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Fix lot of dead links in both the 2nd and 1st edition
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Philipp Oppermann
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</a><a href="#" class="reply">Antworten</a></div><div class="isso-follow-up"></div></div></div></div></div></div><div id="isso-242" class="isso-comment isso-no-votes"><div class="avatar"><svg version="1.1" viewBox="0 0 48 48" preserveAspectRatio="xMinYMin meet" shape-rendering="crispEdges" data-hash="3773460ec1e4"><rect x="0" y="0" width="56" height="56" style="fill: #f0f0f0"></rect><rect x="4" y="4" width="8" height="8" style="fill: #be5168"></rect><rect x="36" y="4" width="8" height="8" style="fill: #be5168"></rect><rect x="4" y="20" width="8" height="8" style="fill: #be5168"></rect><rect x="36" y="20" width="8" height="8" style="fill: #be5168"></rect><rect x="4" y="28" width="8" height="8" style="fill: #be5168"></rect><rect x="36" y="28" width="8" height="8" style="fill: #be5168"></rect><rect x="12" y="36" width="8" height="8" style="fill: #be5168"></rect><rect x="28" y="36" width="8" height="8" style="fill: #be5168"></rect><rect x="20" y="4" width="8" height="8" style="fill: #be5168"></rect><rect x="20" y="12" width="8" height="8" style="fill: #be5168"></rect><rect x="20" y="20" width="8" height="8" style="fill: #be5168"></rect></svg></div><div class="text-wrapper"><div role="meta" class="isso-comment-header"><span class="author">Wink Saville</span><span class="spacer">•</span><a href="#isso-242" class="permalink"><time title="Sun Dec 27 2015 16:39:24 GMT+0100 (Central European Standard Time)" datetime="2015-11-00T15:39:24Z">vor 3 Jahren</time></a><span class="note"></span></div><div class="text"><p>Philipp,</p><p>Just an FYI, In my <a href="https://github.com/winksaville/baremetal-x86_64">baremetal-x86_64</a> repo I ported your <a href="https://github.com/phil-opp/blog_os/blob/entering_longmode/src/arch/x86_64/boot.asm">boot.asm</a> to <a href="https://github.com/winksaville/baremetal-x86_64/blob/master/boot.gas.S">boot.gas.S</a> so I could use the code with gnu Assembler.</p></div><div class="isso-comment-footer"><span class="votes">0</span><a href="#" class="upvote"><!-- Generator: IcoMoon.io --><svg width="16" height="16" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" fill="gray">
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</a><a href="#" class="reply">Antworten</a></div><div class="isso-follow-up"></div></div></div></div></div></div><div id="isso-242" class="isso-comment isso-no-votes"><div class="avatar"><svg version="1.1" viewBox="0 0 48 48" preserveAspectRatio="xMinYMin meet" shape-rendering="crispEdges" data-hash="3773460ec1e4"><rect x="0" y="0" width="56" height="56" style="fill: #f0f0f0"></rect><rect x="4" y="4" width="8" height="8" style="fill: #be5168"></rect><rect x="36" y="4" width="8" height="8" style="fill: #be5168"></rect><rect x="4" y="20" width="8" height="8" style="fill: #be5168"></rect><rect x="36" y="20" width="8" height="8" style="fill: #be5168"></rect><rect x="4" y="28" width="8" height="8" style="fill: #be5168"></rect><rect x="36" y="28" width="8" height="8" style="fill: #be5168"></rect><rect x="12" y="36" width="8" height="8" style="fill: #be5168"></rect><rect x="28" y="36" width="8" height="8" style="fill: #be5168"></rect><rect x="20" y="4" width="8" height="8" style="fill: #be5168"></rect><rect x="20" y="12" width="8" height="8" style="fill: #be5168"></rect><rect x="20" y="20" width="8" height="8" style="fill: #be5168"></rect></svg></div><div class="text-wrapper"><div role="meta" class="isso-comment-header"><span class="author">Wink Saville</span><span class="spacer">•</span><a href="#isso-242" class="permalink"><time title="Sun Dec 27 2015 16:39:24 GMT+0100 (Central European Standard Time)" datetime="2015-11-00T15:39:24Z">vor 3 Jahren</time></a><span class="note"></span></div><div class="text"><p>Philipp,</p><p>Just an FYI, In my <a href="https://github.com/winksaville/baremetal-x86_64">baremetal-x86_64</a> repo I ported your boot.asm to boot.gas.S so I could use the code with gnu Assembler.</p></div><div class="isso-comment-footer"><span class="votes">0</span><a href="#" class="upvote"><!-- Generator: IcoMoon.io --><svg width="16" height="16" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" fill="gray">
