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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Few questions regarding pxe_start_nbp function (arch/i386/interface/pxe/pxe_call.c) - inline asm code:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="mso-list:Ignore">1.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]><span dir="LTR"></span>Why STI command is used ? <o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="mso-list:Ignore">2.<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]><span dir="LTR"></span>Why we have “esi” & “ebp” At the clobber list ( ::: XXX) ? , using real mode debugger I noticed that esi , ebp values have changed prior to 0x7c00 far call:<o:p></o:p></p>
<p class="MsoListParagraph"><o:p> </o:p></p>
<p class="MsoListParagraph"><b><i><span style="color:#0070C0">EAX=00000000 EBX=00000AA0 ECX=000A9300 EDX=00093AA0<o:p></o:p></span></i></b></p>
<p class="MsoListParagraph"><b><i><span style="color:#0070C0">ESI=422E2B30 EDI=00000A40 EBP=00000007 ESP=00002D12 EIP=0000030E<o:p></o:p></span></i></b></p>
<p class="MsoListParagraph"><b><i><span style="color:#0070C0">CS=9300 DS=93AE ES=9300 FS=93AE GS=93AE SS=93AE C=0 Z=0 D=0 I=1 S=0<o:p></o:p></span></i></b></p>
<p class="MsoListParagraph"><b><i><span style="color:#0070C0"><o:p> </o:p></span></i></b></p>
<p class="MsoListParagraph"><b><i><span style="color:#0070C0">9300:030E CALL FAR 0000:7C00<o:p></o:p></span></i></b></p>
<p class="MsoListParagraph"><b><i><span style="color:#0070C0">9300:0313 ADD SP,0004<o:p></o:p></span></i></b></p>
<p class="MsoListParagraph"><b><i><span style="color:#0070C0">9300:0316 RET<o:p></o:p></span></i></b></p>
<p class="MsoListParagraph"><o:p> </o:p></p>
<p class="MsoListParagraph">As you can see – cx holds the code segment , EDI & EBX holds !PXE & PXENV+ addresses and ESI , EBP values are not clear (at least to me). I would expect ESI value to equal ECX as first asm command is (in the inline asm ) :
<b><i><span style="color:#0070C0">"movw %%cx, %%es\n\t", </span></i></b><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Your help,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Yossi<o:p></o:p></p>
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