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Message-ID: <89da6560807291624he0cb2d1u696542e552887e8d@mail.gmail.com>
Date: Tue, 29 Jul 2008 16:24:36 -0700
From: "Lael Jones" <lael DOT jones AT gmail DOT com>
To: djgpp AT delorie DOT com
Subject: djgpp v2 : Control register access segfaults
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Reply-To: djgpp AT delorie DOT com

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Hello,

I'm upgrading my application from djgpp v1 to djgpp v2 and am seeing a seg
fault in the debug build when the application tries to access (read or
write) control registers (specifically CR4).  The inline assembly I am using
is:

   // Enable SSE instructions via OSFXSR (bit 9 of CR4).
   __asm__ __volatile__
   (
      "
         movl %%cr4, %%eax
         orl  $0x00000200, %%eax
         movl %%eax, %%cr4
      "
      :  /* output */
      :  /* input */
      :  /* modified */
      "%eax"
   );

The seg fault always occurs on "movl %%cr4, %%eax".  The exact same code
executes without the seg fault in a release build ("-O2").  The relevant
source file is compiled with "-ggdb -O0", however due to the size of the
executable I have stripped the debug symbols using "strip -g".  All
libraries are statically linked.

Are there any known issues/changes to djgpp that would cause this?

I searched both google and mailing list archives and wasn't able to find any
reference to this issue.

Thanks

Lael

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<div dir="ltr"><div>Hello, </div>
<div>&nbsp;</div>
<div>I&#39;m upgrading my application from djgpp v1 to djgpp v2 and am seeing a seg fault in the debug build when the application tries to access (read or write) control registers (specifically CR4).&nbsp; The inline assembly I am using is:</div>

<div>&nbsp;</div>
<div>&nbsp;&nbsp; // Enable SSE instructions via OSFXSR (bit 9 of CR4).<br>&nbsp;&nbsp; __asm__ __volatile__<br>&nbsp;&nbsp; (<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &quot;<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; movl %%cr4, %%eax<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; orl&nbsp; $0x00000200, %%eax<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; movl %%eax, %%cr4<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &quot;<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; :&nbsp; /* output */<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; :&nbsp; /* input */<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; :&nbsp; /* modified */<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &quot;%eax&quot;<br>&nbsp;&nbsp; );</div>
<div>&nbsp;</div>
<div>The seg fault always occurs on &quot;movl %%cr4, %%eax&quot;.&nbsp; The exact same code executes without the seg fault in a release build (&quot;-O2&quot;).&nbsp; The relevant source file is compiled with &quot;-ggdb -O0&quot;, however due to the size of the executable I have stripped the debug symbols using &quot;strip -g&quot;.&nbsp; All libraries are statically linked.</div>

<div>&nbsp;</div>
<div>Are there any known issues/changes to djgpp that would cause this?&nbsp;</div>
<div>&nbsp;</div>
<div>I searched both google and mailing list archives and wasn&#39;t able to find any reference to this issue.</div>
<p>Thanks</p>
<div>&nbsp;</div>
<div>Lael</div>
<div><br></div></div>

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