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</a><a href="#" class="reply">Antworten</a></div><div class="isso-follow-up"><div id="isso-247" class="isso-comment isso-no-votes"><div class="avatar"><svg version="1.1" viewBox="0 0 48 48" preserveAspectRatio="xMinYMin meet" shape-rendering="crispEdges" data-hash="666df3217240"><rect x="0" y="0" width="56" height="56" style="fill: #f0f0f0"></rect><rect x="4" y="12" width="8" height="8" style="fill: #9abf88"></rect><rect x="36" y="12" width="8" height="8" style="fill: #9abf88"></rect><rect x="4" y="28" width="8" height="8" style="fill: #9abf88"></rect><rect x="36" y="28" width="8" height="8" style="fill: #9abf88"></rect><rect x="4" y="36" width="8" height="8" style="fill: #9abf88"></rect><rect x="36" y="36" width="8" height="8" style="fill: #9abf88"></rect><rect x="12" y="4" width="8" height="8" style="fill: #9abf88"></rect><rect x="28" y="4" width="8" height="8" style="fill: #9abf88"></rect><rect x="12" y="28" width="8" height="8" style="fill: #9abf88"></rect><rect x="28" y="28" width="8" height="8" style="fill: #9abf88"></rect><rect x="20" y="12" width="8" height="8" style="fill: #9abf88"></rect></svg></div><div class="text-wrapper"><div role="meta" class="isso-comment-header"><span class="author">Philipp Oppermann</span><span class="spacer">•</span><a href="#isso-247" class="permalink"><time title="Thu Feb 18 2016 17:57:38 GMT+0100 (Central European Standard Time)" datetime="2016-01-04T16:57:38Z">vor 3 Jahren</time></a><span class="note"></span></div><div class="text"><p>That was an interesting debugging session :D</p><p>I tried every debugging trick I knew, read the manual entries for all involved instructions, and even tried to use GDB. But I could not find the bug.</p><p>Then I gave up and just looked at the source code <a href="https://github.com/phil-opp/blog_os/tree/entering_longmode">in the repo</a> and created a diff to your code. And the problem was surprisingly simple:</p><p>You swapped `stack_bottom` and `stack_top`.</p><p>But this small change causes big problems. Every `push` or `call` instruction overwrites some bits of the `.text` section below. The last function in the source file and thus the last function in the `.text` section is `check_long_mode`. If you add something behind it, e.g. another error function, it is no longer overwritten and works again.</p><p>I think the counter-intuitive thing is that stuff further down in the source file ends up further up in memory. And the stack grows downwards to make it even more confusing. Maybe we should add a small note in the text, why `stack_bottom` needs to be _above_ `stack_top` in the file?</p></div><div class="isso-comment-footer"><span class="votes">0</span><a href="#" class="upvote"><!-- Generator: IcoMoon.io --><svg width="16" height="16" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" fill="gray">
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</a><a href="#" class="reply">Antworten</a></div><div class="isso-follow-up"><div id="isso-247" class="isso-comment isso-no-votes"><div class="avatar"><svg version="1.1" viewBox="0 0 48 48" preserveAspectRatio="xMinYMin meet" shape-rendering="crispEdges" data-hash="666df3217240"><rect x="0" y="0" width="56" height="56" style="fill: #f0f0f0"></rect><rect x="4" y="12" width="8" height="8" style="fill: #9abf88"></rect><rect x="36" y="12" width="8" height="8" style="fill: #9abf88"></rect><rect x="4" y="28" width="8" height="8" style="fill: #9abf88"></rect><rect x="36" y="28" width="8" height="8" style="fill: #9abf88"></rect><rect x="4" y="36" width="8" height="8" style="fill: #9abf88"></rect><rect x="36" y="36" width="8" height="8" style="fill: #9abf88"></rect><rect x="12" y="4" width="8" height="8" style="fill: #9abf88"></rect><rect x="28" y="4" width="8" height="8" style="fill: #9abf88"></rect><rect x="12" y="28" width="8" height="8" style="fill: #9abf88"></rect><rect x="28" y="28" width="8" height="8" style="fill: #9abf88"></rect><rect x="20" y="12" width="8" height="8" style="fill: #9abf88"></rect></svg></div><div class="text-wrapper"><div role="meta" class="isso-comment-header"><span class="author">Philipp Oppermann</span><span class="spacer">•</span><a href="#isso-247" class="permalink"><time title="Thu Feb 18 2016 17:57:38 GMT+0100 (Central European Standard Time)" datetime="2016-01-04T16:57:38Z">vor 3 Jahren</time></a><span class="note"></span></div><div class="text"><p>That was an interesting debugging session :D</p><p>I tried every debugging trick I knew, read the manual entries for all involved instructions, and even tried to use GDB. But I could not find the bug.</p><p>Then I gave up and just looked at the source code in the repo and created a diff to your code. And the problem was surprisingly simple:</p><p>You swapped `stack_bottom` and `stack_top`.</p><p>But this small change causes big problems. Every `push` or `call` instruction overwrites some bits of the `.text` section below. The last function in the source file and thus the last function in the `.text` section is `check_long_mode`. If you add something behind it, e.g. another error function, it is no longer overwritten and works again.</p><p>I think the counter-intuitive thing is that stuff further down in the source file ends up further up in memory. And the stack grows downwards to make it even more confusing. Maybe we should add a small note in the text, why `stack_bottom` needs to be _above_ `stack_top` in the file?</p></div><div class="isso-comment-footer"><span class="votes">0</span><a href="#" class="upvote"><!-- Generator: IcoMoon.io --><svg width="16" height="16" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" fill="gray">
