I want to supply the shared libraries along with my program rather than using the target system's due to version differences.
ldd says my program uses these shared libs:
linux-gate.so.1 => (0xf7ef0000)**(made by kernel)**
libc.so.6 => /lib32/libc.so.6 (0xf7d88000)**(libc-2.7.so)**
/lib/ld-linux.so.2 (0xf7ef1000)**(ld-2.7.so)**
I have successfully linked ld-xxx.so by compiling with:
gcc -std=c99 -D_POSIX_C_SOURCE=200112L -O2 -m32 -s -Wl,-dynamic-linker,ld-2.7.so myprogram.c
But I have not managed to successful link libc-xxx.so. How can I do that ?
I found out how to do it:
rpath specifies where the provided libraries are located. This folder should contain: libc.so.6, libdl.so.2, libgcc_s.so.1 and maybe more. Check with strace to find out which libraries your binary file uses.
ld.so is the provided linker
gcc -Xlinker -rpath=/default/path/to/libraries -Xlinker -I/default/path/to/libraries/ld.so program.c
Passing -nodefaultlibs or -nostdlib to gcc will tell it to not pass the default libraries as arguments to ld. You will then be able to explicitly specify the libc you want to link against. See the gcc(1) man page for more details and caveats regarding both options.
Related
When I run clang/gcc to compile a .c file, I don't need to explicitly link to libc. But it still works as libc and two additional libraries are automatically linked. Why does gcc/clang know to link automatically? Where is this behavior mentioned?
$ cat main.c
/* vim: set noexpandtab tabstop=2: */
#include <stdio.h>
int main() {
puts("Hello World!");
return 0;
}
$ clang -o main.exe main.c # or gcc
$ ./main.exe
Hello World!
$ nm -D /lib/x86_64-linux-gnu/libc-2.27.so | grep -w puts
00000000000809c0 W puts
$ ldd main.exe
linux-vdso.so.1 (0x00007ffe743ba000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f397ce7b000)
/lib64/ld-linux-x86-64.so.2 (0x00007f397d26c000)
Why does gcc/clang know to link automatically?
The GCC developers built this into GCC as a convenience. Which libraries are linked by default is partly affected by the language being compiled, which is deduced from the file names and may be controlled with the -x switch.
Where is this behavior mentioned?
This page in the GCC documentation mentions there are some libraries linked in by default and says you can disable or modify this behavior with -nostdlib and other switches, but I do not see an explicit list of the libraries that are linked in by default. It might vary by system/platform as well as by language. You can use the -v switch to ask GCC to show you the commands it is executing, and the link command (using ld) should reveal the libraries.
I've build a shared library on my desktop that uses statically linked gstreamer and gstreamer plugins (base, good, rtsp-server).
Now I'm trying to compile the library using yocto but its giving me a linker error:
version node not found for symbol _IO_do_write##GLIBC_2.17
failed to set dynamic section sizes: Bad value
The solutions I found on stack overflow did not seem to help me.
use compiler with --disable-symvers
link libc libs in different orders (-ldl -lm -lc -lpthread -ltinfo -lrt)
link libc libs statically/shared
What I find particularly odd is that the linker is looking for GLIBC_2.17 while yocto uses 2.27 and my system is using 2.24. I don't know if this matters or if it is normal (the function did not change since 2.17?).
NM -C shows the symbol in libc.a:
nm -C recipe-sysroot/usr/lib/libc.a | grep IO_do_write
U _IO_do_write
U _IO_do_write
0000000000001ba8 W _IO_do_write
So I would thinks that lib is linked incorrectly?
