How to link some .o files in kernel?

speranza · 04-16-2024, 10:25 AM

Hi friends,I have a question.It has been bothering me for a while.Here is details:
I'm adding some ebpf helpers into the kernel.My kernel version is 5.15.153
I modify /kernel/bpf/helpers.c like that:
…
#include "../../security/dir/header.h"
…
BPF_CALL1(func1,argType,argName){
func2(argName);
return 0;
}
…

The function "func2" is in another .c file.That file can't be compiled with kernel because it uses some standard lib such as stdio,stdlib.So I compile it in gcc and get the .o file.I think maybe that .o file can be linked with "helpers.o".But I don't get any idea after I check the Makefile of the kernel and not find any information for this question.

Actually I find two similar question in stackoverflow and here:
https://stackoverflow.com/questions/...-kernel-binary
https://www.linuxquestions.org/quest...kbuild-694396/
But I don't think these can resolve my question.

I want to ask that is it possible to link a .o file with kernel?I think that I need to modify the Makefile in somewhere.

teckk · 04-16-2024, 02:37 PM

https://docs.kernel.org/kbuild/makefiles.html
https://docs.kernel.org/5.10/kbuild/modules.html
https://www.kernel.org/doc/html/v5.1...-syscalls.html

murugesandins · 04-16-2024, 03:01 PM

I do not have your OS here.
I don't have your code here.
Hence I tried simulating your sample code at bash.exe/gcc.exe using CYGWIN_NT at windows.
cat CommonMakefile

Code:

all:
	@echo inside $@;\
	echo call /usr/bin/make ACTION=kernel CompileAtAnyOS;\
	/usr/bin/make ACTION=kernel CompileAtAnyOS
CompileAtAnyOS:
	@echo inside $@;\
	OS=$$(uname -s | sed "s/-[0-9]*\.[0-9]*-[0-9]*//;");\
	echo call /usr/bin/make ACTION=$$ACTION $$OS;\
	/usr/bin/make ACTION=$$ACTION $$OS
CYGWIN_NT:
	@echo inside $@;\
	echo calling /usr/bin/make $(ACTION);\
	CFLAGS=-O3 \
	CC=/usr/bin/g++ \
	cc=/usr/bin/gcc \
	INCLUDE_DIR=../../security/dir \
	/usr/bin/make $(ACTION)
kernel:$(BUILD)
	@echo inside $@

cat Makefile

Code:

BUILD	=	ERP
include CommonMakefile
ERP:
	@if [[ ! -f helpers.o ]];\
	then\
		echo $(cc) -c $(CFLAGS) helpers.c;\
		$(cc) -c $(CFLAGS) helpers.c;\
	else\
		/usr/bin/ls -tr helpers.c \
		helpers.o 2>&1 |\
		/usr/bin/tail -1 |\
		/usr/bin/grep helpers.o >/dev/null 2>&1;\
		Ret=$$?;\
		if [[ 0 -eq $$Ret ]];\
		then\
			echo helpers.o is up to date;\
		else\
			echo $(cc) -c $(CFLAGS) helpers.c -I$(INCLUDE_DIR);\
			$(cc) -c $(CFLAGS) helpers.c -I$(INCLUDE_DIR);\
		fi;\
	fi;\
	if [ ! -f ./a.out ];\
	then\
		echo $(cc)  $(CFLAGS) mymain.c helpers.o  -I$(INCLUDE_DIR) -o ./a.out;\
		$(cc)  $(CFLAGS) mymain.c helpers.o  -I$(INCLUDE_DIR) -o ./a.out;\
	else\
		/usr/bin/ls -tr ./a.out helpers.o mymain.c 2>&1 |\
		/usr/bin/grep a.out >/dev/null 2>&1;\
		Ret=$$?;\
		if [[ 0 -eq $$Ret ]];\
		then\
			echo "./a.out is up to date";\
		else\
			echo $(cc)  $(CFLAGS) mymain.c helpers.o  -I$(INCLUDE_DIR) -o ./a.out;\
			$(cc)  $(CFLAGS) mymain.c helpers.o  -I$(INCLUDE_DIR) -o ./a.out;\
		fi;\
	fi

cat helpers.c

Code:

