Posix_memalign

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sakkiesalm

Joined: 07 Feb 2011
Posts: 9

sakkiesalm 02 Oct 2015, 12:01

Hi

What is wrong with this code ? ,why does it give me a "Program received signal SIGSEGV, Segmentation fault." error

I allocate 134217728 bytes in 128 byte alignment

Code:

  hashkeymask equ 134217727     
            hashsize equ 134217728

            lea rdi,[HashBuffer]
            mov rsi,128
            mov rdx,hashsize
            call posix_memalign
            mov rax,[HashBuffer]
            mov [HashBuffer + hashsize - 256],45

Why can't i allocate the memory,although it is less than the memory i have set aside/allocated ?

02 Oct 2015, 12:01

JohnFound

Joined: 16 Jun 2003
Posts: 3499
Location: Bulgaria

JohnFound 02 Oct 2015, 12:22

Why not to run it in a debugger and see on what instruction you get segmentation fault?
If you are importing posix_memalign from a dynamic library, you should call it indirectly:

Code:

call [posix_memalign]

P.S. It is a bad style IMHO to use "EQU" for numeric constants. Use "=" instead. In FASM these two are not equal.

02 Oct 2015, 12:22

sakkiesalm

Joined: 07 Feb 2011
Posts: 9

sakkiesalm 02 Oct 2015, 12:31

JohnFound wrote:

Why not to run it in a debugger and see on what instruction you get segmentation fault?
If you are importing posix_memalign from a dynamic library, you should call it indirectly:
Code:
call [posix_memalign]    
P.S. It is a bad style IMHO to use "EQU" for numeric constants. Use "=" instead. In FASM these two are not equal.

hi,thanks

Yes i did run it in debugger and i get error when accessing that memory part

Code:

mov [HashBuffer + hashsize - 256],45

If i use a smaller number for example

Code:

mov [HashBuffer + 1000000 - 256],45

i do not get an error.But why cannot i use the whole allocated amount ?
I tried = also now still same error

I did check,memory gets allocated correctly,in task manager after running

Code:

call posix_memalign

02 Oct 2015, 12:31

ProphetOfDoom

Joined: 08 Aug 2008
Posts: 120
Location: UK

ProphetOfDoom 02 Oct 2015, 23:12

Hi sakkiesalm,

It looks like you are treating HashBuffer as a pointer when really it's a pointer to a pointer. You had the right idea when you moved the result into rax. Try replacing the segfaulting line with this:

Code:

mov qword [rax + hashsize - 256], 45

02 Oct 2015, 23:12

sakkiesalm

Joined: 07 Feb 2011
Posts: 9

sakkiesalm 03 Oct 2015, 04:34

ProphetOfDoom wrote:

Hi sakkiesalm,

It looks like you are treating HashBuffer as a pointer when really it's a pointer to a pointer. You had the right idea when you moved the result into rax. Try replacing the segfaulting line with this:
Code:
mov qword [rax + hashsize - 256], 45    

hi ProphetOfDoom

Thank you,that seems to solve the problem! Smile

03 Oct 2015, 04:34

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