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<a href="https://gitlab.rtems.org/sebhub">Sebastian Huber</a>
commented on a
discussion on <a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/1401#note_158712">bsps/mips/shared/irq/vectorexceptions.c</a>:
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<td class="new_line diff-line-num" data-linenumber="195" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
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<td class="line_content" style="padding: inherit;"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;"> <span class="line" data-lang="c"><span class="p">{</span></span>
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<td class="old_line diff-line-num old" data-linenumber="142" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #fac5cd; border-right-style: solid; padding: inherit;" align="right" bgcolor="#f9d7dc">
142
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<td class="new_line diff-line-num old" data-linenumber="196" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #fac5cd; border-right-style: solid; padding: inherit;" align="right" bgcolor="#f9d7dc">
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<td class="line_content old" style="padding: inherit;" bgcolor="#fbe9eb"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;">-<span class="line" data-lang="c"> <span class="p">(</span><span class="kt" style="color: #445588; font-weight: 600;">void</span><span class="p">)</span> <span class="n" style="color: #333333;">frame</span><span class="p">;</span></span>
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<td class="old_line diff-line-num old" data-linenumber="143" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #fac5cd; border-right-style: solid; padding: inherit;" align="right" bgcolor="#f9d7dc">
143
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<td class="new_line diff-line-num old" data-linenumber="196" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #fac5cd; border-right-style: solid; padding: inherit;" align="right" bgcolor="#f9d7dc">
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<td class="line_content old" style="padding: inherit;" bgcolor="#fbe9eb"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;">-<span class="line" data-lang="c"></span>
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<td class="old_line diff-line-num" data-linenumber="144" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
144
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<td class="new_line diff-line-num" data-linenumber="196" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
196
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<td class="line_content" style="padding: inherit;"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;"> <span class="line" data-lang="c"> <span class="kt" style="color: #445588; font-weight: 600;">uint32_t</span> <span class="n" style="color: #333333;">cause</span><span class="p">;</span></span>
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<td class="old_line diff-line-num" data-linenumber="145" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
145
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<td class="new_line diff-line-num" data-linenumber="197" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
197
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<td class="line_content" style="padding: inherit;"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;"> <span class="line" data-lang="c"> <span class="kt" style="color: #445588; font-weight: 600;">uint32_t</span> <span class="n" style="color: #333333;">exc</span><span class="p">;</span></span>
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<td class="old_line diff-line-num" data-linenumber="146" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
146
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<td class="new_line diff-line-num" data-linenumber="198" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
198
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<td class="line_content" style="padding: inherit;"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;"> <span class="line" data-lang="c"></span>
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<td class="old_line diff-line-num" data-linenumber="147" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
147
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<td class="new_line diff-line-num" data-linenumber="199" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
199
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<td class="line_content" style="padding: inherit;"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;"> <span class="line" data-lang="c"> <span class="n" style="color: #333333;">mips_get_cause</span><span class="p">(</span> <span class="n" style="color: #333333;">cause</span> <span class="p">);</span></span>
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<td class="old_line diff-line-num" data-linenumber="148" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
148
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<td class="new_line diff-line-num" data-linenumber="200" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
200
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<td class="line_content" style="padding: inherit;"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;"> <span class="line" data-lang="c"> <span class="n" style="color: #333333;">exc</span> <span class="o" style="font-weight: 600;">=</span> <span class="p">(</span><span class="n" style="color: #333333;">cause</span> <span class="o" style="font-weight: 600;">>></span> <span class="mi" style="color: #009999;">2</span><span class="p">)</span> <span class="o" style="font-weight: 600;">&</span> <span class="mh" style="color: #009999;">0x1f</span><span class="p">;</span></span>
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149
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<td class="new_line diff-line-num" data-linenumber="201" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
201
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<td class="line_content" style="padding: inherit;"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;"> <span class="line" data-lang="c"></span>
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<td class="new_line diff-line-num new" data-linenumber="202" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
202
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;">+<span class="line" data-lang="c"> <span class="k" style="font-weight: 600;">if</span> <span class="p">(</span> <span class="n" style="color: #333333;">exc</span> <span class="o" style="font-weight: 600;">==</span> <span class="n" style="color: #333333;">MIPS_EXCEPTION_RI</span> <span class="o" style="font-weight: 600;">&&</span> <span class="n" style="color: #333333;">mips_emulate_rdhwr_ulr</span><span class="p">(</span> <span class="n" style="color: #333333;">frame</span> <span class="p">)</span> <span class="p">)</span> <span class="p">{</span></span>
