Embed text in C code

drew77 · September 13, 2018, 2:37pm

I hope c coding is ok here.

I am fairly new at c coding.

I simply want to embed some text in the executable.

I tried this but can't find the text using Ghex.

#include <stdio.h>
const char * S = "andrew";

int main()
{
printf("Hello World!\n");
return 0;
}

milhan · September 13, 2018, 4:05pm

#include <stdio.h>

const char *str = "andrew";

int main()
{
  printf("Hello World! %s\n", str);
  return 0;
}

Corona688 · September 13, 2018, 6:48pm

drew77:

I simply want to embed some text in the executable.

I tried this but can't find the text using Ghex.
#include <stdio.h>
const char * S = "andrew";

int main()
{
printf("Hello World!\n");
return 0;
}

Text strings won't be embedded in the code, they will reside in the data segment.

drew77 · September 13, 2018, 7:08pm

Ok.

Can I get it embedded in the code segment where it will be near the top when viewed with a hex editor?

Corona688 · September 17, 2018, 6:08pm

Tricky. Most large-scale architectures separate data and code.

What you might be able to find is the value of the pointer.

#include <stdio.h>

int main(void)
{
        printf("%p\n", "fixed text");
}

Compile and run that and you'll be given a hexadecimal value. Search for that value in the code segment and you won't find the text itself, but you'll find something which uses it.

Marck · October 27, 2018, 2:32am

Embedding a text file in C code. Therefore it might be easier if you just load the text from a file at runtime, or embed the text directly into the code.

int main()
{
    const char* text = "
#include "file.txt"
";
    printf("%s", text);
    return 0;

drew77 · October 27, 2018, 3:22pm

Embedded_Text.c:3:17: warning: unused variable �text� [-Wunused-variable]
     const char* text = "

Corona688 · October 28, 2018, 1:33pm

The C language, the C preprocessor, and the linker do not work that way.

Besides, altering what you stuff into a pair of double quotes doesn't move it into the code segment. It will be in the data segment, just like before, when he couldn't find it.

To stuff non-code content into the code segment, assembly language might be required.

wisecracker · October 28, 2018, 5:46pm

You could try inline assembler inside your C code using a simple short jump to a NOP and filling the gap with define bytes with the hex values of the string you want to display:
Pseudo-code...

Enter the C _asm_ extension statement inside the beginning of _main_.

        jmp short LABEL:
        db        0x??
        db        0x??
        .
        .
        db        0x??
LABEL:
        nop

Close assembler statement and continue.

This will safely give 120 characters worth of define byte[s], 'db'.
Where ?? are the hex values of the characters.
It might work under gcc...
I have no idea if this would work under gcc, (it does work on C compilers on other older platforms).

------ Post updated at 09:46 PM ------

This might attach itself to the previous code:

#include <stdio.h>

int main(void)
{
    /* This should be inside this assembler code. */
    asm ("jmp getout;"
         "useless: .asciz \"Barry Walker!\n\";"
         "getout:;"
         "nop;"
    );
    printf("This should be in the data section.\n");
    printf("Testing the hidden string.\n");
    return 0;
}

Results OSX 10.13.6, default bash terminal compiled under gcc.