The linker command is a long one because of all the shared libs so I shortend it a bit (removed boost and custom libs):
aarch64-poky-linux-g++ -fPIC --sysroot=recipe-sysroot -O2 -pipe -g -feliminate-unused-debug-types -fdebug-prefix-map=recipe-root/git-r0 -fdebug-prefix-map=recipe-sysroot= -fdebug-prefix-map=recipe-sysroot-native= -fvisibility-inlines-hidden --sysroot=recipe-sysroot -Wl,-allow-multiple-definition -Wall -Wextra -Wpedantic -Wsuggest-override -Wswitch-default -Wduplicated-cond -Wshadow -Werror -ftemplate-depth=1024 -Wl,-O1 -Wl,--hash-style=gnu -Wl,--as-needed -lc -Wl,--no-as-needed -Wl,--no-undefined -pthread -ldl -shared -Wl,-soname,rtsp_streamer.so -o rtsp_streamer.so ... custom static libs .and boost static libs ... -lpthread recipe-sysroot/usr/lib/gstreamer-1.0/libgstrtsp.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstrtp.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstrtpmanager.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstcoreelements.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstadder.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstapp.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstaudioconvert.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstaudiorate.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstaudioresample.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstaudiotestsrc.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstgio.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstpango.a recipe-sysroot/usr/lib/gstreamer-1.0/libgsttypefindfunctions.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstvideoconvert.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstvideorate.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstvideoscale.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstvideotestsrc.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstvolume.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstautodetect.a recipe-sysroot/usr/lib/gstreamer-1.0/libgstvideofilter.a recipe-sysroot/usr/lib/libBrokenLocale.a recipe-sysroot/usr/lib/libBrokenLocale_pic.a recipe-sysroot/usr/lib/libanl.a recipe-sysroot/usr/lib/libanl_pic.a recipe-sysroot/usr/lib/libatomic.a recipe-sysroot/usr/lib/libatomic_ops.a recipe-sysroot/usr/lib/libatomic_ops_gpl.a ... more boost static libs ... recipe-sysroot/usr/lib/libc.a recipe-sysroot/usr/lib/libc_nonshared.a recipe-sysroot/usr/lib/libc_pic.a recipe-sysroot/usr/lib/libcidn_pic.a recipe-sysroot/usr/lib/libcrypt.a recipe-sysroot/usr/lib/libcrypt_pic.a recipe-sysroot/usr/lib/libcrypto.a recipe-sysroot/usr/lib/libdl.a recipe-sysroot/usr/lib/libdl_pic.a recipe-sysroot/usr/lib/libg.a recipe-sysroot/usr/lib/libgomp.a recipe-sysroot/usr/lib/libgstallocators-1.0.a recipe-sysroot/usr/lib/libgstaudio-1.0.a recipe-sysroot/usr/lib/libgstbase-1.0.a recipe-sysroot/usr/lib/libgstcheck-1.0.a recipe-sysroot/usr/lib/libgstcontroller-1.0.a recipe-sysroot/usr/lib/libgstfft-1.0.a recipe-sysroot/usr/lib/libgstpbutils-1.0.a recipe-sysroot/usr/lib/libgstreamer-1.0.a recipe-sysroot/usr/lib/libgstriff-1.0.a recipe-sysroot/usr/lib/libgstrtp-1.0.a recipe-sysroot/usr/lib/libgstrtsp-1.0.a recipe-sysroot/usr/lib/libgstrtspserver-1.0.a recipe-sysroot/usr/lib/libgstapp-1.0.a recipe-sysroot/usr/lib/libgstnet-1.0.a recipe-sysroot/usr/lib/libgstsdp-1.0.a recipe-sysroot/usr/lib/libgsttag-1.0.a recipe-sysroot/usr/lib/libgstvideo-1.0.a recipe-sysroot/usr/lib/libhistory.a recipe-sysroot/usr/lib/libitm.a recipe-sysroot/usr/lib/liblicensing.a recipe-sysroot/usr/lib/libm.a recipe-sysroot/usr/lib/libm_pic.a recipe-sysroot/usr/lib/libmcheck.a recipe-sysroot/usr/lib/libncurses++.a recipe-sysroot/usr/lib/libncurses++w.a recipe-sysroot/usr/lib/libnsl.a recipe-sysroot/usr/lib/libnsl_pic.a recipe-sysroot/usr/lib/libnss_compat_pic.a recipe-sysroot/usr/lib/libnss_db_pic.a recipe-sysroot/usr/lib/libnss_dns_pic.a recipe-sysroot/usr/lib/libnss_files_pic.a recipe-sysroot/usr/lib/libnss_hesiod_pic.a recipe-sysroot/usr/lib/libnss_nis_pic.a recipe-sysroot/usr/lib/libnss_nisplus_pic.a recipe-sysroot/usr/lib/libprotobuf-lite.a