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<p>It had to be something more complicated because this demo program</p>
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<p></p>
<div><span style="font-family: "Courier New", monospace;">#include <stdio.h></span></div>
<div><span style="font-family: "Courier New", monospace;">#include <stdlib.h></span></div>
<div><br>
</div>
<div><span style="font-family: "Courier New", monospace;">struct one {</span></div>
<div><span class="Apple-tab-span" style="white-space: pre; font-family: "Courier New", monospace;"></span><span style="font-family: "Courier New", monospace;">char *foo;</span></div>
<div><span class="Apple-tab-span" style="white-space: pre; font-family: "Courier New", monospace;"></span><span style="font-family: "Courier New", monospace;">int bar[0];</span></div>
<div><span style="font-family: "Courier New", monospace;">};</span></div>
<div><br>
</div>
<div><span style="font-family: "Courier New", monospace;">struct two {</span></div>
<div><span class="Apple-tab-span" style="white-space: pre; font-family: "Courier New", monospace;"></span><span style="font-family: "Courier New", monospace;">char *foo;</span></div>
<div><span class="Apple-tab-span" style="white-space: pre; font-family: "Courier New", monospace;"></span><span style="font-family: "Courier New", monospace;">int bar[1];</span></div>
<div><span style="font-family: "Courier New", monospace;">};</span></div>
<div><br>
</div>
<div><span style="font-family: "Courier New", monospace;">int main(void)</span></div>
<div><span style="font-family: "Courier New", monospace;">{</span></div>
<div><span class="Apple-tab-span" style="white-space: pre; font-family: "Courier New", monospace;"></span><span style="font-family: "Courier New", monospace;">struct one *a = calloc(1, sizeof(struct one) + 4 * sizeof(int));</span></div>
<div><span class="Apple-tab-span" style="white-space: pre; font-family: "Courier New", monospace;"></span><span style="font-family: "Courier New", monospace;">struct two *b = calloc(1, sizeof(struct two) + 3 * sizeof(int));</span></div>
<div><span class="Apple-tab-span" style="white-space: pre; font-family: "Courier New", monospace;"></span><span style="font-family: "Courier New", monospace;">int x;</span></div>
<div><br>
</div>
<div><span class="Apple-tab-span" style="white-space: pre; font-family: "Courier New", monospace;"></span><span style="font-family: "Courier New", monospace;">printf("a == %p\n", a);</span></div>
<div><span class="Apple-tab-span" style="white-space: pre; font-family: "Courier New", monospace;"></span><span style="font-family: "Courier New", monospace;">for (x = 0; x < 4; x++)</span></div>
<div><span class="Apple-tab-span" style="white-space: pre; font-family: "Courier New", monospace;"></span><span style="font-family: "Courier New", monospace;">printf("&a.bar[%d] = %p\n", x, &a->bar[x]);</span></div>
<div><br>
</div>
<div><span class="Apple-tab-span" style="white-space: pre; font-family: "Courier New", monospace;"></span><span style="font-family: "Courier New", monospace;">printf("b == %p\n", b);</span></div>
<div><span class="Apple-tab-span" style="white-space: pre; font-family: "Courier New", monospace;"></span><span style="font-family: "Courier New", monospace;">for (x = 0; x < 4; x++)</span></div>
<div><span class="Apple-tab-span" style="white-space: pre; font-family: "Courier New", monospace;"></span><span style="font-family: "Courier New", monospace;">printf("&b.bar[%d] = %p\n", x, &b->bar[x]);</span></div>
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</div>
<div><span class="Apple-tab-span" style="white-space: pre; font-family: "Courier New", monospace;"></span><span style="font-family: "Courier New", monospace;">return 0;</span></div>
<div><span style="font-family: "Courier New", monospace;">}</span></div>
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<p></p>
<p>produces this output</p>
<p><br>
</p>
<p></p>
<div><span style="font-family: "Courier New", monospace;">tom@fx8:~$ gcc test.c -o test</span></div>
<div><span style="font-family: "Courier New", monospace;">tom@fx8:~$ ./test</span></div>
<div><span style="font-family: "Courier New", monospace;">a == 0x1fd4010</span></div>
<div><span style="font-family: "Courier New", monospace;">&a.bar[0] = 0x1fd4018</span></div>
<div><span style="font-family: "Courier New", monospace;">&a.bar[1] = 0x1fd401c</span></div>
<div><span style="font-family: "Courier New", monospace;">&a.bar[2] = 0x1fd4020</span></div>
<div><span style="font-family: "Courier New", monospace;">&a.bar[3] = 0x1fd4024</span></div>
<div><span style="font-family: "Courier New", monospace;">b == 0x1fd4030</span></div>
<div><span style="font-family: "Courier New", monospace;">&b.bar[0] = 0x1fd4038</span></div>
<div><span style="font-family: "Courier New", monospace;">&b.bar[1] = 0x1fd403c</span></div>
<div><span style="font-family: "Courier New", monospace;">&b.bar[2] = 0x1fd4040</span></div>
<div><span style="font-family: "Courier New", monospace;">&b.bar[3] = 0x1fd4044</span></div>
<div><br>
</div>
Which is exactly what you'd expect. I'm not strongly advocating we change the PP code just noting it's not really clear that it's correct from a first reading and in theory would be better with [0].