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</a><a href="#" class="reply">Antworten</a></div><div class="isso-follow-up"></div></div></div><div id="isso-252" class="isso-comment isso-no-votes"><div class="avatar"><svg version="1.1" viewBox="0 0 48 48" preserveAspectRatio="xMinYMin meet" shape-rendering="crispEdges" data-hash="3773460ec1e4"><rect x="0" y="0" width="56" height="56" style="fill: #f0f0f0"></rect><rect x="4" y="4" width="8" height="8" style="fill: #be5168"></rect><rect x="36" y="4" width="8" height="8" style="fill: #be5168"></rect><rect x="4" y="20" width="8" height="8" style="fill: #be5168"></rect><rect x="36" y="20" width="8" height="8" style="fill: #be5168"></rect><rect x="4" y="28" width="8" height="8" style="fill: #be5168"></rect><rect x="36" y="28" width="8" height="8" style="fill: #be5168"></rect><rect x="12" y="36" width="8" height="8" style="fill: #be5168"></rect><rect x="28" y="36" width="8" height="8" style="fill: #be5168"></rect><rect x="20" y="4" width="8" height="8" style="fill: #be5168"></rect><rect x="20" y="12" width="8" height="8" style="fill: #be5168"></rect><rect x="20" y="20" width="8" height="8" style="fill: #be5168"></rect></svg></div><div class="text-wrapper"><div role="meta" class="isso-comment-header"><span class="author">Wink Saville</span><span class="spacer">•</span><a href="#isso-252" class="permalink"><time title="Tue Mar 01 2016 21:32:36 GMT+0100 (Central European Standard Time)" datetime="2016-02-02T20:32:36Z">vor 3 Jahren</time></a><span class="note"></span></div><div class="text"><p>Agreed, and I see that in my more sophisticated program, the question is what is it that I'm doing wrong. I believe I've setup the Interrupt Descriptor Table to handle all interrupts, i.e. I have an array of 256 interrupt gates. That program is here (<a href="https://github.com/winksaville/sadie)">https://github.com/winksavi...</a> but its too complicated to debug and I haven't yet checked in my non-working APIC timer code. But with that code I'm able to do software interrupts and also when my APIC timer code fires an interrupt fast enough it does work. So it would seem I've done most of the initialization "properly". Note, I'm also compiling my code with -mno-red-zone so that shouldn't be the problem.</p><p>So my debug strategy in situations such as this is to simplify. So the first thing was to just enable interrupts and doing nothing that should cause an interrupt to occur and then delay awhile in the code and see what happens. But, sure enough I'm still getting a double fault. Of course according to the documentation in the Intel SDM Volume 3 section 6.15 "Interrupt 8--Double Fault Exception (#DF)" the error code is 0 and CS EIP registers are undefined :(</p><p>Anyway, I then simplified to as simple as I can get. I modified your boot.asm program adding the code below the esp initialization that output's character to the VGA display.</p><p></p><pre><code><br>start:<br> mov esp, stack_top<br><br> ; Save registers<br> push edx<br> push ecx<br> push ebx<br> push eax<br><br> ; Enable interrupts<br> ;sti<br><br> ; Initialize edx to vga buffer ah attribute, al ch<br> mov edx, 0xb8000<br> mov ax, 0x0f60<br><br> ; ebx number of loops<br> mov ebx,10000<br><br>.loop:<br><br> ; Output next character and attribute<br> mov word [edx], ax<br><br> ; Increment to next character with wrap<br> inc al<br> cmp al, 0x7f<br> jne .nextloc<br> mov al,60<br><br> ; Next location with wrap<br>.nextloc:<br> add edx, 2<br> and edx,0x7ff<br> or edx,0xb8000<br><br> ; Delay<br> mov ecx,0x2000<br>.delay:<br> loop .delay<br><br> ; Continue looping until ebx is 0<br> dec ebx<br> jnz .loop<br><br> ; Disable interrupts<br> cli<br><br> ; Restore registers<br> pop eax<br> pop ebx<br> pop ecx<br> pop edx<br></code></pre><p></p><p>Here is a github repo: (<a href="https://github.com/winksaville/baremetal-po-x86_64/tree/test_enable_interrupts)">https://github.com/winksavi...</a>. If you add the above code to your boot.asm it will print 10,000 characters to the VGA display and then continue with the normal code paths. If the "sti" instruction is commented out, as it is above, then all is well. But if I uncomment the "sti" thus enabling interrupts then it fails.</p><p>I anticipated that enabling interrupts would succeed as I wouldn't expect any interrupts because the hardware is in a state where no interrupts should be generated. Or if grub or the BIOS is using interrupts then I'd expect things to also be OK.</p><p>Obviously I'm wrong and I'd hope you'd be able to suggest where my flaw is.</p></div><div class="isso-comment-footer"><span class="votes">0</span><a href="#" class="upvote"><!-- Generator: IcoMoon.io --><svg width="16" height="16" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" fill="gray">
