I'm trying to make a relocatable object file with gcc. I use solution from this post. The solution works fine with ld:
$ ld -r a.o b.o -o c.o
However when I try to use it with gcc, the following error happens:
$ gcc -r a.o b.o -o c.o
/usr/bin/ld: cannot find -lgcc_s
/usr/bin/ld: cannot find -lgcc_s
collect2: ld returned 1 exit status
Using the -Wl,-r and -Wl,--relocatable options gives the same result.
Is there any way to link relocatable object file with gcc or I'm forced to use ld for doing this?
To solve this problem, the -nostdlib option must also be passed to gcc:
$ gcc -r -nostdlib a.o b.o -o c.o
I don't know it for sure, but it seems without this option gcc tries to link standard libraries into output relocatable object.
Related
I'm trying to get my head around how the linking process works when producing an executable. To do that I'm reading Ian Taylor's blog series about it, but a lot of it is beyond me at the moment - so I'd like to see how it works in practice.
At the moment I produce some object files and link them via gcc with:
gcc -m32 -o test.o -c test.c
gcc -m32 -o main.o -c main.c
gcc -m32 -o test main.o test.o
How do I replicate the gcc -m32 -o test main.o test.o stage using ld?
I've tried a very naive: ld -A i386 ./test.o ./main.o
But that returns me these errors:
ld: i386 architecture of input file `./test.o' is incompatible with i386:x86-64 output
ld: i386 architecture of input file `./main.o' is incompatible with i386:x86-64 output
ld: warning: cannot find entry symbol _start; defaulting to 00000000004000b0
./test.o: In function `print_hello':
test.c:(.text+0xd): undefined reference to `_GLOBAL_OFFSET_TABLE_'
test.c:(.text+0x1e): undefined reference to `puts'
./main.o: In function `main':
main.c:(.text+0x15): undefined reference to `_GLOBAL_OFFSET_TABLE_
I'm most confused by _start and _GLOBAL_OFFSET_TABLE_ being missing - what additional info does gcc give to ld to add them?
Here are the files:
main.c
#include "test.h"
void main()
{
print_hello();
}
test.h
void print_hello();
test.c
#include <stdio.h>
void print_hello()
{
puts("Hello, world");
}
#sam : I am not the best people to answer your question because I am a beginner in compilation. I know how to compile programs but I do not really understand all the details (https://en.wikipedia.org/wiki/Compilers:_Principles,_Techniques,_and_Tools)
So, I decided this year to try to understand how compilation works and I tried to do, more or less, the same things as you tried a few days ago. As nobody has answered, I am going to expose what I have done but I hope an expert will supplement my answer.
Short answer : It is recommended to not use ld directly but to use gcc directly instead. Nevertheless, it is, as you write, interesting to know how the linking process works. This command works on my computer :
ld -m elf_i386 -dynamic-linker /lib/ld-linux.so.2 -o test test.o main.o /usr/lib/crt1.o /usr/lib/libc.so /usr/lib/crti.o /usr/lib/crtn.o
Very Long answer :
How did I find the command above ?
As n.m suggested, run gcc with -v option.
gcc -v -m32 -o test main.o test.o
... /usr/libexec/gcc/x86_64-redhat-linux/4.8.5/collect2 ... (many
options and parameters)....
If you run ld with these options and parameters (copy and paste), it should work.
Try your command with -m elf_i386 (cf. collect2 parameters)
ld -m elf_i386 test.o main.o
ld: warning: cannot find entry symbol _start; ....
Look for symbol _start in object files used in the full ld command.
readelf -s /usr/lib/crt1.o (or objdump -t)
Symbol table '.symtab' contains 18 entries: Num: Value Size
Type Bind Vis Ndx Name... 11: 00000000 0 FUNC
GLOBAL DEFAULT 2 _start
Add this object to your ld command :ld -m elf_i386 test.o main.o /usr/lib/crt1.o
... undefined reference to `__libc_csu_fini'...