Last login: Sun Oct 28 21:37:54 on ttys000
AMIGA:amiga~> cd Desktop/Code/C
AMIGA:amiga~/Desktop/Code/C> gcc embed.c
AMIGA:amiga~/Desktop/Code/C> ./a.out
This should be in the data section.
Testing the hidden string.
AMIGA:amiga~/Desktop/Code/C> hexdump -C a.out
00000000  cf fa ed fe 07 00 00 01  03 00 00 80 02 00 00 00  |................|
00000010  0f 00 00 00 b0 04 00 00  85 00 20 00 00 00 00 00  |.......... .....|
00000020  19 00 00 00 48 00 00 00  5f 5f 50 41 47 45 5a 45  |....H...__PAGEZE|
00000030  52 4f 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |RO..............|
00000040  00 00 00 00 01 00 00 00  00 00 00 00 00 00 00 00  |................|
00000050  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000060  00 00 00 00 00 00 00 00  19 00 00 00 d8 01 00 00  |................|
00000070  5f 5f 54 45 58 54 00 00  00 00 00 00 00 00 00 00  |__TEXT..........|
00000080  00 00 00 00 01 00 00 00  00 10 00 00 00 00 00 00  |................|
00000090  00 00 00 00 00 00 00 00  00 10 00 00 00 00 00 00  |................|
000000a0  07 00 00 00 05 00 00 00  05 00 00 00 00 00 00 00  |................|
000000b0  5f 5f 74 65 78 74 00 00  00 00 00 00 00 00 00 00  |__text..........|
000000c0  5f 5f 54 45 58 54 00 00  00 00 00 00 00 00 00 00  |__TEXT..........|
000000d0  f0 0e 00 00 01 00 00 00  50 00 00 00 00 00 00 00  |........P.......|
000000e0  f0 0e 00 00 04 00 00 00  00 00 00 00 00 00 00 00  |................|
000000f0  00 04 00 80 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000100  5f 5f 73 74 75 62 73 00  00 00 00 00 00 00 00 00  |__stubs.........|
00000110  5f 5f 54 45 58 54 00 00  00 00 00 00 00 00 00 00  |__TEXT..........|
00000120  40 0f 00 00 01 00 00 00  06 00 00 00 00 00 00 00  |@...............|
00000130  40 0f 00 00 01 00 00 00  00 00 00 00 00 00 00 00  |@...............|
00000140  08 04 00 80 00 00 00 00  06 00 00 00 00 00 00 00  |................|
00000150  5f 5f 73 74 75 62 5f 68  65 6c 70 65 72 00 00 00  |__stub_helper...|
00000160  5f 5f 54 45 58 54 00 00  00 00 00 00 00 00 00 00  |__TEXT..........|
00000170  48 0f 00 00 01 00 00 00  1a 00 00 00 00 00 00 00  |H...............|
00000180  48 0f 00 00 02 00 00 00  00 00 00 00 00 00 00 00  |H...............|
00000190  00 04 00 80 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000001a0  5f 5f 63 73 74 72 69 6e  67 00 00 00 00 00 00 00  |__cstring.......|
000001b0  5f 5f 54 45 58 54 00 00  00 00 00 00 00 00 00 00  |__TEXT..........|
000001c0  62 0f 00 00 01 00 00 00  41 00 00 00 00 00 00 00  |b.......A.......|
000001d0  62 0f 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |b...............|
000001e0  02 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000001f0  5f 5f 75 6e 77 69 6e 64  5f 69 6e 66 6f 00 00 00  |__unwind_info...|
00000200  5f 5f 54 45 58 54 00 00  00 00 00 00 00 00 00 00  |__TEXT..........|
00000210  a4 0f 00 00 01 00 00 00  50 00 00 00 00 00 00 00  |........P.......|
00000220  a4 0f 00 00 02 00 00 00  00 00 00 00 00 00 00 00  |................|
00000230  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000240  19 00 00 00 e8 00 00 00  5f 5f 44 41 54 41 00 00  |........__DATA..|
00000250  00 00 00 00 00 00 00 00  00 10 00 00 01 00 00 00  |................|
00000260  00 10 00 00 00 00 00 00  00 10 00 00 00 00 00 00  |................|