recipe-sysroot/usr/lib/libprotobuf.a recipe-sysroot/usr/lib/libprotoc.a recipe-sysroot/usr/lib/libpthread.a recipe-sysroot/usr/lib/libpthread_nonshared.a recipe-sysroot/usr/lib/libreadline.a recipe-sysroot/usr/lib/libresolv.a recipe-sysroot/usr/lib/libresolv_pic.a recipe-sysroot/usr/lib/librpcsvc.a recipe-sysroot/usr/lib/librt.a recipe-sysroot/usr/lib/librt_pic.a recipe-sysroot/usr/lib/libsqlite3.a recipe-sysroot/usr/lib/libssl.a recipe-sysroot/usr/lib/libssp.a recipe-sysroot/usr/lib/libssp_nonshared.a recipe-sysroot/usr/lib/libstdc++.a recipe-sysroot/usr/lib/libstdc++fs.a recipe-sysroot/usr/lib/libsupc++.a recipe-sysroot/usr/lib/libthread_db_pic.a recipe-sysroot/usr/lib/libutil.a recipe-sysroot/usr/lib/libutil_pic.a recipe-sysroot/usr/lib/libz.a recipe-sysroot/usr/lib/librt.a recipe-sysroot/usr/lib/libpthread.a recipe-sysroot/usr/lib/libm.a recipe-sysroot/usr/lib/libc.a
Does anybody know what is wrong? If more info is needed please ask. Thanks in advance!
Does anybody know what is wrong?
I suspect that you are not linking against GLIBC-2.27 from Yocto, but against some other GLIBC, though it is hard to see how that could happen.
Your first step should be to find out which libc.so.6 is actually being used. You can do so by adding -Wl,-t flag to your link line. Also add -Wl,-y,_IO_do_write while you are at it.
After you know which libc.so.6 is being used, run readelf -Ws /path/to/libc.so.6 | grep _IO_do_write to see what (if any) versioned symbols are defined in it.
I don't know if this matters or if it is normal (the function did not change since 2.17)?
Yes: that is normal -- the function didn't change its ABI since GLIBC-2.17, so that's the version that is attached to it.
I figured out what went wrong. The shared library is build using a CMAKE project and our own written FindGSTREAMER.cmake. To find gstreamer, among other things, a glob is used to find all the static libs. Because on my desktop I have gstreamer installed in its seperate location this works. With Yocto however this causes every static lib in the recipe-sysroot/usr/lib directory to be linked. Including every libc library (.a, _pic.a and .so). Apparently this causes the linker unable to resolve the symbols.
Correctly filtering the libraries needed by gstreamer fixed the problem.
I am cross compiling for a system with an OpenMP parallelized program, but when I run on the target, I get the error:
can't load library 'libgomp.so.1'
After looking around, I see that it's an OpenMP runtime library. Is there any was to statically link the library it on the compiler host machine, or does it need to be present on the target machine? If it can be statically linked, then what makes a runtime library different from a dynamic library? Could one statically or dynamically link any library, provided the environment was correct?
You can selectively statically link certain libraries by providing certain linker options. For libgomp it would be something like:
gcc -o executable foo.o bar.o -Wl,-static -lgomp -Wl,-Bdynamic -lpthread -lother -llibs
Any library listed between -Wl,-static and -Wl,-Bdynamic will be linked in statically. -fopenmp should not be present in the linking command as it expands to linker flags that get appended after the user supplied options, and therefore libpthread should be listed explicitly. It also means that even simple OpenMP programs have to be compiled and linked in two separate steps for static linking to work.
Example:
// foo.c
#include <stdio.h>
#include <omp.h>
int main(void)
{
#pragma omp parallel
printf("Hello world from thread %d\n", omp_get_thread_num());
return 0;
}
Traditional compilation:
$ gcc -fopenmp -o foo foo.c
$ ldd foo
linux-vdso.so.1 => (0x00007ffff5661000)
libgomp.so.1 => /usr/lib64/libgomp.so.1 (0x0000003bcfa00000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x0000003bc2600000)
libc.so.6 => /lib64/libc.so.6 (0x0000003bc1e00000)
librt.so.1 => /lib64/librt.so.1 (0x0000003bc3200000)
/lib64/ld-linux-x86-64.so.2 (0x0000003bc1a00000)
The program is linked against the DSO version of libgomp.