Look for this new reference in object files. It is not so obvious to know which library/object files are used because of -L, -l options and some .so include other libraries. For example, cat /usr/lib/libc.so. But, ld with --trace option helps. Try this commandld --trace ... (collect2 parameters)At the end, you should findld -m elf_i386 -o test test.o main.o /usr/lib/crt1.o /usr/lib/libc_nonshared.a /lib/libc.so.6 /usr/lib/crti.oor shorter (cf. cat /usr/lib/libc.so) ld -m elf_i386 -o test test.o main.o /usr/lib/crt1.o /usr/lib/libc.so /usr/lib/crti.o
It compiles but it does not run (Try to run ./test). It needs the right -dynamic-linker option because it is a dynamically linked ELF executable. (cf collect2 parameters to find it) ld -m elf_i386 -dynamic-linker /lib/ld-linux.so.2 -o test test.o main.o /usr/lib/crt1.o /usr/lib/libc.so /usr/lib/crti.o But, it does not run (Segmentation fault (core dumped)) because you need the epilogue of the _init and _fini functions (https://gcc.gnu.org/onlinedocs/gccint/Initialization.html). Add the ctrn.o object. ld -m elf_i386 -dynamic-linker /lib/ld-linux.so.2 -o test test.o main.o /usr/lib/crt1.o /usr/lib/libc.so /usr/lib/crti.o /usr/lib/crtn.o./test
Hello, world
I am trying to do something basic, but I can't find the relevant information on how to compile. I tried the following without success:
gfortran testintegral.f90 -lgsl -lgslcblas
testintegral.f90:19.6:
use fgsl
1
Fatal Error: Can't open module file 'fgsl.mod' for reading at (1): No such file
The file is taken from http://de.wikibooks.org/wiki/Fortran:_FGSL#Beispiel:_Numerische_Integration (page in german but readily understandable) so I suppose it is OK.
Maybe the syntax of the compilation command is incorrect ?
EDIT:
I edit my initial post so as not to bury important information in the comments.
Those are the paths of the libraries:
sudo find -name '*libgsl.so*'
./usr/lib/libgsl.so.0
./usr/lib/libgsl.so.0.17.0
sudo find -name '*libgslcblas.so*'
./usr/lib/libgslcblas.so.0
./usr/lib/libgslcblas.so.0.0.0
But I still got an error message when doing:
gfortran testintegral.f90 -L/usr/lib -I/usr/include/fgsl -lfgsl -lgsl -lgslcblas
/usr/bin/ld: cannot find -lgsl
/usr/bin/ld: cannot find -lgslcblas
collect2: error: ld returned 1 exit status
Use the -I flag. For example,
gfortran -I/usr/local/fgsl/include testintegral.f90 -lgsl -lgslcblas
All the .mod files in that directory are then included.
EDIT: See also comments below.
Compilation of a file containing modules in gfortran produces two file types: The source file foo.f90 is translated into foo.o. If foo.f90 contains the modules bar and baz, then bar.mod and baz.mod are also generated. They contain the interface information for these modules. Note that there is no required mapping between module and file names (although programming guildelines may require this).
When the statement use fsgl is found, the interface information is read from fsgl.mod. If that file is not found, you get the error message
Can't open module file 'fgsl.mod' for reading at (1): No such file
So, you have to change your order of compilation (possibly through changing a Makefile).
1) the easiest way is
gfortran testintegral.f90 -I/usr/local/include/fgsl -lfgsl
2) this also works
gfortran -I/usr/local/include/fgsl testintegral.f90 -lgsl -lgslcblas -lm
3) I read the log of the make check in the package, the developer used such a way
gfortran -I/usr/local/include/fgsl -g -O2 -c -o test.o testintegral.f90
/bin/bash /path/.../fgsl-1.3.0/libtool --tag=FC --mode=link gfortran -g -O2 -o test test.o /usr/local/lib/libfgsl.la -lgsl -lgslcblas -lm
UPDATE:
First check the linkers for fgsl
pkg-config --libs fgsl
probably will get something like this
-L/usr/local/lib -lfgsl -lgsl -lgslcblas -lm
Then you put the linkers, works for all the cases!
gfortran -I/usr/include/fgsl example.f90 -lfgsl -lgsl -lgslcblas -lm
UPDATE: I answered too soon, here is the best universal method I found:
gfortran `pkg-config --cflags fgsl` testintegral.f90 -o integral `pkg-config --libs fgsl`
I'm trying to combine object files created from C++ files into an executable using gcc. Unfortunately, gcc is giving me thousands of undefined reference errors to strings, arrays, etc.
I am doing this on a Windows machine, so no terminal commands; only cmd commands.
I'm simply doing:
gcc a.o b.o c.o -o prgm.exe
What am I missing/doing wrong?
