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<h3>
Ben Gamari pushed to branch wip/bss-alignment
at <a href="https://gitlab.haskell.org/ghc/ghc">Glasgow Haskell Compiler / GHC</a>
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<h4>
Commits:
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<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/0ab1a308139e73070b23b156a83eb094a97ba0ec">0ab1a308</a></strong>
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<span>by Ben Gamari</span>
<i>at 2020-11-18T11:42:43-05:00</i>
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<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">rts/linker: Align bssSize to page size when mapping symbol extras
We place symbol_extras right after bss. We also need
to ensure that symbol_extras can be mprotect'd independently from the
rest of the image. To ensure this we round up the size of bss to a page
boundary, thus ensuring that symbol_extras is also page-aligned.
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<h4>1 changed file:</h4>
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<a href="#4f7a8996954df0bb6d580c202be08ec03af67514">
rts/linker/SymbolExtras.c
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<h4>Changes:</h4>
<li id="4f7a8996954df0bb6d580c202be08ec03af67514">
<a href="https://gitlab.haskell.org/ghc/ghc/-/commit/0ab1a308139e73070b23b156a83eb094a97ba0ec#4f7a8996954df0bb6d580c202be08ec03af67514"><strong>rts/linker/SymbolExtras.c</strong></a>
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<td class="line_content match " style="padding-left: 0.5em; padding-right: 0.5em; color: rgba(0,0,0,0.3);" bgcolor="#fafafa">@@ -77,7 +77,9 @@ int ocAllocateExtras(ObjectCode* oc, int count, int first, int bssSize)</td>
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<pre style="margin: 0;"> <span id="LC77" class="line" lang="c"> <span class="cm" style="color: #998; font-style: italic;">/* N.B. We currently can't mark symbol extras as non-executable in this</span></span>
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<pre style="margin: 0;"> <span id="LC78" class="line" lang="c"><span class="cm" style="color: #998; font-style: italic;"> * case. */</span></span>
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<pre style="margin: 0;"> <span id="LC79" class="line" lang="c"> <span class="kt" style="color: #458; font-weight: 600;">size_t</span> <span class="n" style="color: #333;">n</span> <span class="o" style="font-weight: 600;">=</span> <span class="n" style="color: #333;">roundUpToPage</span><span class="p">(</span><span class="n" style="color: #333;">oc</span><span class="o" style="font-weight: 600;">-></span><span class="n" style="color: #333;">fileSize</span><span class="p">);</span></span>
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<pre style="margin: 0;">-<span id="LC80" class="line" lang="c"> <span class="n" style="color: #333;">bssSize</span> <span class="o" style="font-weight: 600;">=</span> <span class="n" style="color: #333;">roundUpToAlign</span><span class="p">(</span><span class="n" style="color: #333;">bssSize</span><span class="p">,</span> <span class="mi" style="color: #099;">8</span><span class="p">);</span></span>
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<pre style="margin: 0;">+<span id="LC80" class="line" lang="c"> <span class="c1" style="color: #998; font-style: italic;">// round bssSize up to the nearest page size since we need to ensure that</span></span>
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<pre style="margin: 0;">+<span id="LC81" class="line" lang="c"> <span class="c1" style="color: #998; font-style: italic;">// symbol_extras is aligned to a page boundary so it can be mprotect'd.</span></span>
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<pre style="margin: 0;">+<span id="LC82" class="line" lang="c"> <span class="n" style="color: #333;">bssSize</span> <span class="o" style="font-weight: 600;">=</span> <span class="n" style="color: #333;">roundUpToPage</span><span class="p">(</span><span class="n" style="color: #333;">bssSize</span><span class="p">);</span></span>
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<pre style="margin: 0;"> <span id="LC83" class="line" lang="c"> <span class="kt" style="color: #458; font-weight: 600;">size_t</span> <span class="n" style="color: #333;">allocated_size</span> <span class="o" style="font-weight: 600;">=</span> <span class="n" style="color: #333;">n</span> <span class="o" style="font-weight: 600;">+</span> <span class="n" style="color: #333;">bssSize</span> <span class="o" style="font-weight: 600;">+</span> <span class="n" style="color: #333;">extras_size</span><span class="p">;</span></span>
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<pre style="margin: 0;"> <span id="LC84" class="line" lang="c"> <span class="kt" style="color: #458; font-weight: 600;">void</span> <span class="o" style="font-weight: 600;">*</span><span class="n" style="color: #333;">new</span> <span class="o" style="font-weight: 600;">=</span> <span class="n" style="color: #333;">mmapForLinker</span><span class="p">(</span><span class="n" style="color: #333;">allocated_size</span><span class="p">,</span> <span class="n" style="color: #333;">PROT_READ</span> <span class="o" style="font-weight: 600;">|</span> <span class="n" style="color: #333;">PROT_WRITE</span><span class="p">,</span> <span class="n" style="color: #333;">MAP_ANONYMOUS</span><span class="p">,</span> <span class="o" style="font-weight: 600;">-</span><span class="mi" style="color: #099;">1</span><span class="p">,</span> <span class="mi" style="color: #099;">0</span><span class="p">);</span></span>
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<pre style="margin: 0;"> <span id="LC85" class="line" lang="c"> <span class="k" style="font-weight: 600;">if</span> <span class="p">(</span><span class="n" style="color: #333;">new</span><span class="p">)</span> <span class="p">{</span></span>
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