How to dynamically link libraries in automake? - linux

I'm trying to build a package on lauchpad. For it to build I need to set a static path using the LDADD variable in automake:
relay_LDADD = /usr/lib/x86_64-linux-gnu/libm.so /usr/lib/x86_64-linux-gnu/libX11.so.6 $(RELAY_LIBS)
This compiles on the 64 bit build but fails on the 32 bit build. I tried using PKG_CHECK_MODULES but it says
No package 'm' found
No package 'X11' found
Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.
I know it not a non standard path since launchpad is doing the building? How can I get this to work?
The build failed without the libraries specified even though the package specifies them in the build-requires.

You have tried to outwit the buid-system, and it has outwitted you.
It's generally a bad idea to hard-code paths.
Debian (and ubuntu is just a derivative), has started to ship binaries (like libraries) in architecture-dependent directories, to allow installations for multiple architectures on a single system.
These libraries are installed into /usr/lib/<host-triplet>, where <host-triplet> depends on the architecture; e.g. x86_64-linux-gnu is the amd64 architecture for systems with a linux and the gnu tools.
a 32bit system would typically have a host-triplet of i386-linux-gnu.
Since you are hard-coding the library path to a 64bit location( /usr/lib/x86_64-linux-gnu/libm.so) this fails on all systems but 64bit/linux/gnu.
Instead you should just tell the linker to link against the m library (libm), resp the X11 library (libX11).
Let the linker care for the correct architecture to pick:
relay_LDADD = -lm -lX11 $(RELAY_LIBS)
In general, if you want to link against a library foo, that provides a library-file libfoo.so you would use -lfoo (stripping away the leading lib and the trailing .so).
However, sometimes this is not enough; in those cases your library might use pkg-config to provide the full CFLAGS and LDFLAGS needed to compile/link against this library.
e.g. if I want to use libquicktime:
$ pkg-config --cflags libquicktime
-I/usr/include/lqt
$ pkg-config --libs libquicktime
-lquicktime -lpthread -lm -lz -ldl
So I would use something like:
myprog_CFLAGS += $(shell pkg-config --cflags libquicktime)
myprog_LDADD += $(shell pkg-config --libs libquicktime)
That would work in any GNU(?) Makefile (not related to autotools).
In an autotools project, you would probably move the pkg-config check into configure, using the m4-macro PKG_CHECK_MODULES

Related

Override/clear g++ default search path for libraries

Question
I want to override/clear g++ default search path for libraries, so that g++ does only search libraries under paths explicitly specified:
$ arm-linux-gnueabihf-g++ --print-search-dirs | grep libraries:
libraries: =/usr/lib/gcc-cross/arm-linux-gnueabihf/6/:/usr/lib/gcc-cross/arm-lin
ux-gnueabihf/6/../../../../arm-linux-gnueabihf/lib/arm-linux-gnueabihf/6/:/usr/l
ib/gcc-cross/arm-linux-gnueabihf/6/../../../../arm-linux-gnueabihf/lib/arm-linux
-gnueabihf/:/usr/lib/gcc-cross/arm-linux-gnueabihf/6/../../../../arm-linux-gnuea
bihf/lib/../lib/:/lib/arm-linux-gnueabihf/6/:/lib/arm-linux-gnueabihf/:/lib/../l
ib/:/usr/lib/arm-linux-gnueabihf/6/:/usr/lib/arm-linux-gnueabihf/:/usr/lib/../li
b/:/usr/lib/gcc-cross/arm-linux-gnueabihf/6/../../../../arm-linux-gnueabihf/lib/
:/lib/:/usr/lib/
Can this be done?
Background
I'm on Ubuntu 17.04 compiling c++ code for several cross-platform distributions.
I've installed Ubuntu g++-arm-linux-gnueabihf package, and created a target image under /opt/jessie_root, in this case for Jessie armhf. I also fixed all the links under this jessie_root image to be relative and not absolute.
I want to compile dynamic executables with the target rootfs libraries.
Initially I was compiling "fine" but I realized that I was linking to symbols on the host cross-toolchain libstdc++.
I'm using cmake, but for simplicity consider this commands:
/usr/bin/arm-linux-gnueabihf-g++ main.c
This will link to the host libstdc++ under /usr/lib/gcc-cross/arm-linux-gnueabihf/6/libstdc++.so, which is not desirable.
/usr/bin/arm-linux-gnueabihf-g++ main.cpp --sysroot=/opt/jessie_root -L=/usr/lib/gcc/arm-linux-gnueabihf/4.9 -D_GLIBCXX_USE_CXX11_ABI=0
This will link correctly to the target libstdc++ under /opt/jessie_root/usr/lib/gcc/arm-linux-gnueabihf/4.9/libstdc++.so, which I want.
The issue is that this seems a disaster waiting to happen, as if one of the default libs are not found on the target, the compiler will haply take one from the host cross-toolchain.
I could remove or rename them, but I don't want to mess on /usr/.
I have also played with GCC -nostdlib and LD -nostdlib, which seem to have different meanings. GCC -nostdlib is for libraries, and LD -nostdlib is for the search directories. LD -nostdlib have no effect, and GCC -nostdlib just forces me to specify the libraries manually, but it still keeps the search paths.
Naturally I could use another toolchain/compile my own, but I would prefer to stay on the packaged toolchain.

