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Index > Compiler Internals > [bug] crash while compiling sample (fasm v1.73.30)

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vityacv



Joined: 27 Oct 2012
Posts: 5
vityacv 12 Jul 2023, 06:41
stub64.asm:
Code:
format binary 
use64 
struct IMAGE_DOS_HEADER
e_magic rw 1 
e_cblp rw 1
e_cp rw 1
e_crlc rw 1
e_cparhdr rw 1 
e_minalloc rw 1
e_maxalloc rw 1
e_ss rw 1
e_sp rw 1
e_csum rw 1
e_ip rw 1
e_cs rw 1
e_lfarlc rw 1
e_ovno rw 1
e_res rw 4 
e_oemid rw 1 
e_oeminfo rw 1 
e_res2 rw 10 
e_lfanew rd 1
ends 

teste IMAGE_DOS_HEADER 'MZ',testq.size,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,testq.size 

testq:
mov rax,1 
align 4 
testq.size = $-teste
    

test64.asm:
Code:
format pe64 on 'stub64.bin' 
entry Main
Main: 
ret 
    

results in
Code:
---------------------------                                                                                                             
fasm.exe - Application Error                                                                                                            
---------------------------                                                                                                             
The instruction at 0x0000000000419994 referenced memory at 0x0000000040B10000. The memory could not be written.                         
                                                                                                                                        
                                                                                                                                        
Click on OK to terminate the program                                                                                                    
---------------------------                                                                                                             
OK                                                                                                                                      
---------------------------     
Post 12 Jul 2023, 06:41
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 20067
Location: In your JS exploiting you and your system
revolution 12 Jul 2023, 07:58
Your stub.asm does not assemble.
Code:
flat assembler  version 1.73.30  (16384 kilobytes memory)memory)
stub64.asm [3]:
struct IMAGE_DOS_HEADER
processed: struct IMAGE_DOS_HEADER
error: illegal instruction.    
Post 12 Jul 2023, 07:58
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 20067
Location: In your JS exploiting you and your system
revolution 12 Jul 2023, 08:07
I changed stub64.asm to this:
Code:
format binary
use64
teste:  e_magic         db      'MZ'
        e_cblp          dw      testq.size
        e_cp            rw      1
        e_crlc          rw      1
        e_cparhdr       rw      1
        e_minalloc      rw      1
        e_maxalloc      rw      1
        e_ss            rw      1
        e_sp            rw      1
        e_csum          rw      1
        e_ip            rw      1
        e_cs            rw      1
        e_lfarlc        rw      1
        e_ovno          rw      1
        e_res           rw      1
        e_oemid         rw      1
        e_oeminfo       rw      1
        e_res2          rw      10
        e_lfanew        dd      testq.size

testq:
mov rax,1
align 4
testq.size = $-teste    
Now I can reproduce your resutl:
Code:
flat assembler  version 1.73.30  (16384 kilobytes memory)
Segmentation fault (core dumped)    
Post 12 Jul 2023, 08:07
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 20067
Location: In your JS exploiting you and your system
revolution 12 Jul 2023, 08:24
In formats.inc around line 742 we can add one line:
Code:
;...
        call    lseek
        movzx   ecx,word [esi+4]
        dec     ecx
js out_of_memory  ; <--- add this line
        shl     ecx,9
        movzx   edx,word [esi+2]
        test    edx,edx
        jnz     stub_header_size_ok
;...    
Jumping to out_of_memory isn't really correct, but there is no dedicated error message to indicate a malformed stub file. At least it won't crash, it prints out of memory instead.
Post 12 Jul 2023, 08:24
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 20067
Location: In your JS exploiting you and your system
revolution 12 Jul 2023, 16:17
No crash in 1.73.31
Code:
flat assembler  version 1.73.31  (16384 kilobytes memory)
error: out of memory.    
Post 12 Jul 2023, 16:17
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