-1
endbr64:

push rbp

mov rbp,rsp

push rbx

sub rsp,0x18

mov DWORD PTR [rbp-0x14],edi

cmp DWORD PTR [rbp-0x14],0x0

je 0x1185 <fib+28>

cmp DWORD PTR [rbp-0x14],0x1

jne 0x118c <fib+35>

mov eax,0x1

jmp 0x11aa <fib+65>

mov eax,DWORD PTR [rbp-0x14]

sub eax,0x1

mov edi,eax

call 0x1169 <fib>

mov ebx,eax

mov eax,DWORD PTR [rbp-0x14]

sub eax,0x2

mov edi,eax

call 0x1169 <fib>

add eax,ebx

add rsp,0x18

pop rbx

pop rbp

ret

main:

endbr64

push rbp

rbp,rsp

mov rax,QWORD PTR [rip+0x2e50] # 0x4010 <stdout@@GLIBC_2.2.5>

mov esi,0x0

mov rdi,rax

call 0x1060 <setbuf@plt>

mov edi,0x1c

call 0x1169 <fib>

mov esi,eax

lea rdi,[rip+0xe24] # 0x2004

mov eax,0x0

call 0x1070 <printf@plt>

mov eax,0x0

pop rbp

ret
Peter Cordes
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1 Answers1

1

PTR is MASM syntax, and originally wasn't support by NASM (mostly because MASM syntax is inconsistent and harder to read).

Recently NASM developers added code to detect if PTR is used and warn people if it is, so that if people mistakenly try to use MASM syntax when the assembler is expecting NASM syntax they have a better idea of why things went wrong. This warning is enabled by default. The warning can be disabled (-w-ptr) if you want things to go wrong instead.

There are 2 solutions that make sense:

a) convert the code into NASM syntax (e.g. mov DWORD PTR [rbp-0x14],edi would become mov [rbp-0x14],edi).

b) Enable the (new, experimental, partial) "masm compatibility" package (put the %use masm directive at the start of the code). This may not work well because some things (e.g. mov eax,foo) depend on how the symbol was defined, which isn't information that NASM tracks (consistent syntax means that it never needed that information to begin with) making it ambiguous (possibly assembled wrong).

Brendan
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  • Note that no NASM options are going to help you compile `objdump` output like `call 0x1060 ` without at least a bit of thought on the user's part. `objconv` can disassemble into NASM that's ready to assemble. – Peter Cordes Apr 23 '21 at 11:09
  • `%use masm` is a useful suggestion, might be good to post that as an answer on [x86, difference between BYTE and BYTE PTR](https://stackoverflow.com/q/13790146). We already have [warning: \`PTR' is not a NASM keyword \[-w+ptr\]](https://stackoverflow.com/q/66487318) as a signpost, this question doesn't look like it has any future value except for your answer (which like I said could go elsewhere) – Peter Cordes Apr 23 '21 at 11:12