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pjp
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Joined: 16 Apr 2002
Posts: 20484
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 Posted: Wed Sep 11, 2024 6:02 pm Post subject: [solved] warning: linker input unused |
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I'm trying to learn how to use Makefiles with linking an external library as well as creating objects, executables and the C "extern" feature. This is sort of a "minimal" example of doing that.
Everything seems to work, although the linker warning doesn't help me understand what the warning means, or what to correct to stop the warning. | Code: | $ make
/usr/lib/llvm/18/bin/clang -Wall -Wextra -std=c11 -pedantic -ggdb -c common.c -lsodium -o obj/common.o
clang: warning: -lsodium: 'linker' input unused [-Wunused-command-line-argument]
/usr/lib/llvm/18/bin/clang -Wall -Wextra -std=c11 -pedantic -ggdb -c foo.c -lsodium -o obj/foo.o
clang: warning: -lsodium: 'linker' input unused [-Wunused-command-line-argument]
/usr/lib/llvm/18/bin/clang -Wall -Wextra -std=c11 -pedantic -ggdb -o foo obj/common.o obj/foo.o -lsodium
$ ./foo
Random number: 8 |
If I remove -lsodium from the Makefile, it produces this error: | Code: | | undefined reference to `randombytes_uniform' |
What should I be doing instead? | Code: | $ cat Makefile
CC=/usr/lib/llvm/18/bin/clang
STANDARD=c11
CFLAGS= -Wall -Wextra -std=$(STANDARD) -pedantic -ggdb
LIBS= -lsodium
SRC=foo.c
SOURCES=$(wildcard ./*.c)
OBJECTS=$(patsubst ./%.c, obj/%.o, $(SOURCES))
EXECUTABLE=foo
all: $(EXECUTABLE)
$(EXECUTABLE): $(OBJECTS)
$(CC) $(CFLAGS) -o $@ $(OBJECTS) $(LIBS)
$(OBJECTS): obj/%.o : ./%.c
$(CC) $(CFLAGS) -c $< $(LIB_PATH) $(LIBS) -o $@ |
| Code: | $ head -15 common.c
#include <sodium.h>
#include <stdbool.h>
unsigned int get_random_number(int max)
{
if (sodium_init() < 0) {
/* Unable to initialize sodium (unsafe, to use) */
return 1;
}
// randombytes_uniform() returns a value: 0 to upper bound (excluded).
int number = (randombytes_uniform(max) + 1);
return number;
}
// Not shown or used (yet) are functions for is_... odd, even. true, false
$ cat foo.c
#include <stdio.h>
#include "foo.h"
int main(void)
{
printf("Random number: %d\n", get_random_number(10));
}
$ cat foo.h
extern int get_random_number(int number); |
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Last edited by pjp on Wed Sep 11, 2024 6:59 pm; edited 1 time in total |
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GDH-gentoo
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Joined: 20 Jul 2019
Posts: 1685
Location: South America
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| Posted: Wed Sep 11, 2024 6:19 pm Post subject: |
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LIBS is only needed in the linking phase, i. e. the recipe for $(EXECUTABLE).
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| NeddySeagoon wrote: | I'm not a witch, I'm a retired electronics engineer  |
| Ionen wrote: | | As a packager I just don't want things to get messier with weird build systems and multiple toolchains requirements though |
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pjp
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Joined: 16 Apr 2002
Posts: 20484
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| Posted: Wed Sep 11, 2024 6:57 pm Post subject: |
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Thanks. | Code: | $ make
/usr/lib/llvm/18/bin/clang -Wall -Wextra -std=c11 -pedantic -ggdb -c common.c -o obj/common.o
/usr/lib/llvm/18/bin/clang -Wall -Wextra -std=c11 -pedantic -ggdb -c foo.c -o obj/foo.o
/usr/lib/llvm/18/bin/clang -Wall -Wextra -std=c11 -pedantic -ggdb -o foo obj/common.o obj/foo.o -lsodium |
As far as the (now deleted) comment about make figuring out how to create object files, that's not something I understand at all. It's a Franken-Makefile I've cobbled together here and there as I've tried to figure out how to do something.
This stuff is a precursor to using multiple directories for source files and how to get them to work together. I tried using src/*.c, that worked. I then added src/sub-dir/*.c, and that didn't work. Next I tried src/*.c and other-src/*.c and couldn't get the two to work.
So for now I'm back with everything in src/*.c
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GDH-gentoo
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Joined: 20 Jul 2019
Posts: 1685
Location: South America
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| Posted: Wed Sep 11, 2024 8:11 pm Post subject: |
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| pjp wrote: | | As far as the (now deleted) comment about make figuring out how to create object files, that's not something I understand at all. |
I saw that you wanted the object files in an obj/ subdirectory, so I deleted the comment.
If you don't mind C source files, object files and the executable in the same directory as the makefile, you can omit the rule for $(OBJECTS), because GNU Make can deduce that it can make common.o and foo.o from their source files by invoking a C compiler, and will use your specified CC and CFLAGS for that. It is using an implicit rule; see the relevant section in info make. That makes the makefile shorter.
If you don't mind object files and the executable in the same directory as the makefile, but have all C source files somewhere else, you can also omit that rule, and add VPATH=/pathname/of/sources/directory (it can be relative to the makefile's directory), so that the source files are searched there in addition to the makefile's directory.
Other variants require a more complicated makefile.
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| NeddySeagoon wrote: | | I'm not a witch, I'm a retired electronics engineer |
| Ionen wrote: | | As a packager I just don't want things to get messier with weird build systems and multiple toolchains requirements though |
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