Re: x86 assembly question

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On Mon, 8 Sept 2025 at 22:38, Manuel Bouyer <[email protected]> wrote:

> Hello,
> I suspect that some assembly code is not doing what I think it should.
> But as it's in the early stage of boot it's hard to debug.
>
> Here's the (32bits) code:
>         push %ebx /* save start_info to stack */
>         /* do stuff */
>         movl $RELOC(__kernel_end), %ebp
>         addl $3, %ebp
>         andl $~3, %ebp
>         movl 0(%ebp), %eax /* read size */
>         addl %ebp, %eax /* compute esym */
>         /* check if start_info is within symbol table */
>         movl -4(%esp), %ebx
>

it's been many years, but shouldn't it be
    movl 0(%esp), %ebx

to get the saved value? Or some positive offset if other values were pushed
in the meantime?

Cheers,

Joachim

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<div dir=3D"ltr"><div dir=3D"ltr">On Mon, 8 Sept 2025 at 22:38, Manuel Bouy=
er &lt;<a href=3D"mailto:[email protected]">[email protected]</a>=
&gt; wrote:<br></div><div class=3D"gmail_quote gmail_quote_container"><bloc=
kquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left-=
width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);paddin=
g-left:1ex">Hello,<br>
I suspect that some assembly code is not doing what I think it should.<br>
But as it&#39;s in the early stage of boot it&#39;s hard to debug.<br>
<br>
Here&#39;s the (32bits) code:<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 push %ebx /* save start_info to stack */<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 /* do stuff */<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 movl $RELOC(__kernel_end), %ebp<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 addl $3, %ebp<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 andl $~3, %ebp<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 movl 0(%ebp), %eax /* read size */<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 addl %ebp, %eax /* compute esym */<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 /* check if start_info is within symbol table *=
/<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 movl -4(%esp), %ebx<br></blockquote><div><br></=
div><div>it&#39;s been many years, but shouldn&#39;t it be</div><div>=C2=A0=
 =C2=A0 movl 0(%esp), %ebx</div><div><br></div><div>to get the saved value?=
 Or some positive offset if other values were pushed in the meantime?</div>=
<div><br></div><div>Cheers,</div><div><br></div><div>Joachim</div><div>=C2=
=A0</div></div></div>

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