C: undefined reference to inline function

Question

Since my last question was closed because of bad code style and typo, I reviewed it and ask for help again.

I'm trying to resolve a .exe file with PE format. Here is part of my code

    #include "PE_resolve.h"
    #define SIZEOF_SECTION_HEADER 0x28

     /*load filebuffer into Imagebuffer*/
    int Read_2_ImageBuffer(void **p_filebuffer, void **p_Imagebuffer,long filesize);
    
    /*helper function*/
    inline void * Get_NT_POS(void **p_filebuffer);
    inline void * Get_FileHeader_POS(void **p_filebuffer);
    inline void * Get_Opt_FileHeader_POS(void **p_filebuffer);

    
    int main(){
        return 0;
    }

    int Read_2_ImageBuffer(void **p_filebuffer, void **p_Imagebuffer,long filesize){
       /*allocate memory for imagebuffer*/
       void *Opt_PE_Header = Get_Opt_FileHeader_POS(p_filebuffer); //THE ERROR LINE
       DWORD SizeOfImage = *(DWORD*) ((BYTE *)Opt_PE_Header + 0x38);
       *p_Imagebuffer = malloc(SizeOfImage);
        if(*p_Imagebuffer == NULL){
            printf("can't allocate enough heap memory\n");
            exit(EXIT_FAILURE);
        }
        memset(*p_Imagebuffer,0,SizeOfImage);
    
       /*.....something deal the memory.....*/
       return 0;
    }

    inline void * Get_NT_POS(void **p_filebuffer){
        /*return void * point to NT_header in filebuffer*/
        DWORD offset = *(DWORD*)((BYTE *)*p_filebuffer + 0x3c);
        return (BYTE *)*p_filebuffer + offset;
    }

    inline void * Get_FileHeader_POS(void **p_filebuffer){
         /*return void * point to PE_header in filebuffer*/
         void *nt_pos = Get_NT_POS(p_filebuffer);
         return (BYTE *)nt_pos + sizeof(DWORD);
    }
 
    inline void * Get_Opt_FileHeader_POS(void **p_filebuffer){
        /*return void * point to option_PE_header in filebuffer*/
        void *fileheader_pos = Get_FileHeader_POS(p_filebuffer);
        return (BYTE *)fileheader_pos + 0x14; 
    }

And this is PE_resolve.h

#ifndef __PE_resolve_header
#define __PE_resolve_header
#define IMAGE_SIZEOF_SHORT_NAME 8

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef char BYTE; 
typedef short WORD;
typedef int DWORD;

typedef struct _IMAGE_SECTION_HEADER {
    BYTE Name[IMAGE_SIZEOF_SHORT_NAME];
    union {
        DWORD PhysicalAddress;
        DWORD VirtualSize;
    } Misc;
    DWORD VirtualAddress;
    DWORD SizeOfRawData;
    DWORD PointerToRawData;
    DWORD PointerToRelocations;
    DWORD PointerToLinenumbers;
    WORD NumberOfRelocations;
    WORD NumberOfLinenumbers;
    DWORD Characteristics;
} _IMAGE_SECTION_HEADER;

#endif

when I compile it with MinGW, it follows with undefined reference to `Get_Opt_FileHeader_POS'

C:\MinGW\bin\gcc.exe -g D:\Compile\PE_resolve\PE_loader.c -o D:\Compile\PE_resolve\PE_loader.exe
c:/mingw/bin/../lib/gcc/mingw32/8.2.0/../../../../mingw32/bin/ld.exe: C:\Users\15205\AppData\Local\Temp\ccadB6tt.o: in function `Read_2_ImageBuffer':
D:/Compile/PE_resolve/PE_loader.c:52: undefined reference to `Get_Opt_FileHeader_POS'

As you see, I implement all functions in this .c file with prototype at the beginning. I'm a little frustrated. Could you please tell me the reason that cause the ERROR ? Thx :(

Answer 1

You can add the static keyword before every inline function.
By doing that you force the linker to include the function symbol in the symbol table:

static inline void *Get_Opt_FileHeader_POS(void **p_filebuffer);

Another option is to simply remove the inline keyword.