
#include <stdio.h>
int main () {
printf(SHLIB_VERSION_NUMBER);
return 0;
}
The SHLIB_VERSION_NUMBER contains the so version string, e.g. 0.9.8 or 1.0.2k or 1.1.0. But how do I tell gcc to link against this version of libssl or libcrypto rather than just any -lssl?
I tried "in situ" linking, so that instead of linking with gcc main.c -lcrypto we use:
gcc main.c libcrypto.so.1.1.0
However it seems the linker libcrypto.so.1.1.0 cannot be found:
gcc: error: libcrypto.so.1.1.0: No such file or directory
I guess the system only searches in the standard locations when using the -l flag. Is there a better way to make my software link against libcrypto.so.1.1.0?
To select the correct version of the openssl shared libraries use:
gcc main.c -l:libssl.so.1.0.0 -l:libcrypto.so.1.0.0
The key to answering this question is "how do I control ld so that is links the correct version of a shared library?".
The correct way to pass a linker flag (a command line parameter to ld) using the gnu compilers (gcc, g++, gdc, etc...) is to use the normal ld parameter prefixed with "-l". For example -lssl or -L/usr/local/lib.
Edit: As per How to specify the library version to use at link time? you can read the manual for ld with:man ld.
Related
My system is an older NAS running 2.6.32. I have found that when using -static for any subsequent library, it will also try to statically link any other library that I might need.
When I add the -Wl,-Bdynamic flag first and then explicitly name those libraries using -lc, such as "-Wl,-Bdynamic -lc -lstdc++" then it works. So what happens is that libc and others fail to be statically linked.
The static libc on the system is called /opt/lib/libc_nonshared.a.
The contents of /opt/lib/libc.so is this:
OUTPUT_FORMAT(elf32-littlearm)
GROUP ( /lib/libc.so.6 /opt/lib/libc_nonshared.a )
The gcc version is 4.2.3. The current build command I am facing adds -dynamic at the end but this doesn't help much. When I add some static library directly using its .a name, and not using a -l flag, then there is no issue.
The problem seems to be that the dynamic library of libc came with the NAS, but the static version sits in /opt/lib.
I run:
gcc hamming.c -static -L. -L/opt/lib -l:matrix.a -o hamming
I get:
/opt/lib/gcc/arm-none-linux-gnueabi/4.2.3/../../../../arm-none-linux-gnueabi/bin/ld: cannot find -lc
collect2: ld returned 1 exit status
make: *** [hamming] Error 1
when I try to use static libc as is. Were I to perform a 'hack' to link libc_nonshared.a to libc.a, it suddenly does find it. But complains:
hamming.c:54: undefined reference to `malloc'
hamming.c:54: undefined reference to `memset'
And a zillion other errors of course. As mentioned above, /opt/libc.so contains the reference to both files (dynamic and static).
For libstdc++ only a .la file exists.
The -static linker flag does not take any argument. It is a boolean
flag that simply directs the linker to link no shared libraries, as
documented
-static
Do not link against shared libraries...
There is no need to explicitly direct the linker to link shared (dynamic)
libraries when it has a choice because that is the default bevaiour. If
you simply link, e.g.
gcc -o prog ... -lfoo ...
then the linker will link the first of libfoo.so (shared) or libfoo.a
(static) that it finds in any of the specified (-Ldir) or default
search directories, searched in commandline sequence. If it finds both
libfoo.so and libfoo.a in the same directory then it will choose
libfoo.so. Thus shared and static libraries may be freely intermixed
without any special options.
Specify -static only if you wish to link only static libraries.
If you wish to insist on linking a particular libfoo.a even when
libfoo.so is in the same directory and would be chosen by default,
use the explicit form of the -l option: -l:libfoo.a
Later
gcc hamming.c -static -L. -L/opt/lib -l:matrix.a -o hamming
This command is failing with:
ld: cannot find -lc
because the linker (ld) cannot find a static library libc.a in
any of the specified linker search directories (-L. -L/opt/lib) or
the default linker search directories. If you wish instead to link
/opt/lib/libc_nonshared.a then your command should be:
>gcc hamming.c -static -L. -L/opt/lib -l:matrix.a -lc_nonshared -o hamming
However, you have not explained why you want to link this program statically
(-static) in the first place, which is not the usual way and will require you to have installed
static versions of all libraries required for the linkage - both those
you explicitly link and the default libraries that gcc will add for C language
linkage (Standard C library, GCC runtime library).
Supposing you have a static library called (oddly) matrix.a (rather
than normally, libmatrix.a) that is located in /some/dir/, then the
normal way to compile and link your program would be:
gcc hamming.c -L/some/dir -l:matrix.a -o hamming
I suggest you start with that and deviate only as problems compel
you to.
