OSDev.org

Posted: **Thu Jan 31, 2019 6:56 pm**

I'm trying to enable paging. For some reason, I keep getting this error:

make[1]: Entering directory '/mnt/c/Users/tim21/Projects/firststep/arch/i686'
i686-elf-as paging_init.s -o paging_init.o
paging_init.s: Assembler messages:
paging_init.s:17: Error: operand type mismatch for `mov'
Makefile:14: recipe for target 'paging_init.o' failed
make[1]: *** [paging_init.o] Error 1
make[1]: Leaving directory '/mnt/c/Users/tim21/Projects/firststep/arch/i686'
Makefile:28: recipe for target 'arch.o' failed
make: *** [arch.o] Error 2

here is my assembly code:

Code: Select all

.section .text

.global loadPageDirectory
loadPageDirectory:
    push %ebp
    mov %esp, %ebp
    mov 8(%esp), %eax
    mov %eax, %cr3
    mov %ebp, %esp
    pop %ebp
    ret

.global enablePaging
enablePaging:
    push %ebp
    mov %esp, %ebp
    mov %cr0, $eax
    or $0x80000000, %eax
    mov %eax, %cr0
    mov %ebp, %esp
    pop %ebp
    ret

Can anyone help me with this?

Posted: **Thu Jan 31, 2019 7:11 pm**

MakaAlbarn001 wrote:I'm trying to enable paging. For some reason, I keep getting this error:
Code: Select all
paging_init.s:17: Error: operand type mismatch for `mov'

In cases like these, always examine what the tool is trying to point out to you. Look closely at line 17, and then compare it to line 18. Pay attention in particular to the prefix symbols.

Posted: **Fri Feb 01, 2019 12:41 am**

"$eax"?

Posted: **Fri Feb 01, 2019 12:45 am**

Yes, it should be %eax, not $eax

Posted: **Fri Feb 01, 2019 8:05 am**

Since you are dealing with AT&T assembly style, it is imperative to use the correct mnemonics: movl, movw or movb instead of mov.

The same applies to push/pop, "or", ...

And, of course, as pointed out: $eax is wrong too.

Posted: **Fri Feb 01, 2019 8:58 am**

fpissarra wrote:Since you are dealing with AT&T assembly style, it is imperative to use the correct mnemonics: movl, movw or movb instead of mov.

Not really. When the assembler can infer the operand size from the operands, you may use "mov" without a suffix.

Posted: **Fri Feb 01, 2019 11:48 am**

Octocontrabass wrote:Not really. When the assembler can infer the operand size from the operands, you may use "mov" without a suffix.

My personal coding preference when using AT&T syntax isn't to use the instruction suffixes unless they can't be inferred.

OSDev.org

mov operand type mismatch problem

mov operand type mismatch problem

Re: mov operand type mismatch problem

Re: mov operand type mismatch problem

Re: mov operand type mismatch problem

Re: mov operand type mismatch problem

Re: mov operand type mismatch problem

Re: mov operand type mismatch problem