I use the following LLVM tools to convert a cpp project which is written in multiple files into "ONE" single assembly file.
clang *.cpp -S -emit-llvm
llvm-link *.s -S -o all.s
llc all.s -march=mips
Is there any way of doing this in GCC? In particular, is there any way of linking GCC generated assembly files into one assembly file? i.e., what is the equivalent of LLVM-LINK?
Perhaps LTO (Link Time Optimization) is what you want.
Then, compile each compilation unit with gcc -flto e.g.
gcc -flto -O -Wall -c src1.c
g++ -flto -O -Wall -c src2.cc
and use also -flto (and the same optimizations) to link them:
g++ -flto -O src1.o src2.o -lsomething
LTO works in GCC by putting, in each generated assembly file and object file, some representation of the internal GCC representations (like Gimple). See its documentation
You might want to use MELT to customize GCC (or simply use its probe to understand the Gimple, or try just gcc -fdump-tree-all).
Related
I am trying to better understand link-time optimization in GCC and -fuse-linker-plugin seems to matter in that context. However, I do not exactly understand how.
Suppose my compilation with link-time optimization looks like this:
gcc a.c -c -o a.o -flto -fno-fat-lto-objects
gcc b.c -c -o b.o -flto -fno-fat-lto-objects
gcc main.c -o main.out a.o b.o
What would be a good use case for enabling -fuse-linker-plugin?
I found the official GCC documentation somewhat confusing on that point. They suggest that -fuse-linker-plugin matters only for archive files (.a) but most conversation I have seen mentions that option without discussing archive files.
I'm trying to link multiple .o files using gfortran. I've compiled the files like so (in a makefile):
gfortran -c -fopenmp file1.f
gfortran -c -fopenmp file2.f
Now I'd like to link the files with an option for OpenMP. I know with the Intel compiler the linking flag is -liomp5, so to link the files with the Intel compiler one would call:
ifort -o a.out file1.o file2.o -liomp5
This is obviously not the correct flag for the GNU compiler. What is the correct OpenMP linking flag for gfortran?
It is -fopenmp as well:
gfortran -fopenmp -o a.out file1.o file2.o
I compile with the following command:
gcc -Wall -march=native -O3 -ffast-math -I/usr/local/include -I/usr/local/include -o waon main.o notes.o midi.o analyse.o fft.o hc.o snd.o -L/usr/local/lib -L/usr/local/lib -lfftw3 -L/usr/local/lib -lsndfile -lm
I now would like to compile with Emscripten. How do I convert the above gcc command into an emcc command?
The command you have described in the question is linking rather than compiling. However in general you should just be able to replace gcc with emcc and it will do the right thing. In this case you will need to replace not only this linking command but also the commands used to compile the sources to the .o files.
It would probably be a good idea to take out the -march option.
It looks like your project is using libsndfile and FFTW. You will probably need to compile these libraries yourself using emscripten. Both of them are using autotools so with a bit of luck you can compile them with emscripten simply by adding the following parameters when you run the configure script:
./configure --prefix=$HOME/emscripten-libs CC=emcc
make && make install
Then when you link your program you can specify -L$HOME/emscripten-libs/lib instead of -L/usr/local/lib.
Make research about emsdk download&setup on your computer.
Download emsdk instruction
Next interest link is :
emcc or em++ instruction
https://emscripten.org/docs/tools_reference/emcc.html
When you setup emcc in command line you can see this project (i make emcc final look based on python script runner.py etc.):
c-cpp-to-javascript
Basic and useful example's :
Pretty analog with gcc :
Args:
-lGL for openGL
-s TOTAL_MEMORY=512MB --memory-init-file 1 Memory staff
--preload-file folderWithImages/--use-preload-plugins If you use assets
-I forInclude/someheader.h
-L libraryFolder/someLib.lib
-std=c11
Simple run:
./emcc -O2 a.cpp -o a.js
or
./emcc -O2 a.cpp -o a.html
Links:
./emcc -O2 a.cpp -o a.bc
./emcc -O2 b.cpp -o b.bc
./emcc -O2 a.bc b.bc -o project.js
Or :
to get JS
emcc -s WASM=1 myAdds.a myLib.a source1.c source2.cpp -o build.js
to get html
emcc -s WASM=1 myAdds.a myLib.a source1.c source2.cpp -o build.html
Link together the bitcode files:
emcc project.bc libstuff.bc -o allproject.bc
Compile the combined bitcode to HTML
emcc allproject.bc -o final.html
Important note :
You can't take an existing .a library and convert it. You must build lib with emcc also.
i have a makefile for some code library i'm using and now i've added to that code some code that uses gsl. i'm not so sure how and what to add to the makefile (which i wat to keep since it's invoking boost as well) that would invoke gsl.