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203
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;">+<span class="line" data-lang="c"> <span class="k" style="font-weight: 600;">return</span><span class="p">;</span></span>
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<td class="new_line diff-line-num new" data-linenumber="204" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
204
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;">+<span class="line" data-lang="c"> <span class="p">}</span></span>
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<td class="new_line diff-line-num new" data-linenumber="205" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
205
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;">+<span class="line" data-lang="c"></span>
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<td class="old_line diff-line-num" data-linenumber="150" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
150
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<td class="new_line diff-line-num" data-linenumber="206" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
206
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<td class="line_content" style="padding: inherit;"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;"> <span class="line" data-lang="c"> <span class="n" style="color: #333333;">mips_exception_frame</span> <span class="o" style="font-weight: 600;">=</span> <span class="n" style="color: #333333;">frame</span><span class="p">;</span></span>
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<td class="old_line diff-line-num" data-linenumber="151" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
151
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<td class="new_line diff-line-num" data-linenumber="207" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
207
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<td class="line_content" style="padding: inherit;"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;"> <span class="line" data-lang="c"> <span class="n" style="color: #333333;">bsp_interrupt_handler_dispatch</span><span class="p">(</span> <span class="n" style="color: #333333;">exc</span> <span class="p">);</span></span>
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<td class="old_line diff-line-num" data-linenumber="152" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
152
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<td class="new_line diff-line-num" data-linenumber="208" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
208
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<td class="line_content" style="padding: inherit;"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;"> <span class="line" data-lang="c"> <span class="n" style="color: #333333;">mips_exception_frame</span> <span class="o" style="font-weight: 600;">=</span> <span class="nb" style="color: #0086b3;">NULL</span><span class="p">;</span></span>
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<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">I filed three issues for this:</p>
<ul dir="auto" style="text-align: initial; list-style-type: disc; margin: 0px 0px 1rem; padding: 0;">
<li style="margin-top: 0px; line-height: 1.6em; margin-left: 25px; padding-left: 3px;">
<a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5752" title="bsps/mips: The exception vector publishes the frame in a global" class="gfm gfm-issue" data-original="#5752" data-link="false" data-link-reference="false" data-issue="29983" data-project="26" data-iid="5752" data-namespace-path="rtems/rtos/rtems" data-project-path="rtems/rtos/rtems" data-issue-type="issue" data-container="body" data-placement="top" data-reference-type="issue" style="margin-top: 0px;">#5752</a> for the <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; white-space: pre-wrap; overflow-wrap: break-word; word-break: keep-all; padding: 0.125rem 0.25rem;">mips_exception_frame</code> global</li>
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<a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5753" title="bsps/mips: The compiler emits rdhwr for a processor which lacks it" class="gfm gfm-issue" data-original="#5753" data-link="false" data-link-reference="false" data-issue="29984" data-project="26" data-iid="5753" data-namespace-path="rtems/rtos/rtems" data-project-path="rtems/rtos/rtems" data-issue-type="issue" data-container="body" data-placement="top" data-reference-type="issue" style="margin-top: 0px;">#5753</a> for the thread pointer and <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; white-space: pre-wrap; overflow-wrap: break-word; word-break: keep-all; padding: 0.125rem 0.25rem;">rdhwr</code>
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<a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5754" title="score: Most ports cannot resume from an exception frame" class="gfm gfm-issue" data-original="#5754" data-link="false" data-link-reference="false" data-issue="29985" data-project="26" data-iid="5754" data-namespace-path="rtems/rtos/rtems" data-project-path="rtems/rtos/rtems" data-issue-type="issue" data-container="body" data-placement="top" data-reference-type="issue" style="margin-top: 0px;">#5754</a> for <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; white-space: pre-wrap; overflow-wrap: break-word; word-break: keep-all; padding: 0.125rem 0.25rem;">_CPU_Exception_resume()</code> across all ports</li>
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<h3 dir="auto" style="margin-top: 1.5rem; margin-bottom: 1rem; font-weight: 600; font-size: 1.125rem; letter-spacing: inherit; line-height: 1.25; color: #18171d;" align="initial">
<a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5752" title="bsps/mips: The exception vector publishes the frame in a global" class="gfm gfm-issue" data-original="#5752" data-link="false" data-link-reference="false" data-issue="29983" data-project="26" data-iid="5752" data-namespace-path="rtems/rtos/rtems" data-project-path="rtems/rtos/rtems" data-issue-type="issue" data-container="body" data-placement="top" data-reference-type="issue" style="margin-top: 0px;">#5752</a>, the global</h3>
<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">Agreed, and it is older than this merge request. It came in with <a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/commit/7ec23f42d6111d98226f1325ba81939efca402bc" title="bsps/mips: Report an exception as one" class="gfm gfm-commit has-tooltip" data-original="7ec23f42d61" data-link="false" data-link-reference="false" data-commit="7ec23f42d6111d98226f1325ba81939efca402bc" data-project="26" data-container="body" data-placement="top" data-reference-type="commit" style="font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; font-size: 95%; margin-top: 0px;">7ec23f42</a>.