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</a><a href="#" class="reply">Antworten</a></div><div class="isso-follow-up"></div></div></div><div id="isso-252" class="isso-comment isso-no-votes"><div class="avatar"><svg version="1.1" viewBox="0 0 48 48" preserveAspectRatio="xMinYMin meet" shape-rendering="crispEdges" data-hash="3773460ec1e4"><rect x="0" y="0" width="56" height="56" style="fill: #f0f0f0"></rect><rect x="4" y="4" width="8" height="8" style="fill: #be5168"></rect><rect x="36" y="4" width="8" height="8" style="fill: #be5168"></rect><rect x="4" y="20" width="8" height="8" style="fill: #be5168"></rect><rect x="36" y="20" width="8" height="8" style="fill: #be5168"></rect><rect x="4" y="28" width="8" height="8" style="fill: #be5168"></rect><rect x="36" y="28" width="8" height="8" style="fill: #be5168"></rect><rect x="12" y="36" width="8" height="8" style="fill: #be5168"></rect><rect x="28" y="36" width="8" height="8" style="fill: #be5168"></rect><rect x="20" y="4" width="8" height="8" style="fill: #be5168"></rect><rect x="20" y="12" width="8" height="8" style="fill: #be5168"></rect><rect x="20" y="20" width="8" height="8" style="fill: #be5168"></rect></svg></div><div class="text-wrapper"><div role="meta" class="isso-comment-header"><span class="author">Wink Saville</span><span class="spacer">•</span><a href="#isso-252" class="permalink"><time title="Tue Mar 01 2016 21:32:36 GMT+0100 (Central European Standard Time)" datetime="2016-02-02T20:32:36Z">vor 3 Jahren</time></a><span class="note"></span></div><div class="text"><p>Agreed, and I see that in my more sophisticated program, the question is what is it that I'm doing wrong. I believe I've setup the Interrupt Descriptor Table to handle all interrupts, i.e. I have an array of 256 interrupt gates. That program is here (https://github.com/winksaville/sadie but its too complicated to debug and I haven't yet checked in my non-working APIC timer code. But with that code I'm able to do software interrupts and also when my APIC timer code fires an interrupt fast enough it does work. So it would seem I've done most of the initialization "properly". Note, I'm also compiling my code with -mno-red-zone so that shouldn't be the problem.</p><p>So my debug strategy in situations such as this is to simplify. So the first thing was to just enable interrupts and doing nothing that should cause an interrupt to occur and then delay awhile in the code and see what happens. But, sure enough I'm still getting a double fault. Of course according to the documentation in the Intel SDM Volume 3 section 6.15 "Interrupt 8--Double Fault Exception (#DF)" the error code is 0 and CS EIP registers are undefined :(</p><p>Anyway, I then simplified to as simple as I can get. I modified your boot.asm program adding the code below the esp initialization that output's character to the VGA display.</p><p></p><pre><code><br>start:<br> mov esp, stack_top<br><br> ; Save registers<br> push edx<br> push ecx<br> push ebx<br> push eax<br><br> ; Enable interrupts<br> ;sti<br><br> ; Initialize edx to vga buffer ah attribute, al ch<br> mov edx, 0xb8000<br> mov ax, 0x0f60<br><br> ; ebx number of loops<br> mov ebx,10000<br><br>.loop:<br><br> ; Output next character and attribute<br> mov word [edx], ax<br><br> ; Increment to next character with wrap<br> inc al<br> cmp al, 0x7f<br> jne .nextloc<br> mov al,60<br><br> ; Next location with wrap<br>.nextloc:<br> add edx, 2<br> and edx,0x7ff<br> or edx,0xb8000<br><br> ; Delay<br> mov ecx,0x2000<br>.delay:<br> loop .delay<br><br> ; Continue looping until ebx is 0<br> dec ebx<br> jnz .loop<br><br> ; Disable interrupts<br> cli<br><br> ; Restore registers<br> pop eax<br> pop ebx<br> pop ecx<br> pop edx<br></code></pre><p></p><p>Here is a github repo: (https://github.com/winksaville/baremetal-po-x86_64/tree/test_enable_interrupts). If you add the above code to your boot.asm it will print 10,000 characters to the VGA display and then continue with the normal code paths. If the "sti" instruction is commented out, as it is above, then all is well. But if I uncomment the "sti" thus enabling interrupts then it fails.</p><p>I anticipated that enabling interrupts would succeed as I wouldn't expect any interrupts because the hardware is in a state where no interrupts should be generated. Or if grub or the BIOS is using interrupts then I'd expect things to also be OK.</p><p>Obviously I'm wrong and I'd hope you'd be able to suggest where my flaw is.</p></div><div class="isso-comment-footer"><span class="votes">0</span><a href="#" class="upvote"><!-- Generator: IcoMoon.io --><svg width="16" height="16" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" fill="gray">