<p></p>
<div><br>
</div>
Tom<br>
<br>
<div style="color: rgb(0, 0, 0);">
<hr tabindex="-1" style="display:inline-block; width:98%">
<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Alex Deucher <alexdeucher@gmail.com><br>
<b>Sent:</b> Thursday, August 18, 2016 11:33<br>
<b>To:</b> StDenis, Tom<br>
<b>Cc:</b> Christian König; amd-gfx list<br>
<b>Subject:</b> Re: tidy'ing up cz_hwmgr.c</font>
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<div>The problem we ran into was when we had a struct like this:<br>
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struct table {<br>
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uint16_t size;<br>
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struct element elements[0];<br>
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<div>};<br>
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<div class="gmail_extra"><br>
</div>
<div class="gmail_extra">and then we would try and index the array:<br>
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<div class="gmail_extra">for (i = 0; i < table->size; i++) {<br>
</div>
<div class="gmail_extra"> element = &table->elements[i];<br>
</div>
<div class="gmail_extra">}<br>
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<div class="gmail_extra">element ended up off in the weeds. The only thing that seems to make some versions of gcc happy was pointer arithmetic. E.g.,<br>
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<div class="gmail_extra"><br>
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<div class="gmail_extra">element = (struct element *)((char *)&table->elements[0] + (sizeof(struct element) * i));<br>
<br>
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<div class="gmail_extra">Alex<br>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Thu, Aug 18, 2016 at 11:21 AM, StDenis, Tom <span dir="ltr">
<<a href="mailto:Tom.StDenis@amd.com" target="_blank">Tom.StDenis@amd.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex; border-left:1px #ccc solid; padding-left:1ex">
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<div style="font-size:12pt; color:#000000; background-color:#ffffff; font-family:Calibri,Arial,Helvetica,sans-serif">
<p>Any modern GCC should support [0] at the tail of a struct. This came up because when I was reading the code I saw they allocated 7 slots (plus the size of the struct) but then fill 8 slots. It's just weird
<img alt="😊" style="vertical-align: bottom; -webkit-user-select: none;" tabindex="0" src="cid:b9d342ca-4063-4b61-a23c-e54ecb4cfb09"></p>
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<p>Using [0] in the struct and allocating for 8 entries makes more sense and is clearer to read.</p>
<p><br>
</p>
<p>Tom</p>
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<div style="color:rgb(0,0,0)">
<hr style="display:inline-block; width:98%">
<div dir="ltr"><font color="#000000" face="Calibri, sans-serif" style="font-size:11pt"><b>From:</b> Christian König <<a href="mailto:deathsimple@vodafone.de" target="_blank">deathsimple@vodafone.de</a>><br>
<b>Sent:</b> Thursday, August 18, 2016 11:17<br>
<b>To:</b> StDenis, Tom; amd-gfx list<br>
<b>Subject:</b> Re: tidy'ing up cz_hwmgr.c</font>
<div> </div>
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<div class="h5">
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<blockquote type="cite">
<div>Has a [1] array at the tail which is then kzalloc'ed with N-1 entries. Shouldn't that just be a [0] with N entries allocated for clarity?</div>
</blockquote>
Actually the starting address of a dynamic array should be manually calculated instead of using [1] or [0].<br>
<br>
We had tons of problems with that because some gcc versions get this wrong and the atombios code used this as well.<br>
<br>
Alex how did we resolved such issues?<br>
<br>
Regards,<br>
Christian.<br>
<br>
Am 18.08.2016 um 16:26 schrieb StDenis, Tom:<br>
</div>
<blockquote type="cite">
<div style="font-size:12pt; color:#000000; background-color:#ffffff; font-family:Calibri,Arial,Helvetica,sans-serif">
<p>Tidying up cz_hwmgr.c I noted a couple of things but first is </p>
<p><br>
</p>
<div><span style="font-family:"Courier New",monospace">static bool cz_dpm_check_smu_features(<wbr>struct pp_hwmgr *hwmgr,</span></div>
<div><span style="white-space:pre-wrap; font-family:"Courier New",monospace"></span><span style="font-family:"Courier New",monospace">unsigned long check_feature);</span></div>
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<div>Which will return "true" if the smu call fails <b>or</b> the feature is set. </div>
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<div>The structure </div>
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<div>
<div><span style="font-family:"Courier New",monospace">struct phm_clock_voltage_dependency_<wbr>table;</span></div>
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<div>Has a [1] array at the tail which is then kzalloc'ed with N-1 entries. Shouldn't that just be a [0] with N entries allocated for clarity?</div>
<div><br>
</div>
<div>Tom</div>
<div><br>
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