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POMalloc and Free multiple arrays in assembly
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copied!<p>I'm trying to experiment with malloc and free in assembly code (NASM, 64 bit).</p> <p>I have tried to malloc two arrays, each with space for 2 64 bit numbers. Now I would like to be able to write to their values (not sure if/how accessing them will work exactly) and then at the end of the whole program or in the case of an error <strong>at any point</strong>, free the memory.</p> <p>What I have now works fine if there is one array but as soon as I add another, it fails on the first attempt to deallocate any memory :(</p> <p>My code is currently the following:</p> <pre><code>extern printf, malloc, free LINUX equ 80H ; interupt number for entering Linux kernel EXIT equ 60 ; Linux system call 1 i.e. exit () segment .text global main main: push dword 16 ; allocate 2 64 bit numbers call malloc add rsp, 4 ; Undo the push test rax, rax ; Check for malloc failure jz malloc_fail mov r11, rax ; Save base pointer for array ; DO SOME CODE/ACCESSES/OPERATIONS HERE push dword 16 ; allocate 2 64 bit numbers call malloc add rsp, 4 ; Undo the push test rax, rax ; Check for malloc failure jz malloc_fail mov r12, rax ; Save base pointer for array ; DO SOME CODE/ACCESSES/OPERATIONS HERE malloc_fail: jmp dealloc ; Finish Up, deallocate memory and exit dealloc: dealloc_1: test r11, r11 ; Check that the memory was originally allocated jz dealloc_2 ; If not, try the next block of memory push r11 ; push the address of the base of the array call free ; Free this memory add rsp, 4 dealloc_2: test r12, r12 jz dealloc_end push r12 call free add rsp, 4 dealloc_end: call os_return ; Exit os_return: mov rax, EXIT mov rdi, 0 syscall </code></pre>

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