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</a><a href="#" class="reply">Antworten</a></div><div class="isso-follow-up"></div></div></div><div id="isso-291" class="isso-comment isso-no-votes"><div class="avatar"><svg version="1.1" viewBox="0 0 48 48" preserveAspectRatio="xMinYMin meet" shape-rendering="crispEdges" data-hash="666df3217240"><rect x="0" y="0" width="56" height="56" style="fill: #f0f0f0"></rect><rect x="4" y="12" width="8" height="8" style="fill: #9abf88"></rect><rect x="36" y="12" width="8" height="8" style="fill: #9abf88"></rect><rect x="4" y="28" width="8" height="8" style="fill: #9abf88"></rect><rect x="36" y="28" width="8" height="8" style="fill: #9abf88"></rect><rect x="4" y="36" width="8" height="8" style="fill: #9abf88"></rect><rect x="36" y="36" width="8" height="8" style="fill: #9abf88"></rect><rect x="12" y="4" width="8" height="8" style="fill: #9abf88"></rect><rect x="28" y="4" width="8" height="8" style="fill: #9abf88"></rect><rect x="12" y="28" width="8" height="8" style="fill: #9abf88"></rect><rect x="28" y="28" width="8" height="8" style="fill: #9abf88"></rect><rect x="20" y="12" width="8" height="8" style="fill: #9abf88"></rect></svg></div><div class="text-wrapper"><div role="meta" class="isso-comment-header"><span class="author">Philipp Oppermann</span><span class="spacer">•</span><a href="#isso-291" class="permalink"><time title="Thu Jun 08 2017 11:44:20 GMT+0200 (Central European Summer Time)" datetime="2017-05-04T09:44:20Z">vor 2 Jahren</time></a><span class="note"></span></div><div class="text"><p>Hmm, do you have a link to the documentation? I can't find anything relevant on page 4-37 in this document: <a href="https://www.intel.com/Assets/en_US/PDF/manual/253667.pdf">https://www.intel.com/Asset...</a></p><p>The AMD64 manual (<a href="http://developer.amd.com/wordpress/media/2012/10/24593_APM_v21.pdf)">http://developer.amd.com/wo...</a> states on page 253:</p><p></p><blockquote>Normally, an IRET that pops a null selector into the SS register causes a general-protection exception (#GP) to occur. However, in long mode, the null selector indicates the existence of nested interrupt handlers and/or privileged software in 64-bit mode. Long mode allows an IRET to pop a null selector into SS from the stack under the following conditions:<br>• The target mode is 64-bit mode.<br>• The target CPL<3.<br>In this case, the processor does not load an SS descriptor, and the null selector is loaded into SS without causing a #GP exception<br></blockquote><p></p><p>Maybe I interpreted that wrong, though…</p></div><div class="isso-comment-footer"><span class="votes">0</span><a href="#" class="upvote"><!-- Generator: IcoMoon.io --><svg width="16" height="16" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" fill="gray">
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</a><a href="#" class="reply">Antworten</a></div><div class="isso-follow-up"></div></div></div><div id="isso-291" class="isso-comment isso-no-votes"><div class="avatar"><svg version="1.1" viewBox="0 0 48 48" preserveAspectRatio="xMinYMin meet" shape-rendering="crispEdges" data-hash="666df3217240"><rect x="0" y="0" width="56" height="56" style="fill: #f0f0f0"></rect><rect x="4" y="12" width="8" height="8" style="fill: #9abf88"></rect><rect x="36" y="12" width="8" height="8" style="fill: #9abf88"></rect><rect x="4" y="28" width="8" height="8" style="fill: #9abf88"></rect><rect x="36" y="28" width="8" height="8" style="fill: #9abf88"></rect><rect x="4" y="36" width="8" height="8" style="fill: #9abf88"></rect><rect x="36" y="36" width="8" height="8" style="fill: #9abf88"></rect><rect x="12" y="4" width="8" height="8" style="fill: #9abf88"></rect><rect x="28" y="4" width="8" height="8" style="fill: #9abf88"></rect><rect x="12" y="28" width="8" height="8" style="fill: #9abf88"></rect><rect x="28" y="28" width="8" height="8" style="fill: #9abf88"></rect><rect x="20" y="12" width="8" height="8" style="fill: #9abf88"></rect></svg></div><div class="text-wrapper"><div role="meta" class="isso-comment-header"><span class="author">Philipp Oppermann</span><span class="spacer">•</span><a href="#isso-291" class="permalink"><time title="Thu Jun 08 2017 11:44:20 GMT+0200 (Central European Summer Time)" datetime="2017-05-04T09:44:20Z">vor 2 Jahren</time></a><span class="note"></span></div><div class="text"><p>Hmm, do you have a link to the documentation? I can't find anything relevant on page 4-37 in this document: https://www.intel.com/Assets/en_US/PDF/manual/253667.pdf</p><p>The AMD64 manual states on page 253:</p><p></p><blockquote>Normally, an IRET that pops a null selector into the SS register causes a general-protection exception (#GP) to occur. However, in long mode, the null selector indicates the existence of nested interrupt handlers and/or privileged software in 64-bit mode. Long mode allows an IRET to pop a null selector into SS from the stack under the following conditions:<br>• The target mode is 64-bit mode.<br>• The target CPL<3.<br>In this case, the processor does not load an SS descriptor, and the null selector is loaded into SS without causing a #GP exception<br></blockquote><p></p><p>Maybe I interpreted that wrong, though…</p></div><div class="isso-comment-footer"><span class="votes">0</span><a href="#" class="upvote"><!-- Generator: IcoMoon.io --><svg width="16" height="16" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" fill="gray">
