I compiled with gcc
gcc -l. 'net-snmp-config --cflags'
-fPlC -shared -c -o matsu_object.o tsu_object.c
but this error occurred
gcc: -lcrypto: Because a link was
not completed, the input file of the
linker was not used
What's wrong?
Did you mistype the question? There's no way for that to output the message you write, and I would expect that the proper command is something more like
gcc -L. `net-snmp-config --cflags` -fPIC -shared -c -o matsu_object.o tsu_object.c
Notice the -L uppercase, backticks instead of single quotes, and upper-case I in PIC.
Also, you don't say what you're trying to do, but net-snmp-config should also take at least one of --libs or --agent-libs as well.
Ah, I didn't read closely enough...
-c means "compile", that is: generate from tsu_object.c, a compiled matsu_object.o.
Without -c, the compiler actually links, that is: generate from *.o, a.out or other specified file.
-shared (and linker flags like -l and -L) are only meaningful when linking. They're meaningless when compiling, as you are doing here because of -c.
Please correct the command-line in the question to accurately reflect what you're running, and give some more explanation as to what you're trying to do.
I think you are using ticks ' instead of back ticks `. Does --cflags really give linker options? I think you are at the link step here. Also what is the effect of -c at a link. I thought -c was compile only and not attempt to link.
You used single quotes instead of backquotes.
Instead of this:
gcc -l. 'net-snmp-config --cflags' -fPlC -shared -c -o matsu_object.o tsu_object.c
You should type:
gcc -l. `net-snmp-config --cflags`-fPlC -shared -c -o matsu_object.o tsu_object.c
net-snmp-config is a program. When you run it with --cflags, it evaluates to the correct cflags that you should be using to compile your program.
But you know what? You should be using autoconf. Even for something this small, it usually makes sense to do the work. Most people I know need to compile on more than one platform...
Related
How to create a makefile for Linux for the next command?
gcc -shared -home/ time.c /libperi.a -o time.so
First, pick a name. This command appears to build time.so, so that's a good name.
The makefile is just a text file. Write it like this:
time.so:
gcc -shared -home/ time.c /libperi.a -o time.so
That whitespace before the gcc is a TAB, not spaces.
Once you have that working, you can read the manual and learn more about Make, which will allow you to write more powerful rules.
Here I am compiling a C code with the following Makefile.
MAIN:
g++ -c -o td.o -I/home/user/dp/pro/include td.c
g++ -c -o disk.o -I/home/user/dp/pro/include disk.c
g++ -o disk disk.o tds2.o -L ${DP_LIB} -L ${LIPN_LIB} -lgnb -lgtd -lnbl -lpin
./disk.exe RUN.dat
What is the purpose of -L ${DP_LIB} here? Precisely, I wish to know the function of ${}.
If it is linking a library, how is it different from -llib?
This makefile is by far very crude (I have seen bigger and better ones). I am new to makefiles, but atleast this one works.
The -L options is telling the linker to add a path to the list it uses to search for libraries. The ${DP_LIB} thing is how variables are used in makefiles. Presumably DP_LIB is a path to somewhere.
All this should be very clear if you just read the documentation and the actual makefile.
With -Ldir you specify a directory where the linker searches for libs. The lib files themselves are specified with the -llib argument.
Example:
-L/usr/X11R6/lib -lX11
means that the linker will look for libX11.so in /usr/X11R6/lib
(...and in other default places.)
I need help it is bug or I don't understand how compilation options are working ?
I have sample main.c file and try to compile it as:
$ g++ -nostdlib -g -fno-rtti -fno-exceptions -ffreestanding -nostdinc -nostdinc++ -Wl,--build-id=none,-g,-nostdlib,-nostartfiles,-zmax-page-size=0x1000 main.c -o main
and as output I have this:
$ ls
main.c startfiles
I am trying to understand why g++ created file named "startfiles" not "main" ?
If you read the GNU ld official documentation you will see that there is no option named -nostartfiles. What you do pass for arguments to the linker with that is the options -n and -ostartfiles.
If I were you, I would check those other options you try to pass to the linker as well.
-nostartfiles is a compiler flag as far as I know, not a linker flag.
For the linker, it's the same as -n -o startfiles, which is why you're getting that output file name.
In a particular project, I saw the following compiler options used all at once:
gcc foo.c -o foo.o -Icomponent1/subcomponent1 -Icomponent2/subcomponent1 -Wall -fPIC -s
Are the -fPIC and -s used together contradictory here? If not, why?
-s and -fPIC are two flags used for different purposes. They are not contradictory.
From the gcc manual
-s
Remove all symbol table and relocation information from the executable.
-fPIC
If supported for the target machine, emit position-independent code, suitable for dynamic linking and avoiding any limit on the size of the global offset table. This option makes a difference on the m68k, PowerPC and SPARC.
I use a custom build tool to compile go projects and I need a way to use cgo in my project.
The problem is that the cgo documentation only tells you how to use it with make.
What I really need to know is which generated files to process with which tools and in what order it needs to be done. I tried to read make.pkg in the go source dir but my best effort fails.
My test dll is very simple, a single function that returns 1 every time it is called and the go code to use this function is similarly simple.
The output from the console produced by a successful run of make on a cgo project would be very helpful.
Output of running make on 32-bit Linux in directory misc/cgo/life:
# gomake _obj/life.a
CGOPKGPATH= cgo -- life.go
touch _obj/_cgo_run
8g -o _go_.8 _obj/life.cgo1.go _obj/_cgo_gotypes.go
8c -FVw -I ${GOROOT}/pkg/linux_386 -I . -o "_cgo_defun.8" _obj/_cgo_defun.c
gcc -m32 -I . -g -fPIC -O2 -o _cgo_main.o -c _obj/_cgo_main.c
gcc -m32 -g -fPIC -O2 -o c-life.o -c c-life.c
gcc -m32 -I . -g -fPIC -O2 -o life.cgo2.o -c _obj/life.cgo2.c
gcc -m32 -I . -g -fPIC -O2 -o _cgo_export.o -c _obj/_cgo_export.c
gcc -m32 -g -fPIC -O2 -o _cgo1_.o _cgo_main.o c-life.o life.cgo2.o _cgo_export.o
cgo -dynimport _cgo1_.o >_obj/_cgo_import.c_ && mv -f _obj/_cgo_import.c_ _obj/_cgo_import.c
8c -FVw -I . -o "_cgo_import.8" _obj/_cgo_import.c
rm -f _obj/life.a
gopack grc _obj/life.a _go_.8 _cgo_defun.8 _cgo_import.8 c-life.o life.cgo2.o _cgo_export.o
The line cgo -- life.go creates the following files:
_obj/_cgo_.o
_obj/life.cgo1.go
_obj/life.cgo2.c
_obj/_cgo_gotypes.go
_obj/_cgo_defun.c
_obj/_cgo_main.c
_obj/_cgo_flags
_obj/_cgo_export.c
_cgo_export.h
"I use a custom build tool to compile go projects and I need a way to use cgo in my project."
... and this approach leads to problems. Using the standard way with a Makefile is simple, easy, proven, documented, etc.
I realize I'm not (directly) answering your question. Instead my "answer" is: I strongly suggest to use the standard way. Don't create problems for your self by choosing other, not directly supported options.
That said, I think there is a way to avoid the Makefiles, I just never been there, sorry. I'm usually lazy/short of time, so I use the simplest/fastest way to get things done. You might want to try the same ;-)