Fully static linking:
$ gcc -fopenmp -static -o foo foo.c
$ ldd foo
not a dynamic executable
With -static all libraries are linked in statically into the executable.
Linking only libgomp statically:
$ gcc -fopenmp -c foo.c
$ gcc -o foo foo.o -Wl,-static -lgomp -Wl,-Bdynamic -lpthread
$ ldd foo
linux-vdso.so.1 => (0x00007ffdaaf61000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x0000003bc2600000)
libc.so.6 => /lib64/libc.so.6 (0x0000003bc1e00000)
/lib64/ld-linux-x86-64.so.2 (0x0000003bc1a00000)
It is important to maintain the correct order of statically linked objects in that case. If foo.o is placed after -lgomp, a link error results:
$ gcc -o foo -Wl,-static -lgomp -Wl,-Bdynamic foo.o -lpthread
foo.o: In function `main':
foo.c:(.text+0x14): undefined reference to `GOMP_parallel_start'
foo.c:(.text+0x23): undefined reference to `GOMP_parallel_end'
foo.o: In function `main.omp_fn.0':
foo.c:(.text+0x3b): undefined reference to `omp_get_thread_num'
collect2: ld returned 1 exit status
Any object file resulting from source code that contains OpenMP constructs should be placed before -lgomp.
The term "runtime library" is usually used for the standard library and environment needed to run your program. In the case of a C program, it's the C standard library, maybe some other libraries specific for your compiler, and some object files linked to your program to set up the standard C environment.
A "runtime library" can be a dynamic library, or even a collection of multiple dynamic libraries. But it can also be one or more static libraries as well.
Dynamic libraries are convenient way of providing runtime libraries, as many programs will potentially want to link against such a library. And this is why dynamic linking and dynamic libraries are out there - the first process that requires particular dynamic library will cause it to be loaded to memory. Later, this instance of dynamic library can be reused by many processes.
Imagine if you'd have tens of process running and each of them statically link against say C runtime library. I assume memory consumption would grow rather significantly compared to the case where each of these processes would link against single DLL.
In my opinion, if library will be used by many different processes (for example DirectX might be such library) it might be more efficient to provide it as dynamic library. Otherwise, static linking is preferable.
I'm trying to use Scons to build a simple project on a server on which I have rights to install stuff only in specific locations (and not in /usr/ ). Since I'm not happy with default compiler the server is offering me, I installed g++4.8 and verified it works just fine. But when I try to use Scons to build a simple project, while it picks up correct g++ (I can get that by checking the version), it's looking for libstdc++ in /usr/ directories instead of the directory where g++4.8 installation resides. E.g. code compiles, but upon execution fails with:
./main: /usr/lib64/libstdc++.so.6: version `GLIBCXX_3.4.9' not found (required by ./main)
Again - this doesn't happen when I call the compiler myself from the terminal.
Even when I add the lib path containing libraries for g++4.8 with LIBPATH option, I get the same error.
Here's my SConscript file:
Import('env')
COMPILER_FLAGS = '-Wall -fopenmp -O3 -std=c++11'
LINK_FLAGS = '-Wall -fopenmp -O3 -std=c++11'
LIB_PATH = 'myfolder/gcc-4.8.2/lib64'
PROGRAM = 'main'
SRC = ['main.cpp', 'Foo.cpp']
env.Append(CPPFLAGS = COMPILER_FLAGS)
env.Append(LINKFLAGS = LINK_FLAGS)
env.Program(target = PROGRAM, source = SRC, LIBPATH = LIB_PATH)
and SConstruct is just
import os
env = Environment(ENV = os.environ)
SConscript('./SConscript', exports=['env'], duplicate=0)
Edit:
I made sure location of my compiler comes in the path before default compiler. But even if I set it explicitly with Environment(CXX=...) it's the same story. Here's the build output:
/mypath/gcc-4.8.2/bin/g++ -o Foo.o -c -Wall -fopenmp -O3 -std=c++11 Foo.cpp
/mypath/gcc-4.8.2/bin/g++ -o main.o -c -Wall -fopenmp -O3 -std=c++11 main.cpp
/mypath/gcc-4.8.2/bin/g++ -o main -Wall -fopenmp -O3 -std=c++11 main.o Foo.o -L/mypath/gcc-4.8.2/lib64
scons: done building targets.