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</a><a href="#" class="reply">Antworten</a></div><div class="isso-follow-up"><div id="isso-306" class="isso-comment isso-no-votes"><div class="avatar"><svg version="1.1" viewBox="0 0 48 48" preserveAspectRatio="xMinYMin meet" shape-rendering="crispEdges" data-hash="5db23f819f9f"><rect x="0" y="0" width="56" height="56" style="fill: #f0f0f0"></rect><rect x="4" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="36" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="4" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="36" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="36" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="36" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="36" width="8" height="8" style="fill: #447c69"></rect></svg></div><div class="text-wrapper"><div role="meta" class="isso-comment-header"><a href="http://os.phil-opp.com" rel="nofollow" class="author">Philipp Oppermann</a><span class="spacer">•</span><a href="#isso-306" class="permalink"><time title="Sat Jul 08 2017 16:39:23 GMT+0200 (Central European Summer Time)" datetime="2017-06-06T14:39:23Z">letztes Jahr</time></a><span class="note"></span></div><div class="text"><p>You need to do a so-called far jump, which updates the code segment. I'm not sure right now if a far call is supported in long mode. Either way, returning to 32-bit code might not be a good idea anyway, since the opcodes might be interpreted differently.</p></div><div class="isso-comment-footer"><span class="votes">0</span><a href="#" class="upvote"><!-- Generator: IcoMoon.io --><svg width="16" height="16" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" fill="gray">
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</a><a href="#" class="reply">Antworten</a></div><div class="isso-follow-up"><div id="isso-306" class="isso-comment isso-no-votes"><div class="avatar"><svg version="1.1" viewBox="0 0 48 48" preserveAspectRatio="xMinYMin meet" shape-rendering="crispEdges" data-hash="5db23f819f9f"><rect x="0" y="0" width="56" height="56" style="fill: #f0f0f0"></rect><rect x="4" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="36" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="4" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="36" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="36" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="36" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="36" width="8" height="8" style="fill: #447c69"></rect></svg></div><div class="text-wrapper"><div role="meta" class="isso-comment-header">Philipp Oppermann<span class="spacer">•</span><a href="#isso-306" class="permalink"><time title="Sat Jul 08 2017 16:39:23 GMT+0200 (Central European Summer Time)" datetime="2017-06-06T14:39:23Z">letztes Jahr</time></a><span class="note"></span></div><div class="text"><p>You need to do a so-called far jump, which updates the code segment. I'm not sure right now if a far call is supported in long mode. Either way, returning to 32-bit code might not be a good idea anyway, since the opcodes might be interpreted differently.</p></div><div class="isso-comment-footer"><span class="votes">0</span><a href="#" class="upvote"><!-- Generator: IcoMoon.io --><svg width="16" height="16" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" fill="gray">
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<path d="M 24.773,18.299c-0.651-0.669-7.512-7.203-7.512-7.203C 16.912,10.739, 16.456,10.56, 16,10.56c-0.458,0-0.914,0.179-1.261,0.536 c0,0-6.861,6.534-7.514,7.203c-0.651,0.669-0.696,1.872,0,2.586c 0.698,0.712, 1.669,0.77, 2.522,0L 16,14.89l 6.251,5.995 c 0.854,0.77, 1.827,0.712, 2.522,0C 25.47,20.17, 25.427,18.966, 24.773,18.299z">
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</a><a href="#" class="reply">Antworten</a></div><div class="isso-follow-up"><div id="isso-308" class="isso-comment isso-no-votes"><div class="avatar"><svg version="1.1" viewBox="0 0 48 48" preserveAspectRatio="xMinYMin meet" shape-rendering="crispEdges" data-hash="5db23f819f9f"><rect x="0" y="0" width="56" height="56" style="fill: #f0f0f0"></rect><rect x="4" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="36" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="4" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="36" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="36" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="36" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="36" width="8" height="8" style="fill: #447c69"></rect></svg></div><div class="text-wrapper"><div role="meta" class="isso-comment-header"><a href="http://os.phil-opp.com" rel="nofollow" class="author">Philipp Oppermann</a><span class="spacer">•</span><a href="#isso-308" class="permalink"><time title="Wed Jul 12 2017 13:38:50 GMT+0200 (Central European Summer Time)" datetime="2017-06-03T11:38:50Z">letztes Jahr</time></a><span class="note"></span></div><div class="text"><p>Does the error occur when invoking nasm? Then you need to add <code>extern long_mode_start</code> somewhere inside the boot.asm (e.g. at the beginning). If it occurs while invoking ld, make sure that the <code>long_mode_init.asm</code> file is assembled and passed to ld (and it should of course define a global <code>long_mode_start:</code> label).</p></div><div class="isso-comment-footer"><span class="votes">0</span><a href="#" class="upvote"><!-- Generator: IcoMoon.io --><svg width="16" height="16" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" fill="gray">
