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CandyMan



Joined: 04 Sep 2009
Posts: 345
Location: film "CandyMan" directed through Bernard Rose OR Candy Shop
CandyMan
How to detect the address where the program was loaded (its first byte address)? I am asking for a way for Linux and Haiku (assembler or pascal code is welcome).

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smaller is better
Post 25 Dec 2021, 00:35
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redsock



Joined: 09 Oct 2009
Posts: 377
Location: Australia
redsock
HeavyThing code:
Code:
include '../ht_defaults.inc'
include '../ht.inc'

public _start
falign
_start:
        call    ht$init

        mov     edi, .codeseg
        call    string$to_stdout

        mov     edi, ht$codeseg
        mov     esi, 16
        call    string$from_unsigned
        push    rax
        mov     rdi, rax
        call    string$to_stdoutln
        pop     rdi
        call    heap$free

        mov     edi, .loadaddr
        call    string$to_stdout

        mov     edi, _start
        mov     esi, 16
        call    string$from_unsigned
        push    rax
        mov     rdi, rax
        call    string$to_stdoutln
        pop     rdi
        call    heap$free


        mov     edi, .dsaddr
        call    string$to_stdout

        mov     rdi, ht$dataseg
        mov     esi, 16
        call    string$from_unsigned
        push    rax
        mov     rdi, rax
        call    string$to_stdoutln
        pop     rdi
        call    heap$free

        mov     eax, syscall_exit
        xor     edi, edi
        syscall
cleartext .codeseg, 'code segment is at: 0x'
cleartext .loadaddr, '_start is at: 0x'
cleartext .dsaddr, 'data segment is at: 0x'

include '../ht_data.inc'
    
Produces:
Code:
# ./test
code segment is at: 0x4000b0
_start is at: 0x401740
data segment is at: 0x4018e0
    
and this of course matches the ELF sections from thje binary:
Code:
# objdump -dx -M intel ./test |more

./test:     file format elf64-x86-64
./test
architecture: i386:x86-64, flags 0x00000112:
EXEC_P, HAS_SYMS, D_PAGED
start address 0x0000000000401740

Program Header:
    LOAD off    0x0000000000000000 vaddr 0x0000000000400000 paddr 0x0000000000400000 align 2**21
         filesz 0x00000000000018e0 memsz 0x00000000000018e0 flags r-x
    LOAD off    0x00000000000018e0 vaddr 0x00000000006018e0 paddr 0x00000000006018e0 align 2**21
         filesz 0x0000000000000160 memsz 0x0000000000000160 flags rw-

Sections:
Idx Name          Size      VMA               LMA               File off  Algn
  0 .text         00001830  00000000004000b0  00000000004000b0  000000b0  2**4
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
  1 .data         00000160  00000000006018e0  00000000006018e0  000018e0  2**4
                  CONTENTS, ALLOC, LOAD, DATA
    

Is this what you were after?

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2 Ton Digital - https://2ton.com.au/
Post 25 Dec 2021, 20:09
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ProMiNick



Joined: 24 Mar 2012
Posts: 656
Location: Russian Federation, Sochi
ProMiNick
Quote:
data segment is at: 0x4018e0

Quote:
# objdump -dx -M intel ./test |more
...
Code:
Program Header:
    ...
    LOAD off    0x00000000000018e0 vaddr 0x00000000006018e0 paddr 0x00000000006018e0 align 2**21
         ...

Sections:
Idx Name          Size      VMA               LMA               File off  Algn
  ...
  1 .data         00000160  00000000006018e0  00000000006018e0    


redsock, why solutions are think different about data segment/section
Post 25 Dec 2021, 20:56
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redsock