#include "header.h"
// I am defining macro since I am not sure about actual definition of func1/argType/argName at your code.
#define func1 int arg1
#define argType int arg2
#define argName int arg3
#define BPF_CALL1 void bpf_call1
#define func2(argName) extern void func2(argName)
// I am defining func2 based on same reason
void fun2(int parameter )
{
	return;
}
BPF_CALL1(func1,argType,argName)
{
	func2(argName);
	return;
}

cat mymain.c

Code:

#include <stdio.h>
#include <header.h>
void func2(int arg)
{
	printf( "%d\n", arg);
	return;
}
int main()
{
	func2(12);
}

I created empty header file ..\..\security\dir\header.h

Code:

$ file ../../security/dir/header.h
../../security/dir/header.h: empty

Sample compilation using bash.exe/make.exe at cygwin_nt

Code:

$ /usr/bin/make.exe
inside all
call /usr/bin/make ACTION=kernel CompileAtAnyOS
make[1]: Entering directory '/home/murugesan_openssl'
inside CompileAtAnyOS
call /usr/bin/make ACTION=kernel CYGWIN_NT
make[2]: Entering directory '/home/murugesan_openssl'
inside CYGWIN_NT
calling /usr/bin/make kernel
make[3]: Entering directory '/home/murugesan_openssl'
/usr/bin/gcc -c -O3 helpers.c -I../../security/dir
/usr/bin/gcc -O3 mymain.c helpers.o -I../../security/dir -o ./a.out
inside kernel
make[3]: Leaving directory '/home/murugesan_openssl'
make[2]: Leaving directory '/home/murugesan_openssl'
make[1]: Leaving directory '/home/murugesan_openssl'
$ make
inside all
call /usr/bin/make ACTION=kernel CompileAtAnyOS
make[1]: Entering directory '/home/murugesan_openssl'
inside CompileAtAnyOS
call /usr/bin/make ACTION=kernel CYGWIN_NT
make[2]: Entering directory '/home/murugesan_openssl'
inside CYGWIN_NT
calling /usr/bin/make kernel
make[3]: Entering directory '/home/murugesan_openssl'
helpers.o is up to date
./a.out is up to date
inside kernel
make[3]: Leaving directory '/home/murugesan_openssl'
make[2]: Leaving directory '/home/murugesan_openssl'
make[1]: Leaving directory '/home/murugesan_openssl'
$ /usr/bin/touch.exe helpers.c
$ /usr/bin/make
inside all
call /usr/bin/make ACTION=kernel CompileAtAnyOS
make[1]: Entering directory '/home/murugesan_openssl'
inside CompileAtAnyOS
call /usr/bin/make ACTION=kernel CYGWIN_NT
make[2]: Entering directory '/home/murugesan_openssl'
inside CYGWIN_NT
calling /usr/bin/make kernel
make[3]: Entering directory '/home/murugesan_openssl'
/usr/bin/gcc -c -O3 helpers.c -I../../security/dir
/usr/bin/gcc -O3 mymain.c helpers.o -I../../security/dir -o ./a.out
inside kernel
make[3]: Leaving directory '/home/murugesan_openssl'
make[2]: Leaving directory '/home/murugesan_openssl'
make[1]: Leaving directory '/home/murugesan_openssl'
$ make
inside all
call /usr/bin/make ACTION=kernel CompileAtAnyOS
make[1]: Entering directory '/home/murugesan_openssl'
inside CompileAtAnyOS
call /usr/bin/make ACTION=kernel CYGWIN_NT
make[2]: Entering directory '/home/murugesan_openssl'
inside CYGWIN_NT
calling /usr/bin/make kernel
make[3]: Entering directory '/home/murugesan_openssl'
helpers.o is up to date
./a.out is up to date
inside kernel
make[3]: Leaving directory '/home/murugesan_openssl'
make[2]: Leaving directory '/home/murugesan_openssl'
make[1]: Leaving directory '/home/murugesan_openssl'

murugesandins · 04-16-2024, 03:06 PM

I am feeling much happy after writing above comment

enjoy maadi => enjoy => at kannadaa
nanukku kannada solpha solpha barathu => I knew only few words at kannada(Karnataka Kannada language) even though I am staying there from 2004 to till now.