00000270  00 10 00 00 00 00 00 00  07 00 00 00 03 00 00 00  |................|
00000280  02 00 00 00 00 00 00 00  5f 5f 6e 6c 5f 73 79 6d  |........__nl_sym|
00000290  62 6f 6c 5f 70 74 72 00  5f 5f 44 41 54 41 00 00  |bol_ptr.__DATA..|
000002a0  00 00 00 00 00 00 00 00  00 10 00 00 01 00 00 00  |................|
000002b0  10 00 00 00 00 00 00 00  00 10 00 00 03 00 00 00  |................|
000002c0  00 00 00 00 00 00 00 00  06 00 00 00 01 00 00 00  |................|
000002d0  00 00 00 00 00 00 00 00  5f 5f 6c 61 5f 73 79 6d  |........__la_sym|
000002e0  62 6f 6c 5f 70 74 72 00  5f 5f 44 41 54 41 00 00  |bol_ptr.__DATA..|
000002f0  00 00 00 00 00 00 00 00  10 10 00 00 01 00 00 00  |................|
00000300  08 00 00 00 00 00 00 00  10 10 00 00 03 00 00 00  |................|
00000310  00 00 00 00 00 00 00 00  07 00 00 00 03 00 00 00  |................|
00000320  00 00 00 00 00 00 00 00  19 00 00 00 48 00 00 00  |............H...|
00000330  5f 5f 4c 49 4e 4b 45 44  49 54 00 00 00 00 00 00  |__LINKEDIT......|
00000340  00 20 00 00 01 00 00 00  00 10 00 00 00 00 00 00  |. ..............|
00000350  00 20 00 00 00 00 00 00  20 01 00 00 00 00 00 00  |. ...... .......|
00000360  07 00 00 00 01 00 00 00  00 00 00 00 00 00 00 00  |................|
00000370  22 00 00 80 30 00 00 00  00 20 00 00 08 00 00 00  |"...0.... ......|
00000380  08 20 00 00 18 00 00 00  00 00 00 00 00 00 00 00  |. ..............|
00000390  20 20 00 00 10 00 00 00  30 20 00 00 30 00 00 00  |  ......0 ..0...|
000003a0  02 00 00 00 18 00 00 00  68 20 00 00 06 00 00 00  |........h ......|
000003b0  d8 20 00 00 48 00 00 00  0b 00 00 00 50 00 00 00  |. ..H.......P...|
000003c0  00 00 00 00 02 00 00 00  02 00 00 00 02 00 00 00  |................|
000003d0  04 00 00 00 02 00 00 00  00 00 00 00 00 00 00 00  |................|
000003e0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000003f0  c8 20 00 00 04 00 00 00  00 00 00 00 00 00 00 00  |. ..............|
00000400  00 00 00 00 00 00 00 00  0e 00 00 00 20 00 00 00  |............ ...|
00000410  0c 00 00 00 2f 75 73 72  2f 6c 69 62 2f 64 79 6c  |..../usr/lib/dyl|
00000420  64 00 00 00 00 00 00 00  1b 00 00 00 18 00 00 00  |d...............|
00000430  e6 03 ce a5 56 fa 32 2e  b4 ad ee 93 51 18 57 b9  |....V.2.....Q.W.|
00000440  24 00 00 00 10 00 00 00  00 0d 0a 00 00 0d 0a 00  |$...............|
00000450  2a 00 00 00 10 00 00 00  00 00 00 00 00 00 00 00  |*...............|
00000460  28 00 00 80 18 00 00 00  f0 0e 00 00 00 00 00 00  |(...............|
00000470  00 00 00 00 00 00 00 00  0c 00 00 00 38 00 00 00  |............8...|
00000480  18 00 00 00 02 00 00 00  00 00 e4 04 00 00 01 00  |................|
00000490  2f 75 73 72 2f 6c 69 62  2f 6c 69 62 53 79 73 74  |/usr/lib/libSyst|
000004a0  65 6d 2e 42 2e 64 79 6c  69 62 00 00 00 00 00 00  |em.B.dylib......|
000004b0  26 00 00 00 10 00 00 00  60 20 00 00 08 00 00 00  |&.......` ......|
000004c0  29 00 00 00 10 00 00 00  68 20 00 00 00 00 00 00  |).......h ......|
000004d0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00000ef0  55 48 89 e5 48 83 ec 10  c7 45 fc 00 00 00 00 e9  |UH..H....E......|
00000f00  0f 00 00 00 42 61 72 72  79 20 57 61 6c 6b 65 72  |....Barry Walker|
00000f10  21 0a 00 90 48 8d 3d 47  00 00 00 b0 00 e8 1e 00  |!...H.=G........|
