How to call malloc in x86_64 asm

Question

I am trying to call malloc in Visual Studio Community 2019 assembly but I keep getting undefined reference to symbol malloc.

mov rcx,10h
call malloc

Does not compile as I get the undefined reference to malloc I have even tried it with _malloc with the same issue. Am I missing some sort of include?

This would be a better question if you quoted the *exact* error message, so it was clear it was from the assembler, not at link time. (If you declared `extern malloc` but then didn't link with the C library, you'd expect some kind of undefined reference when linking, after assembling successfully.) — Peter Cordes, Oct 21 '20 at 03:20

score 2 · Accepted Answer · answered Oct 21 '20 at 00:53

2

This was solved by putting an extern in the data section

.data
extern malloc: proc
.code 
;Some code;

answered Oct 21 '20 at 00:53

BackSpace7777777

If this actually solved your problem you should accept your answer! – Marco Bonelli Oct 21 '20 at 00:59
I have to wait 2 days – BackSpace7777777 Oct 21 '20 at 01:57
Oh, my bad then. I forgot the wait time was so long. Never mind. – Marco Bonelli Oct 21 '20 at 01:57
1

Are you sure the `extern malloc: proc` has to be in `.data`? That seems odd, unless that creates a placeholder for dynamic linking (a pointer for indirect call) at the position you declare it. I don't use MASM, but in other assemblers for other OSes, e.g. NASM, `extern malloc` could be anywhere and is just a directive that has no interaction with the current section. – Peter Cordes Oct 21 '20 at 03:19

1 Answers1