The exception vectors are dispatched through the interrupt manager because
<code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">mips_gdb_stub_install()</code> installs a handler on 18 of them, so the frame had
to reach <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">bsp_interrupt_handler_default()</code> somehow.</p>
<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">The fix is to give the MIPS port its own exception handler registration in the
shape of <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0px; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">ppc_exc_set_handler()</code>, where a handler takes a
<code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">CPU_Exception_frame *</code>. The GDB stub moves to it, and the default handler
calls <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">rtems_fatal()</code> with <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">RTEMS_FATAL_SOURCE_EXCEPTION</code> and the frame, like
<code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">C_exception_handler()</code> does on PowerPC. That changes the existing exception
API of the MIPS port, which is why it is a separate issue.</p>
<h3 dir="auto" style="margin-top: 1.5rem; margin-bottom: 1rem; font-weight: 600; font-size: 1.125rem; letter-spacing: inherit; line-height: 1.25; color: #18171d;" align="initial">
<a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5753" title="bsps/mips: The compiler emits rdhwr for a processor which lacks it" class="gfm gfm-issue" data-original="#5753" data-link="false" data-link-reference="false" data-issue="29984" data-project="26" data-iid="5753" data-namespace-path="rtems/rtos/rtems" data-project-path="rtems/rtos/rtems" data-issue-type="issue" data-container="body" data-placement="top" data-reference-type="issue" style="margin-top: 0px;">#5753</a>, the TLS model</h3>
<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">I measured this before answering. In an RTEMS configuration the compiler emits
<code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0px; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">rdhwr</code> whatever the TLS model:</p>
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<pre data-canonical-lang="c" class="code highlight js-syntax-highlight language-c" v-pre="true" style="display: block; font-size: 90%; color: #3a383f; line-height: 1.6em; overflow-x: auto; border-radius: .25rem; position: relative; font-family: monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: #ffffff; -premailer-cellpadding: 0; -premailer-cellspacing: 0; -premailer-width: 100%; margin: 0px 0 1rem; padding: 12px; border: 1px solid #dcdcde;"><code style="font-size: inherit; color: inherit; word-wrap: normal; word-break: keep-all; background-color: inherit; border-radius: .25rem; white-space: pre; margin-top: 0px; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; overflow-wrap: normal; padding: unset;"><span id="LC1" class="line" lang="c" style="margin-top: 0px;"><span class="k" style="margin-top: 0px; font-weight: 600;">extern</span> <span class="kr" style="font-weight: 600;">__thread</span> <span class="kt" style="color: #445588; font-weight: 600;">int</span> <span class="n" style="color: #333333;">y</span><span class="p">;</span></span>
<span id="LC2" class="line" lang="c"><span class="kt" style="margin-top: 0px; color: #445588; font-weight: 600;">int</span> <span class="nf" style="color: #990000; font-weight: 600;">get2</span><span class="p">(</span><span class="kt" style="color: #445588; font-weight: 600;">void</span><span class="p">)</span> <span class="p">{</span> <span class="k" style="font-weight: 600;">return</span> <span class="n" style="color: #333333;">y</span><span class="p">;</span> <span class="p">}</span></span></code></pre>
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<pre class="code highlight js-syntax-highlight language-plaintext" v-pre="true" style="display: block; font-size: 90%; color: #3a383f; line-height: 1.6em; overflow-x: auto; border-radius: .25rem; position: relative; font-family: monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: #ffffff; -premailer-cellpadding: 0; -premailer-cellspacing: 0; -premailer-width: 100%; margin: 0px 0 1rem; padding: 12px; border: 1px solid #dcdcde;"><code style="font-size: inherit; color: inherit; word-wrap: normal; word-break: keep-all; background-color: inherit; border-radius: .25rem; white-space: pre; margin-top: 0px; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; overflow-wrap: normal; padding: unset;"><span id="LC1" class="line" lang="plaintext" style="margin-top: 0px;">$ mips-rtems7-gcc -O2 -S -march=r3900 -ftls-model=global-dynamic tls.c</span>
<span id="LC2" class="line" lang="plaintext">get2:</span>
<span id="LC3" class="line" lang="plaintext"> .set push</span>
<span id="LC4" class="line" lang="plaintext"> .set mips32r2</span>
<span id="LC5" class="line" lang="plaintext"> rdhwr $3,$29</span>
<span id="LC6" class="line" lang="plaintext"> .set pop</span>
<span id="LC7" class="line" lang="plaintext"> lui $2,%tprel_hi(y)</span>
<span id="LC8" class="line" lang="plaintext"> addu $2,$2,$3</span>