00000f20  00 00 48 8d 3d 5e 00 00  00 89 45 f8 b0 00 e8 0d  |..H.=^....E.....|
00000f30  00 00 00 31 c9 89 45 f4  89 c8 48 83 c4 10 5d c3  |...1..E...H...].|
00000f40  ff 25 ca 00 00 00 00 00  4c 8d 1d b9 00 00 00 41  |.%......L......A|
00000f50  53 ff 25 a9 00 00 00 90  68 00 00 00 00 e9 e6 ff  |S.%.....h.......|
00000f60  ff ff 54 68 69 73 20 73  68 6f 75 6c 64 20 62 65  |..This should be|
00000f70  20 69 6e 20 74 68 65 20  64 61 74 61 20 73 65 63  | in the data sec|
00000f80  74 69 6f 6e 2e 0a 00 54  65 73 74 69 6e 67 20 74  |tion...Testing t|
00000f90  68 65 20 68 69 64 64 65  6e 20 73 74 72 69 6e 67  |he hidden string|
00000fa0  2e 0a 00 00 01 00 00 00  1c 00 00 00 00 00 00 00  |................|
00000fb0  1c 00 00 00 00 00 00 00  1c 00 00 00 02 00 00 00  |................|
00000fc0  f0 0e 00 00 34 00 00 00  34 00 00 00 41 0f 00 00  |....4...4...A...|
00000fd0  00 00 00 00 34 00 00 00  03 00 00 00 0c 00 02 00  |....4...........|
00000fe0  14 00 02 00 00 00 00 01  14 00 00 00 00 00 00 00  |................|
00000ff0  00 00 00 01 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00001000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00001010  58 0f 00 00 01 00 00 00  00 00 00 00 00 00 00 00  |X...............|
00001020  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00002000  11 22 10 51 00 00 00 00  11 40 64 79 6c 64 5f 73  |.".Q.....@dyld_s|
00002010  74 75 62 5f 62 69 6e 64  65 72 00 51 72 00 90 00  |tub_binder.Qr...|
00002020  72 10 11 40 5f 70 72 69  6e 74 66 00 90 00 00 00  |r..@_printf.....|
00002030  00 01 5f 00 05 00 02 5f  6d 68 5f 65 78 65 63 75  |.._...._mh_execu|
00002040  74 65 5f 68 65 61 64 65  72 00 21 6d 61 69 6e 00  |te_header.!main.|
00002050  25 02 00 00 00 03 00 f0  1d 00 00 00 00 00 00 00  |%...............|
00002060  f0 1d 14 0f 00 00 00 00  35 00 00 00 0e 01 00 00  |........5.......|
00002070  04 0f 00 00 01 00 00 00  3d 00 00 00 0e 01 00 00  |........=.......|
00002080  13 0f 00 00 01 00 00 00  02 00 00 00 0f 01 10 00  |................|
00002090  00 00 00 00 01 00 00 00  16 00 00 00 0f 01 00 00  |................|
000020a0  f0 0e 00 00 01 00 00 00  1c 00 00 00 01 00 00 01  |................|
000020b0  00 00 00 00 00 00 00 00  24 00 00 00 01 00 00 01  |........$.......|
000020c0  00 00 00 00 00 00 00 00  04 00 00 00 05 00 00 00  |................|
000020d0  00 00 00 40 04 00 00 00  20 00 5f 5f 6d 68 5f 65  |...@.... .__mh_e|
000020e0  78 65 63 75 74 65 5f 68  65 61 64 65 72 00 5f 6d  |xecute_header._m|
000020f0  61 69 6e 00 5f 70 72 69  6e 74 66 00 64 79 6c 64  |ain._printf.dyld|
00002100  5f 73 74 75 62 5f 62 69  6e 64 65 72 00 75 73 65  |_stub_binder.use|
00002110  6c 65 73 73 00 67 65 74  6f 75 74 00 00 00 00 00  |less.getout.....|
00002120
AMIGA:amiga~/Desktop/Code/C> _

Note the hex number 90 after the "Barry Walker![newline][EOF]" is the NOP instruction...
Hope this helps...
EDIT:

00000ef0  55 48 89 e5 48 83 ec 10  c7 45 fc 00 00 00 00 e9  |UH..H....E......|
00000f00  0f 00 00 00 42 61 72 72  79 20 57 61 6c 6b 65 72  |....Barry Walker|

The JMP instruction is at the end of the upper line and is this:
e9 0f 00 00 00 followed by the characters.
'e9' is jmp op-code.
'0f' is the little endian number of bytes, (from a signed 32 bit number), 15 decimal, to jump to the end-of-file/null byte '00' to execute the nop op-code.
Hope this helps too.