How do I link libraries from multiple locations (corresponding to multiple GCC versions)?

I am currently trying to use Oracle Linux 6 OS on a SPARC S7 server to run the NPB benchmarks (with OpenMP multithreading support). The OS comes preloaded with gcc 4.4.7, which is missing the Niagara 7 optimizations. I downloaded devtoolset-3 from the Oracle Yum Repository, which has gcc 4.9.2 installed in /opt/rh/devtoolset-3/root/usr/bin. However, when I compile the NPB benchmark using the newer gcc, it automatically links to libraries associated with the older gcc 4.4.7 (located in /usr/lib). This caused my program to segfault during execution. I believe that it is because libgomp 4.4.7 is incompatible with libgomp 4.9.2. I have tried several ways of linking to the libraries in the gcc 4.9.2 folder (which is /opt/rh/devtoolset-3/root/usr/lib/gcc); none of the methods work:
-Xlinker -rpath=lib_location
-Wl -Bstatic
-L lib_location
The closest I got was when using -Wl -Bstatic ~/libgomp.a or -static -L ~/libgomp.a. It fails to find libraries such as libm that reside in the default gcc lib folder (usr/lib).
The actual command used to link is:
/opt/rh/devtoolset-3/root/usr/bin/gcc -O3 -fopenmp -mcmodel=medmid -static -L/opt/rh/devtoolset-3/root/usr/lib/gcc/sparc64-redhat-linux/4.9.2 -o ../bin/bt.W.x bt.o initialize.o exact_solution.o exact_rhs.o set_constants.o adi.o rhs.o x_solve.o y_solve.o solve_subs.o z_solve.o add.o error.o verify.o ../common/print_results.o ../common/c_timers.o ../common/wtime.o -lm -L/opt/rh/devtoolset-3/root/usr/lib/gcc/sparc64-redhat-linux/4.9.2/lib/
/opt/rh/devtoolset-3/root/usr/libexec/gcc/sparc64-redhat-linux/4.9.2/ld: cannot find -lm
/opt/rh/devtoolset-3/root/usr/libexec/gcc/sparc64-redhat-linux/4.9.2/ld: cannot find -lrt
/opt/rh/devtoolset-3/root/usr/libexec/gcc/sparc64-redhat-linux/4.9.2/ld: cannot find -lpthread
/opt/rh/devtoolset-3/root/usr/libexec/gcc/sparc64-redhat-linux/4.9.2/ld: cannot find -lc
Is there a way I can link just the libgomp library from gcc 4.9.2 while linking the remaining libraries from gcc 4.4.7?
The devtoolset compilers are all using the system libgcc, libstdc++, version 4.4.7, and can therefore not compile e.g. c++11.
I guess the gcc53-c++-5.3.0-1.el6.x86_64.rpm will do. Comes with the internal */gcc53/lib64{libgcc_s.so**, libgomp.so**, libstdc++} (version 5.3.0) ... Provides /usr/bin/{ gcc53, g++53 }
The package was created a year ago ... well tested, as extra compiler. Download link : https://drive.google.com/file/d/0B7S255p3kFXNbTBneHgwSzBodFE/view?usp=sharing
If you're going to do the -Wl,-Bstatic thing, make sure to follow it immediately by -Wl,-Bdynamic to reset to normal after your added library argument. By default, not all system libraries have static versions installed, which is why you get e.g. cannot find -lc.
So you can try this as a modification of your workaround:
-Wl,-Bstatic ~/libgomp.a -Wl,-Bdynamic
Not pretty, and this question deserves a much better answer (this is still pretty much a hack), but it should get the job done for now.

Link against which libraries for GTK functions?

may be this is a stupid question but I don't find a solution for my own. For a very simple application I use a few functions gdk_window_reparent() and gtk_widget_get_window().
But: against what library do I need to link in order to resolve these dependencies?
-lgtk
does not do the trick, the name must be something different...
Thanks!
You use a program called pkg-config to generate the compiler and linker flags you need to build GTK+ software.
pkg-config --cflags gtk+-3.0 # compiler flags only
pkg-config --libs gtk+-3.0 # linker flags only
pkg-config --cflags --libs gtk+-3.0 # both
If you are building from a shell or a makefile, you can use backticks to capture the output from these programs and add them to the current command line. If you are using a build system, see how it integrates with pkg-config.