-bash-3.2$
-bash-3.2$
-bash-3.2$ ./main
./main: /usr/lib64/libstdc++.so.6: version `GLIBCXX_3.4.9' not found (required by ./main)
./main: /usr/lib64/libstdc++.so.6: version `GLIBCXX_3.4.11' not found (required by ./main)
-bash-3.2$
Yet another edit:
ldd on both manual and scons compile reveal:
linux-vdso.so.1 => (0x00007fff513fd000)
libstdc++.so.6 => /usr/lib64/libstdc++.so.6(0x0000003e7f600000)
libm.so.6 => /lib64/libm.so.6 (0x0000003e79600000)
libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x0000003e7de00000)
libc.so.6 => /lib64/libc.so.6 (0x0000003e79200000)
/lib64/ld-linux-x86-64.so.2 (0x0000003e78e00000)
So indeed even manual compile doesn't look for the libs in the right directory (or where I installed the compiler) and the problem isn't with the scons itself, but likely that I didn't configure something right, but then I'm really puzzled as to why the executable runs fine, while it doesn't for scons.
Ok, so my problem wasn't with scons, but with me not giving explicit paths to nonstandard locations of libstdc++ and friends. SO answer over here explains this in more detail:
Linking g++ 4.8 to libstdc++
You're misinterpreting the error. GCC always knows how to find its own libraries, including libstdc++. The problem is that after you've compiled the program the runtime linker (which is not part of GCC, it's part of your OS and comes from glibc) doesn't know how to find the newer libstdc++, so it finds the default system one, which is too old.
The problem and solution are described at in the Libstdc++ FAQ, "How do I insure that the dynamically linked library will be found?", and manual, "Finding Dynamic or Shared Libraries"
This doesn't sound right.
Can you show us what you do to override the compiler?
If you are only doing the above, I don't think your compiler will be overridden with the new version.
You need to do something like
env = Environment(CC='/path/to/gcc')
Or Environment(CXX='/path/to/g++') if you want to override the c++ compiler
Or is your path on your environment setup to have the directory of the custom compiler before the standard compilers directory?
It might help to clean and then run with scons with --debug=presub which will show you the command line used to build each target.
Also your environment is a dictionary, so try printing out different keys to make sure they match what you expect:
print env['CC']
print env['CXX']
In Linux, I have a shared library I made that uses pthreads and a main.c that does not.
libpthread.so shows up in an ldd of my shared library, which is correct.
$ ldd libmapreduce.so.1.0
linux-gate.so.1 => (0x0067d000)
libpthread.so.0 => /lib/libpthread.so.0 (0x0058c000)
[...]
But when I compile and link my main.c that does not use pthreads to my shared library that does, I see:
$ icc -Wall -o main main.c -lmapreduce
/opt/intel/Compiler/11.1/046/lib/ia32/libiomp5.so: undefined reference to `pthread_atfork'
Adding -lpthread to my compile command, i.e.,
$ icc -Wall -o main main.c -lmapreduce -lpthread
resolves the undefined reference.
Why do I need to explicitly link to libpthread when my main.c does not use it and my shared library already has libpthread linked in?
In order to create an executable or DLL you need to link in the transitive closure of all dependencies in your program. Because main.c links in sharedlib you must also link in all dependencies of sharedlib which includes pthreads.
Thank you R.. and Pavan Manjunath, for encouraging me to keep digging.
The link step for the shared library libmapreduce.so looked like:
icc -shared -g -o libmapreduce.so.1.0 map.o map_wrp.o -openmp [...] -lpthread -ldl
That -openmp link flag was not needed and in fact introduced the undefined reference to pthread_atfork. The undefined reference to pthread_atfork did not show up until I tried to link a main.c with the shared library libmapreduce.so. Re-creating libmapreduce.so without the -openmp flag removed the problem.