EDIT:
I recreated the .o files with g++ doing:
g++ a.cpp -g -c -Wall -std=c++0x -lSDLmain -lSDL -lSDL_image -lSDL_ttf -IC:\SDL-1.2.14\include -o a.o, where a.cpp and a.o are the directories where i keep the files, not the g++ directory
Then, I did g++ a.o b.o c.o -o prgm.exe. This gave dozens (I guess that's an improvement?) errors like
undefined reference to `_SDL_SetColorKey'
but I included SDL didnt I?
The final error from this is:
c:/program files (x86)/codeblocks/mingw/bin/../lib/gcc/mingw32/4.7.0/../../../li
bmingw32.a(main.o):main.c:(.text.startup+0xa7): undefined reference to `_WinMain
#16'
collect2.exe: error: ld returned 1 exit status
int main(int argc, char * argv[]) is in the code
You are trying to link a C++ program with the C linker. You need to use g++ instead of gcc.
Generally speaking gcc is for compiling/linking C, while g++ is for C++. IIRC compiling C++-code with gcc works by virtue of dispatching according to the file extension. Linking C++ code with gcc however does not work, since it won't link the C++ standard libraries, resulting in your undefined reference errors.
If this does not solve your problem, you might want to give us a more concrete description of your errors and your system.
Based upon your updates then I think you'd need to do the following:
g++ a.cpp b.cpp c.cpp -g -Wall -IC:\SDL-1.2.14\include -LC:\SDL-1.2.14\lib -std=c++0x -lSDLmain -lSDL -lSDL_image -lSDL_ttf -o prgm.exe
I'm guessing C:\SDL-1.2.14\lib exists based upon where the headers are located.
GCC is the C compiler. Your code is C++ so you need to use G++ to do the linking:
g++ a.o b.o c.o -o prgm.exe
This automatically adds the C++ libraries to the link line, resolving many if not all of your missing references.
I'm trying to create a shared library with my gcc. It's a gcc for vxworks (thats probably the problem...).
I use the gcc as following:
./gcc -shared -B/path/to/gnutools/bin -o test.so test.c
Result:
/path/to/ld: -r and -shared may not be used together
collect2: ld returned 1 exit status
If I try the same with the linux gcc, there's no problem. So i guess the gcc for VxWorks automatically passes the -r (or -i, which is the same and results in the same) flag to the linker. Is there a way to suppress this?
Greetz
marty
PS: making it static is not really an alternative...
Try compile object file separately with -fPIC and then link:
gcc -Wall -fPIC -c -o test.o test.c
gcc -Wall -shared -o test.so test.o
Another suggestion is to use libtool (at least to figure out the correct flags).
A workaround may be to go directly with ld:
ld -shared -o test.so test.o -lc
I'm trying to compile a program using a third party library, Omnet++ in my case. Apparently "make" does not find a library, but the path it uses is correct as you can see (in the sense that I can see the library under omnet++ source tree)
pv135168:basic Bob$ opp_makemake
Creating Makefile in /Users/Bob/Code/network_sim/basic... Makefile created, running "make depend" to add dependencies... opp_makedep -Y --objdirtree -I. -f Makefile -P\$O/ -- ./*.cc
pv135168:basic Bob$ make
g++ -c -g -Wall
-fno-stack-protector -m32 -DHAVE_PCAP -DXMLPARSER=libxml
-DWITH_PARSIM -DWITH_NETBUILDER -I.
-I/Users/Bob/Code/omnetpp-4.1/include -o out/gcc-debug//txc1.o txc1.cc g++ -m32 -Wl,-rpath,/Users/Bob/Code/omnetpp-4.1/lib -Wl,-rpath,. -o out/gcc-debug//basic out/gcc-debug//txc1.o -Wl,-all_load
-L"/Users/Bob/Code/omnetpp-4.1/lib/gcc"
-L"/Users/Bob/Code/omnetpp-4.1/lib" -u _tkenv_lib -lopptkenvd
-loppenvird -lopplayoutd -u _cmdenv_lib -loppcmdenvd -loppenvird
-loppsimd -lstdc++
ld: library not found for -lopptkenvd
collect2: ld returned 1 exit status make: *** [out/gcc-debug//basic]
Error 1 pv135168:basic Bob$
It's looking in the following directories for a file called libopptkenvd.dylib or libopptkenvd.a:
/Users/Bob/Code/omnetpp-4.1/lib/gcc
/Users/Bob/Code/omnetpp-4.1/lib
Is that file in one of those directories (or in the standard directories like /usr/lib)? I don't see an indication of that in your output.