How to allocate memory in Linux dynamically (like malloc)

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Ton

Joined: 06 Jan 2005
Posts: 22

Ton 10 Feb 2005, 08:30

Dear all,

In fasm I can allocate memory with e.g.
a0 rd 1024h

But how can I do this dynamically using system calls. Basically I need a
malloc(3), and free(3). I couldn't find the clue in the system call list, there is
no *alloc* there.

Best Regards,
Ton

10 Feb 2005, 08:30

Endre

Joined: 29 Dec 2003
Posts: 215
Location: Budapest, Hungary

Endre 10 Feb 2005, 12:11

You have an excellent example: Take a look into the source of fasm. You will find it.

10 Feb 2005, 12:11

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8466
Location: Kraków, Poland

Tomasz Grysztar 10 Feb 2005, 12:18

It's syscall 45, called sys_brk, which resizes the memory block allocated for your program (the program resides on the bottom of this block, and with sys_brk you just move the top of it).

10 Feb 2005, 12:18

Dryobates

Joined: 13 Jul 2003
Posts: 46
Location: Poland

Dryobates 10 Feb 2005, 16:11

sys_brk is old style. Now it's preffered sys_mmap with anon mapping.

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10 Feb 2005, 16:11

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8466
Location: Kraków, Poland

Tomasz Grysztar 10 Feb 2005, 16:21

However brk syscall is common for the Linux and all BSD systems (I'm not sure about BeOS), so I preferred it.

10 Feb 2005, 16:21

Ton

Joined: 06 Jan 2005
Posts: 22

Ton 10 Feb 2005, 16:52

Thanks for the pointers. Iĺl give it a try.

--
Ton

10 Feb 2005, 16:52

scientica
Retired moderator

Joined: 16 Jun 2003
Posts: 689
Location: Linköping, Sweden

scientica 11 Feb 2005, 12:48

there's also malloc and free in linux Smile

try: man 3 malloc

11 Feb 2005, 12:48

Dryobates

Joined: 13 Jul 2003
Posts: 46
Location: Poland

Dryobates 11 Feb 2005, 22:08

scientica wrote:

there's also malloc and free in linux
try: man 3 malloc

But then he need link with libc...

_________________
There's one more bug... Smile

11 Feb 2005, 22:08

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