The discovery of an /opt/lib/libc.so containing:
OUTPUT_FORMAT(elf32-littlearm)
GROUP ( /lib/libc.so.6 /opt/lib/libc_nonshared.a )
is misleading you. This is not your shared libc. A shared library
is a binary. This is a linker script, and it says that your shared libc
is in fact /lib/libc.so.6. The linker will almost certainly find and use it by default.
-lc links with libc, but -m will specify whether it should be 32 or 64bit.
My question is, does gcc or ld decide which libc.so should be the correct library to link with?
Thanks!
Just compile something using GCC and add verbosity options. You'll then see that gcc passes the libc path to LD. GCC has the path hard-coded in, but it can be overridden with some -W parameter.
Note that LD obviously still needs to know if it is to generate a 32-bit or 64-bit binary, but the libc path doesn't come from -m but is passed separately.
I am trying to link my program statically with glibc, because version of the glibc on the target machine is pretty much unpredictable. I used linker flags -static-libgcc and -static-libstdc++ and it worked fine. The executable is big, but I can live with it. Unfortunately, when I run my executable on the target machine (it is named 'mytest' in the example below) I get the following error:
./mytest: /usr/lib64/libstdc++.so.6: version `GLIBCXX_3.4.11' not found (required by libboost_log.so.1.53.0)
./mytest: /usr/lib64/libstdc++.so.6: version `GLIBCXX_3.4.15' not found (required by libboost_log.so.1.53.0)
./mytest: /usr/lib64/libstdc++.so.6: version `GLIBCXX_3.4.9' not found (required by libboost_log.so.1.53.0)
./mytest: /usr/lib64/libstdc++.so.6: version `GLIBCXX_3.4.15' not found (required by libboost_date_time.so.1.53.0)
./mytest: /usr/lib64/libstdc++.so.6: version `GLIBCXX_3.4.9' not found (required by libboost_thread.so.1.53.0)
If I do 'strings' on mytest, it gives me
$ strings mytest | grep GLIBC
GLIBC_2.9
GLIBC_2.7
GLIBC_2.8
GLIBC_2.3.2
GLIBC_2.2.5
GLIBCXX_3.4.15
GLIBCXX_3.4.11
GLIBCXX_3.4.14
GLIBCXX_3.4.9
GLIBCXX_3.4
What means, I think, that the static linking was working ok. Why does the loader still tries to look for my functions in shared glibc and libstdc++? What am I doing wrong?
Thanks!
I am trying to link my program statically with glibc, because version of the glibc on the target machine is pretty much unpredictable. I used linker flags -static-libgcc and -static-libstdc++ and it worked fine.
That didn't affect the version of glibc (libc), which is different from libgcc and libstdc++. With these flags, you still have produced a dynamically-linked executable, which is expected to not work on an older distribution.
You can link your executable with -static flag, and that should give you a completely static executable.
Update:
After re-reading your question; your problem is not with glibc. Your problem is that you are linking with libboost_log.so, which itself depends on libstdc++.so.6.
The answer then is to link with libboost*.a instead of libboost*.so. You can try to achieve it this way:
g++ $(OBJS) -static-libgcc -static-libstdc++ -Wl,-Bstatic -lboost_log ... \
-Wl,-Bdynamic
(It is very important to have the trailing -Wl,-Bdynamic.)
Linking with -static-libgcc and -static-libstdc++ will only work for those libraries. It looks like you are also linking against the boost libraries (likely dynamically) which then link against libgcc and libstdc++.
Try running the following:
ldd mytest
It should show "not a dynamic executable". If it shows anything else, it means it is dynamically linked against other libraries. It doesn't always work so easily, but try adding -static to the compilation line as well to take care of remaining libraries.
I have downloaded and installed the ffmpeg library. I want to use it for reading the separate frames of different videos and manipulate them. For that I tried to follow some tutorial from here: http://dranger.com/ffmpeg/tutorial01.html
But I can't compile my cpp file since I get the following compilation:
Undefined symbols for architecture x86_64:
"av_register_all()", referenced from:
_main in cc9zyUBe.o
_main in ccRz35d4.o
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status
When I was installing ffmpeg library, I used arch=x86_64 option in ./configure step.
I use OS X Mountain Lion 10.8.2 and gcc 4.2 compiler.
Does somebody have any clue what can be the reason of this error?
Thanks in advance.
UPDATE:
I've already tried many different install options, with static libraries, shared libraries, with/without --arch=x86_64 option. Also installed it with homebrew, result remains the same. Library isn't recognized. But ffmpeg binary works pretty well, when I use it as a command-line tool.
Finally I have managed to compile my program which uses ffmpeg library.
