CODEWITHSUNDEEP
visual-studiomasm
asasdasd123
asasdasd123

Reputation: 39

undefined symbol: rax in Visual Studio MASM

i am using assembly to get the address to the process' PEB, but i cant compile it.

this is the x64 asm code, but it gives me the error "undefined symbol: rax" which makes no sense. doesnt even matter if i compile it in x86 or x64. i have a separate .asm file that has the same function but with x86 registers and such.

.386
.model flat, C

.code

get_peb_internal_x64 proc
    assume gs:nothing
    mov rax, gs:[60h]
    ret
get_peb_internal_x64 endp

end

-- now the x86 version that does compile always 

.386
.model flat, C

.code

get_peb_internal_x86 proc
    assume fs:nothing
    mov eax, fs:[30h]
    ret
get_peb_internal_x86 endp

end

Upvotes: 1

Views: 2497

Answers (1)

asasdasd123
asasdasd123

Reputation: 39

I have solved my issue thanks to @MichaelPetch

The problem was caused by the fact that i had the .model and .386 directives that apparently as ive read myself just now, arent used in x64 masm, and also the assume gs:nothing.

I have adapted my code into a single file and it ended up this way:

ifdef rax
else
.386
.model flat, C
endif

.code

ifdef rax

get_peb_internal_x64 proc
mov rax, gs:[60h]
    ret
get_peb_internal_x64 endp

else

get_peb_internal_x86 proc
assume fs:nothing
    mov eax, fs:[30h]
    ret
get_peb_internal_x86 endp

endif

end

Upvotes: 2

Related Questions