How to Dynamically Allocate Memory Using Assembly and System Calls Under Linux

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On Linux mmap2 is a sensible system call to use for this at a low level. It takes 6 arguments, so in IA32 you can call it using:

    mov eax, 192    ; mmap2
    xor ebx, ebx    ; addr = NULL
    mov ecx, 4096   ; len = 4096
    mov edx, $7     ; prot = PROT_READ|PROT_WRITE|PROT_EXEC
    mov esi, $22    ; flags = MAP_PRIVATE|MAP_ANONYMOUS
    mov edi, -1     ; fd = -1
    xor ebp, ebp    ; offset = 0 (4096*0)
    int $80         ; make call

(See the relevant kernel source for details on the parameter passing)

I built this with NASM and verified it worked using strace, which produced:

mmap2(NULL, 4096, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xf77ae000

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