<span id="LC9" class="line" lang="plaintext"> jr $31</span></code></pre>
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<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">All five values of -ftls-model give that. Note the .set mips32r2 around the
rdhwr under -march=r3900: the backend emits an instruction the selected
processor cannot execute.</p>
<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">__tls_get_addr() does appear, but only here:</p>
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<pre class="code highlight js-syntax-highlight language-plaintext" v-pre="true" style="display: block; font-size: 90%; color: #3a383f; line-height: 1.6em; overflow-x: auto; border-radius: .25rem; position: relative; font-family: monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: #ffffff; -premailer-cellpadding: 0; -premailer-cellspacing: 0; -premailer-width: 100%; margin: 0px 0 1rem; padding: 12px; border: 1px solid #dcdcde;"><code style="font-size: inherit; color: inherit; word-wrap: normal; word-break: keep-all; background-color: inherit; border-radius: .25rem; white-space: pre; margin-top: 0px; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; overflow-wrap: normal; padding: unset;"><span id="LC1" class="line" lang="plaintext" style="margin-top: 0px;">$ mips-rtems7-gcc -O2 -S -march=r3900 -fpic -mabicalls -mshared \</span>
<span id="LC2" class="line" lang="plaintext"> -ftls-model=global-dynamic tls.c</span>
<span id="LC3" class="line" lang="plaintext"> lw $25,%call16(__tls_get_addr)($28)</span>
<span id="LC4" class="line" lang="plaintext"> addiu $4,$28,%tlsgd(y)</span></code></pre>
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<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">-mabicalls is disabled by default for mips-rtems7, and enabling it moves
the BSPs to the GOT based PIC ABI. On top of that the linker relaxes a general
dynamic sequence to local exec in a static link, which puts rdhwr back.</p>
<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">So a compiler change is needed either way, and the smaller one is the one ARM
already has. -mtp=soft makes GCC emit a call of __aeabi_read_tp(), and we
supply that function in cpukit/score/cpu/arm/__aeabi_read_tp.c. <a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5753" title="bsps/mips: The compiler emits rdhwr for a processor which lacks it" class="gfm gfm-issue" data-original="#5753" data-link="false" data-link-reference="false" data-issue="29984" data-project="26" data-iid="5753" data-namespace-path="rtems/rtos/rtems" data-project-path="rtems/rtos/rtems" data-issue-type="issue" data-container="body" data-placement="top" data-reference-type="issue" style="margin-top: 0px;">#5753</a> asks
for the same option in the MIPS backend, the matching helper under
cpukit/score/cpu/mips/, and the flag in ABI_FLAGS so application objects
carry it too. mips_emulate_rdhwr_ulr() and the reserved instruction case in
mips_vector_exceptions() then go away.</p>
<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">Until such a compiler exists, the emulation is what makes thread-local storage
work on the R3900, so I would like to keep it here and remove it in <a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5753" title="bsps/mips: The compiler emits rdhwr for a processor which lacks it" class="gfm gfm-issue" data-original="#5753" data-link="false" data-link-reference="false" data-issue="29984" data-project="26" data-iid="5753" data-namespace-path="rtems/rtos/rtems" data-project-path="rtems/rtos/rtems" data-issue-type="issue" data-container="body" data-placement="top" data-reference-type="issue" style="margin-top: 0px;">#5753</a>.</p>
<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial"><a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5754" title="score: Most ports cannot resume from an exception frame" class="gfm gfm-issue" data-original="#5754" data-link="false" data-link-reference="false" data-issue="29985" data-project="26" data-iid="5754" data-namespace-path="rtems/rtos/rtems" data-project-path="rtems/rtos/rtems" data-issue-type="issue" data-container="body" data-placement="top" data-reference-type="issue" style="margin-top: 0px;">#5754</a>, exception extensions</p>
<p dir="auto" style="color: #3a383f; margin: 0px;" align="initial">Your first comment pointed at these. _CPU_Exception_resume() exists in three
ports, with two signatures and two headers, and RTEMS_EXCEPTION_EXTENSIONS is
enabled for aarch64 and microblaze only, although arm builds its
implementation with the option off. <a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5754" title="score: Most ports cannot resume from an exception frame" class="gfm gfm-issue" data-original="#5754" data-link="false" data-link-reference="false" data-issue="29985" data-project="26" data-iid="5754" data-namespace-path="rtems/rtos/rtems" data-project-path="rtems/rtos/rtems" data-issue-type="issue" data-container="body" data-placement="top" data-reference-type="issue" style="margin-top: 0px;">#5754</a> proposes one declaration in
cpuimpl.h, mandatory for every port, with validation tests driven from the
ISA and ABI reference documents.</p>
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