Joined: 09 Oct 2009
Posts: 377
Location: Australia
redsock
ProMiNick wrote:
redsock, why solutions are think different about data segment/section
Excellent question, I should have looked closer at the outputs after I quickly threw the previous example together. As it turns out, this is because of the way I coded the symbol for ht$dataseg in https://2ton.com.au/library_as_html/ht_data.inc.html, where you can see that I declared the symbol right before the actual data section begins. I replaced the ht_data.inc file with:
Code:
        ; ------------------------------------------------------------------------
        ;       
        ; ht_data.inc: globals macro to define a global writeable data segment
        ;
        ; to use: globals {
        ;       someglobal dq 0
        ; }
        ; anywhere throughout your code, and it will all end up inside our single datasegment
        ;
        ; this is meant to be included _last_ (and our marker here defines the end of
        ; the code section)

ht$dataseg = $

        section '.data' writeable align 16
ht$actual_dataseg = $
        globalVars

    
and updated my test.asm:
Code:
include '../ht_defaults.inc'
include '../ht.inc'

globals
{
        _dsaddr dq      0
}

public _start
falign
_start:
        call    ht$init

        mov     edi, .codeseg
        call    string$to_stdout

        mov     edi, ht$codeseg
        mov     esi, 16
        call    string$from_unsigned
        push    rax
        mov     rdi, rax
        call    string$to_stdoutln
        pop     rdi
        call    heap$free

        mov     edi, .loadaddr
        call    string$to_stdout

        mov     edi, _start
        mov     esi, 16
        call    string$from_unsigned
        push    rax
        mov     rdi, rax
        call    string$to_stdoutln
        pop     rdi
        call    heap$free


        mov     edi, .dsaddr
        call    string$to_stdout

        mov     rdi, ht$dataseg
        mov     esi, 16
        call    string$from_unsigned
        push    rax
        mov     rdi, rax
        call    string$to_stdoutln
        pop     rdi
        call    heap$free

        mov     edi, .actualds
        call    string$to_stdout

        mov     rdi, ht$actual_dataseg
        mov     esi, 16
        call    string$from_unsigned
        push    rax
        mov     rdi, rax
        call    string$to_stdoutln
        pop     rdi
        call    heap$free

        mov     edi, .postht
        call    string$to_stdout

        mov     rdi, _dsaddr
        mov     esi, 16
        call    string$from_unsigned
        push    rax
        mov     rdi, rax
        call    string$to_stdoutln
        pop     rdi
        call    heap$free

        mov     eax, syscall_exit
        xor     edi, edi
        syscall
cleartext .codeseg, 'code segment is at: 0x'
cleartext .loadaddr, '_start is at: 0x'
cleartext .dsaddr, 'end of code segment is at: 0x'
cleartext .actualds, 'start of data segment is at: 0x'
cleartext .postht, 'after HeavyThing globals, our dataseg is at: 0x'

include '../ht_data.inc'
    
Which now produces:
Code:
# ./test
code segment is at: 0x4000b0
_start is at: 0x401740
end of code segment is at: 0x401ab4
start of data segment is at: 0x601ac0
after HeavyThing globals, our dataseg is at: 0x601c20
    
and that does match correctly the ELF binary inspection:
Code:
# objdump -dx -M intel ./test |more

./test:     file format elf64-x86-64
./test
architecture: i386:x86-64, flags 0x00000112:
EXEC_P, HAS_SYMS, D_PAGED
start address 0x0000000000401740

Program Header:
    LOAD off    0x0000000000000000 vaddr 0x0000000000400000 paddr 0x0000000000400000 align 2**21
         filesz 0x0000000000001ab4 memsz 0x0000000000001ab4 flags r-x
    LOAD off    0x0000000000001ac0 vaddr 0x0000000000601ac0 paddr 0x0000000000601ac0 align 2**21
         filesz 0x0000000000000168 memsz 0x0000000000000168 flags rw-

Sections:
Idx Name          Size      VMA               LMA               File off  Algn
  0 .text         00001a04  00000000004000b0  00000000004000b0  000000b0  2**4
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
  1 .data         00000168  0000000000601ac0  0000000000601ac0  00001ac0  2**4
                  CONTENTS, ALLOC, LOAD, DATA
    
Smile much better.

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2 Ton Digital - https://2ton.com.au/
Post 25 Dec 2021, 21:09
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