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</a><a href="#" class="reply">Antworten</a></div><div class="isso-follow-up"><div id="isso-308" class="isso-comment isso-no-votes"><div class="avatar"><svg version="1.1" viewBox="0 0 48 48" preserveAspectRatio="xMinYMin meet" shape-rendering="crispEdges" data-hash="5db23f819f9f"><rect x="0" y="0" width="56" height="56" style="fill: #f0f0f0"></rect><rect x="4" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="36" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="4" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="36" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="36" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="36" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="36" width="8" height="8" style="fill: #447c69"></rect></svg></div><div class="text-wrapper"><div role="meta" class="isso-comment-header">Philipp Oppermann<span class="spacer">•</span><a href="#isso-308" class="permalink"><time title="Wed Jul 12 2017 13:38:50 GMT+0200 (Central European Summer Time)" datetime="2017-06-03T11:38:50Z">letztes Jahr</time></a><span class="note"></span></div><div class="text"><p>Does the error occur when invoking nasm? Then you need to add <code>extern long_mode_start</code> somewhere inside the boot.asm (e.g. at the beginning). If it occurs while invoking ld, make sure that the <code>long_mode_init.asm</code> file is assembled and passed to ld (and it should of course define a global <code>long_mode_start:</code> label).</p></div><div class="isso-comment-footer"><span class="votes">0</span><a href="#" class="upvote"><!-- Generator: IcoMoon.io --><svg width="16" height="16" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" fill="gray">
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</a><a href="#" class="reply">Antworten</a></div><div class="isso-follow-up"><div id="isso-312" class="isso-comment isso-no-votes"><div class="avatar"><svg version="1.1" viewBox="0 0 48 48" preserveAspectRatio="xMinYMin meet" shape-rendering="crispEdges" data-hash="5db23f819f9f"><rect x="0" y="0" width="56" height="56" style="fill: #f0f0f0"></rect><rect x="4" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="36" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="4" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="36" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="36" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="36" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="36" width="8" height="8" style="fill: #447c69"></rect></svg></div><div class="text-wrapper"><div role="meta" class="isso-comment-header"><a href="http://os.phil-opp.com" rel="nofollow" class="author">Philipp Oppermann</a><span class="spacer">•</span><a href="#isso-312" class="permalink"><time title="Sun Jul 16 2017 13:21:43 GMT+0200 (Central European Summer Time)" datetime="2017-06-00T11:21:43Z">letztes Jahr</time></a><span class="note"></span></div><div class="text"><p>Because the CR3 register can only be loaded from a register. So you have to load the <code>p4_table</code> address into a register first.</p></div><div class="isso-comment-footer"><span class="votes">0</span><a href="#" class="upvote"><!-- Generator: IcoMoon.io --><svg width="16" height="16" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" fill="gray">
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</a><a href="#" class="reply">Antworten</a></div><div class="isso-follow-up"><div id="isso-312" class="isso-comment isso-no-votes"><div class="avatar"><svg version="1.1" viewBox="0 0 48 48" preserveAspectRatio="xMinYMin meet" shape-rendering="crispEdges" data-hash="5db23f819f9f"><rect x="0" y="0" width="56" height="56" style="fill: #f0f0f0"></rect><rect x="4" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="36" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="4" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="36" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="12" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="20" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="12" y="36" width="8" height="8" style="fill: #447c69"></rect><rect x="28" y="36" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="4" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="28" width="8" height="8" style="fill: #447c69"></rect><rect x="20" y="36" width="8" height="8" style="fill: #447c69"></rect></svg></div><div class="text-wrapper"><div role="meta" class="isso-comment-header">Philipp Oppermann<span class="spacer">•</span><a href="#isso-312" class="permalink"><time title="Sun Jul 16 2017 13:21:43 GMT+0200 (Central European Summer Time)" datetime="2017-06-00T11:21:43Z">letztes Jahr</time></a><span class="note"></span></div><div class="text"><p>Because the CR3 register can only be loaded from a register. So you have to load the <code>p4_table</code> address into a register first.</p></div><div class="isso-comment-footer"><span class="votes">0</span><a href="#" class="upvote"><!-- Generator: IcoMoon.io --><svg width="16" height="16" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" fill="gray">