Preparing GNU toolchain for bare metal ARM on Linux

I would like to prepare GNU toolchain for bare metal ARM to use it with Geany IDE. There are some tutorials like this one: Building the GNU ARM Toolchain for Bare Metal but I do not understand few steps.
First of all, everyone who uses Linux OS implicitly has gcc, binutils and gdb so why to download others? Secondly all tutorials tell me to configure gcc with something like that: *./configure --target=arm-elf. What does it even do ? Does it just force me to call gcc in command line using arm-elf-gcc instead of gcc or does it change some internal options of my gcc ?
So far I have prepared makefile but I am still not sure about compiler options. I have not changed any gcc configure options and I call compiler with such flags:
CFLAGS = -Wall -std=c99 -march=armv7-m -mtune=cortex-m0
Can I prepare toolchain just with calling gcc with proper arguments or do I need to make some changes in gcc configuration ?
GCC and its target
GCC is always configured to emit binaries for a specific target. So normally the gcc which is already available on Linux has the target "i486-linux-gnu". You can't cross-compile to an ARM target using this compiler.
So you need to install another GCC configured for that target; then GCC and the other programs normally have a prefix indicating the target: In your case the prefix is arm-none-eabi, and then you call that GCC using arm-none-eabi-gcc. You can have multiple GCC installations, they do not interact (if they interact, you have probably screwed up something - always install in separate directories, if you do it manually).
Installing
If your Linux distribution provides a package, you could just install that one (on Debian this is "gcc-arm-none-eabi").
You can download a pre-compiled package: GNU Tools for ARM Embedded Processors.
You can try to compile one. Not really easy, if you want correct multi-libs.
If your Linux distribution provides a package > 4.8.0, you should try that one.
If you want to have multiple versions installed (and be able to switch between them easily), the second option is possibly better. I stopped compiling a GCC for ARM when the second option was available.
Cross-compiling
In your Makefile you have to make sure that the cross-compiler is used. You could use $(CC) in your Makefile, and assign it like this:
TOOLCHAIN = arm-none-eabi-
CC = $(TOOLCHAIN)gcc
Compiler flags for Cortex-M0 are -mcpu=cortex-m0 -mthumb -mfloat-abi=soft which is by convention assigned to CFLAGS
CFLAGS += -mcpu=cortex-m0 -mthumb -mfloat-abi=soft
Then a (simple) rule to compile .c to .o looks like
%.o: %.c
$(CC) $(CFLAGS) -o $# -c $<
Tutorials which use the arm-elf- prefix are out-dated. Currently arm-none-eabi- is in use.

configure test with static lib

I am trying to cross compile libpng for RaspberryPi on Ubuntu 14.04 (x_64) with zlib
but configure fails with
configure:11400: arm-linux-gnueabihf-gcc -o conftest -g -O2 -I/home/user/RPI_DEV/lib/include conftest.c -lz -lm >&5
/home/user/RPI_DEV/xtools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/../lib/gcc/arm-linux-gnueabihf/4.8.3/../../../../arm-linux-gnueabihf/bin/ld: cannot find -lz
collect2: error: ld returned 1 exit status
configure:11400: $? = 1
configure: failed program was:
....
Because I am using toolchain for arm, arm-ld cant find zlib.
Is there any option for configure not to compile with shared lib but to try with static lib (eg. -static -lz).
Command is
./configure --enable-static=true --enable-shared=false --with-zlib-include="/home/user/RPI_DEV/lib/include" --with-zlib-lib="/home/user/RPI_DEV/lib/lib" LDFLGS="-L/home/user/RPI_DEV/lib/lib" CPPFLAGS="-I/home/user/RPI_DEV/lib/include" -enable-static --host=arm-linux-gnueabihf --prefix=/home/user/RPI_DEV/lib --exec-prefix=/home/user/RPI_DEV/lib
You need to cross build and install zlib into your toolchain before trying to use it in another project.
What you are doing might work but only if you spell LDFLAGS correctly:
LDFLGS="-L/home/user/RPI_DEV/lib/lib"
Note the missing 'A'. I don't know why your second attempt worked, given you had the same misspelling; possibly you had a correct LDFLAGS in your environment?
Anyway there should be a Ubuntu cross-development guide somewhere that explains how to do this. It's slightly off topic but for Gentoo you use 'crossdev' to install the toolchain then a crossdev specific version of the normal package installation mechanism ([host]-emerge) to install zlib into the toolchain.
Also, the arguments --with-zlib-include and --with-zlib-lib are not supported by any current version of libpng I can find. If you are cross-compiling libpng for an RPi (or, indeed, any ARM system) you should be using the latest version of 1.6 that you can find.
Unless someone solves this the RIGHT way, this is hack I've done.
Open configure.ac file
Find and comment out line
AC_CHECK_LIB(z, zlibVersion, , AC_ERROR([zlib not installed]))
Configure will pass wihout check for zlib and then add zlib by hand
LDFLGS="-L/home/user/RPI_DEV/lib/lib -L/home/user/RPI_DEV/lib/lib/libz.a"
Run autoconf
Run ./configure ...

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