This is my makefile:
CXX = g++
ARCH = -mtune=generic
# ARCH = -march=core2
# ARCH = -march=native
COFLAGS = $(ARCH) -O3 -pipe
CXXFLAGS = -Wall $(COFLAGS)
PROGRAMS = getData analyzeData
BOOSTFLAGS = -I .
OPENMP = -fopenmp -DSUPPORT_OPENMP
all: $(PROGRAMS)
getData: getData.cpp common.o parse.o common.h
$(CXX) $(CXXFLAGS) getData.cpp common.o parse.o -o getData
analyzeData: analyzeData.cpp common.o parse.o parameters.o
$(CXX) $(CXXFLAGS) $(BOOSTFLAGS) $(OPENMP) estimateCrossReplicatesExpression.cpp common.o parse.o parameters.o -o analyzeData
parameters.o: parameters.cpp parameters.h
parse.o: parse.cpp parse.h
common.o: common.cpp common.h
clean:
rm *.o $(PROGRAMS)
In case GSL is installed on the default path (/usr/local/include/gsl) on your system, the compilation command for a source file "example.c" would be
gcc -Wall -I/usr/local/include -c example.c
The library is installed as a single file, libgsl.a. A shared version of the library libgsl.so is also installed on systems that support shared libraries. The default location of these files is /usr/local/lib. If this directory is not on the standard search path of your linker you will also need to provide its location as a command line flag.
To link against the library you need to specify both the main library and a supporting cblas library, which provides standard basic linear algebra subroutines. A suitable cblas implementation is provided in the library libgslcblas.a if your system does not provide one. The following example shows how to link an application with the library,
$ gcc -L/usr/local/lib example.o -lgsl -lgslcblas -lm
The option -lm links with the system math library. On some systems it is not needed.
Thus, you need to specify the gsl specific flags in your compile command. Update the Makefile accordingly.
I was trying to do something like this in a makefile:
program.exe: ui.o main.o
gcc ......etc
ui.o: window1.o window2.o
gcc -c window1.o window2.o -o ui.o #this doesn't want to work
window1.o: window1.c window1.h window1_events.c window1_controls.c ...
gcc -c window1.c window1_events.c window1_controls.c... -o window1.o
window2.o: ...
gcc ...
main.o: ...
gcc ...
but when I compile like this, it gives the error "input file unused because linking not done," and then I get a bunch of unresolved externs, etc--problems which are resolved by changing
program.exe: ui.o main.o
gcc ...
to
program.exe: window1.o window2.o main.o
gcc ...
so is it possible to just link object files together, to avoid having mile-long lines in a makefile and break down the build process a little more?
Yes: to merge several object files into one, use ld -r or ld -Ur:
From "man ld" on Linux:
-r
--relocatable
Generate relocatable output---i.e., generate an output file that can
in turn serve as input to ld. This is often called partial linking.
As a side effect, in environments that support standard Unix magic
numbers, this option also sets the output file’s magic number to
"OMAGIC".
If this option is not specified, an absolute file is produced.
When linking C++ programs, this option will not resolve references to
constructors; to do that, use -Ur.
You could also do this with gcc:
gcc -Wl,-r foo.o bar.o -o foobar.o -nostdlib
Merging object files like this has some advantages over using an archive library: if merged files change very infrequently (compared to say main.c), your final executable links will be faster.
OTOH, with archived library, the linker will only use what it needs, so your executable may end up being smaller if e.g. window2.c ends up not being necessary.
I bunch of object files is a library. You can create a library with the ar
utility. The following example creates a library called mylib.a containing the files foo.o and bar.o
ar rvs mylib.a foo.o bar.o
You can then link with it by using it on the compiler command line:
gcc -o myexe main.c mylib.a
To create a library:
ar rvs somelib.a file1.o file2.o file3.o
To link it:
gcc -o program.exe file4.o somelib.a