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<g>
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</path>
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@@ -714,8 +714,8 @@ hlt
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</svg>
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</a><a href="#" class="reply">Antworten</a></div><div class="isso-follow-up"></div></div></div><div id="isso-352" class="isso-comment"><div class="avatar"><svg version="1.1" viewBox="0 0 48 48" preserveAspectRatio="xMinYMin meet" shape-rendering="crispEdges" data-hash="58f409d0eeaa"><rect x="0" y="0" width="56" height="56" style="fill: #f0f0f0"></rect><rect x="4" y="20" width="8" height="8" style="fill: #e279a3"></rect><rect x="36" y="20" width="8" height="8" style="fill: #e279a3"></rect><rect x="4" y="28" width="8" height="8" style="fill: #e279a3"></rect><rect x="36" y="28" width="8" height="8" style="fill: #e279a3"></rect><rect x="4" y="36" width="8" height="8" style="fill: #e279a3"></rect><rect x="36" y="36" width="8" height="8" style="fill: #e279a3"></rect><rect x="12" y="12" width="8" height="8" style="fill: #e279a3"></rect><rect x="28" y="12" width="8" height="8" style="fill: #e279a3"></rect><rect x="12" y="20" width="8" height="8" style="fill: #e279a3"></rect><rect x="28" y="20" width="8" height="8" style="fill: #e279a3"></rect><rect x="12" y="28" width="8" height="8" style="fill: #e279a3"></rect><rect x="28" y="28" width="8" height="8" style="fill: #e279a3"></rect><rect x="20" y="4" width="8" height="8" style="fill: #e279a3"></rect><rect x="20" y="20" width="8" height="8" style="fill: #e279a3"></rect><rect x="20" y="36" width="8" height="8" style="fill: #e279a3"></rect></svg></div><div class="text-wrapper"><div role="meta" class="isso-comment-header"><span class="author">David</span><span class="spacer">•</span><a href="#isso-352" class="permalink"><time title="Thu Dec 14 2017 12:03:33 GMT+0100 (Central European Standard Time)" datetime="2017-11-04T11:03:33Z">letztes Jahr</time></a><span class="note"></span></div><div class="text"><p>I guess that what's unclear to me is why you say that each PTE entry
|
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contains the 52-bit physical address of the next frame/entry but in the
|
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</a><a href="#" class="reply">Antworten</a></div><div class="isso-follow-up"></div></div></div><div id="isso-352" class="isso-comment"><div class="avatar"><svg version="1.1" viewBox="0 0 48 48" preserveAspectRatio="xMinYMin meet" shape-rendering="crispEdges" data-hash="58f409d0eeaa"><rect x="0" y="0" width="56" height="56" style="fill: #f0f0f0"></rect><rect x="4" y="20" width="8" height="8" style="fill: #e279a3"></rect><rect x="36" y="20" width="8" height="8" style="fill: #e279a3"></rect><rect x="4" y="28" width="8" height="8" style="fill: #e279a3"></rect><rect x="36" y="28" width="8" height="8" style="fill: #e279a3"></rect><rect x="4" y="36" width="8" height="8" style="fill: #e279a3"></rect><rect x="36" y="36" width="8" height="8" style="fill: #e279a3"></rect><rect x="12" y="12" width="8" height="8" style="fill: #e279a3"></rect><rect x="28" y="12" width="8" height="8" style="fill: #e279a3"></rect><rect x="12" y="20" width="8" height="8" style="fill: #e279a3"></rect><rect x="28" y="20" width="8" height="8" style="fill: #e279a3"></rect><rect x="12" y="28" width="8" height="8" style="fill: #e279a3"></rect><rect x="28" y="28" width="8" height="8" style="fill: #e279a3"></rect><rect x="20" y="4" width="8" height="8" style="fill: #e279a3"></rect><rect x="20" y="20" width="8" height="8" style="fill: #e279a3"></rect><rect x="20" y="36" width="8" height="8" style="fill: #e279a3"></rect></svg></div><div class="text-wrapper"><div role="meta" class="isso-comment-header"><span class="author">David</span><span class="spacer">•</span><a href="#isso-352" class="permalink"><time title="Thu Dec 14 2017 12:03:33 GMT+0100 (Central European Standard Time)" datetime="2017-11-04T11:03:33Z">letztes Jahr</time></a><span class="note"></span></div><div class="text"><p>I guess that what's unclear to me is why you say that each PTE entry
|
||||
contains the 52-bit physical address of the next frame/entry but in the
|
||||
table it looks like only bits 12-51 (40 bits) are used for that.</p></div><div class="isso-comment-footer"><span class="votes">1</span><a href="#" class="upvote"><!-- Generator: IcoMoon.io --><svg width="16" height="16" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" fill="gray">
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<g>
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|
||||
|
||||
Reference in New Issue
Block a user