For some reason I still couldn't compile it using gcc compiler, but I could do it with g++ compiler.
When the static libraries are installed, all the dependencies must be specified explicitly, and the order of linking of these libraries is also important. So here is the compilation code which finally compiled my program:
g++ readVideo.cc -o readVideo $(pkg-config --libs --cflags libavformat)
pkg-config here is a utility which prints all the flags and libraries that are needed to properly link the specified libavformat library.
Also it's worth of mentioning, that the source file was renamed from readVideo.C to readVideo.cc, and that #include statements have been encompassed using extern "C" as follows:
extern "C" {
#include <libavformat/avformat.h>
}
It is needed because ffmpeg is a C project and program will not compile with C++ compiler if you don't explicitly state that it is C library.
And if you don't want to bother with pkg-config to include all dependencies for ffmpeg libraries, you can install ffmpeg with shared libraries instead of static ones. Then it will compile by simpler call:
g++ readVideo.cc -o readVideo -lavformat
To install shared libraries, you need to add these 2 options to ./configure program when installing ffmpeg:
--disable-static --enable-shared
Hope it helps somebody some time ...
The error means that you aren't linking to the ffmpeg libraries. Simply including the header files is not enough. You need to also link to the actual library files. On Windows they have .lib extension, on Linux usually .a extension, not sure about Mac.
I've installed GCC 3.4 to /opt/gcc-3.4, and I'm using it to compile legacy code which is incompatible with GCC 4. This also means old versions of the C(++) standard libraries, binutils, and utility libraries.
It works fine for some libraries, but fails when compiling libtiff, because it picks up the system libraries in /usr/lib (see output below). This might be an autotools/configure issue, but I'm not sure. I can't find a configure switch or environment variable, and I'd rather not modify my system /usr/lib/libc.so .
So how to make sure it links to the standard library in /opt/gcc-3.4.4/lib, and ignores /lib and /usr/lib completely?
Output of make (excerpt):
libtool: link: g++ -shared -nostdlib /usr/lib/crti.o /opt/gcc-3.4.3/lib/gcc/i686-pc-linux-gnu/3.4.3/crtbeginS.o .libs/tif_stream.o -Wl,--whole-archive ../port/.libs/libport.a -Wl,--no-whole-archive -Wl,-rpath -Wl,/home/jason/d0src34/prereq/tiff-3.9.4/libtiff/.libs -Wl,-rpath -Wl,/opt/gcc-3.4.3/lib -Wl,-rpath -Wl,/home/jason/d0src34/prereq/usr/lib -Wl,-rpath -Wl,/opt/gcc-3.4.3/lib ../libtiff/.libs/libtiff.so -L/usr/lib /usr/lib/libjpeg.so -lz -L/opt/gcc-3.4.3/lib/gcc/i686-pc-linux-gnu/3.4.3 -L/opt/gcc-3.4.3/lib/gcc/i686-pc-linux-gnu/3.4.3/../../.. /opt/gcc-3.4.3/lib/libstdc++.so -L/home/jason/Downloads/gcc-3.4.3/build/i686-pc-linux-gnu/libstdc++-v3/src -L/home/jason/Downloads/gcc-3.4.3/build/i686-pc-linux-gnu/libstdc++-v3/src/.libs -L/home/jason/Downloads/gcc-3.4.3/build/gcc -lm -lc -lgcc_s /opt/gcc-3.4.3/lib/gcc/i686-pc-linux-gnu/3.4.3/crtendS.o /usr/lib/crtn.o -Wl,-soname -Wl,libtiffxx.so.3 -o .libs/libtiffxx.so.3.9.4
/home/jason/d0src34/prereq/usr/bin/ld:/usr/lib/libc.so: file format not recognized; treating as linker script
/home/jason/d0src34/prereq/usr/bin/ld:/usr/lib/libc.so:5: parse error
I've found a (hackish) answer to my own question:
I've been using binutils 2.15, because later versions have an incompatibility with GCC 3.4. In more recent versions, the format of /usr/lib/libc.so has changed, and the old binutils can't parse it.
I temporarily commented out the last line (with "GROUP"), and my code compiled:
/* GNU ld script
Use the shared library, but some functions are only in
the static library, so try that secondarily. */
OUTPUT_FORMAT(elf32-i386)
/* GROUP ( /lib/libc.so.6 /usr/lib/libc_nonshared.a AS_NEEDED ( /lib/ld-linux.so.2 ) ) */
However, I'm not really satisfied, since I can hardly tell other people who want to use the code to edit their system files. Also, I'm not sure if I've linked it to the correct glibc version, since the system /usr/lib is still in the search path, so I can't tell for sure if the binaries will work on other systems.