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<a href="https://gitlab.com/nmav">Nikos Mavrogiannopoulos</a>
commented on a discussion
on <a href="https://gitlab.com/gnutls/gnutls/commit/d087db43e07c9b9df115ae9467bede5fa796c302#note_93287236">lib/safe-memfuncs.c</a>:
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<pre style="margin: 0;"> <span id="LC30" class="line" lang="c"><span class="cm" style="color: #998; font-style: italic;"> * This function will operate similarly to memset(), but will</span></span>
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<pre style="margin: 0;"> <span id="LC31" class="line" lang="c"><span class="cm" style="color: #998; font-style: italic;"> * not be optimized out by the compiler.</span></span>
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<pre style="margin: 0;"> <span id="LC32" class="line" lang="c"><span class="cm" style="color: #998; font-style: italic;"> *</span></span>
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<pre style="margin: 0;">-<span id="LC36" class="line" lang="c"><span class="cm" style="color: #998; font-style: italic;"> * Returns: void.</span></span>
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<pre style="margin: 0;">-<span id="LC37" class="line" lang="c"><span class="cm" style="color: #998; font-style: italic;"> *</span></span>
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<pre style="margin: 0;"> <span id="LC33" class="line" lang="c"><span class="cm" style="color: #998; font-style: italic;"> * Since: 3.4.0</span></span>
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<pre style="margin: 0;"> <span id="LC34" class="line" lang="c"><span class="cm" style="color: #998; font-style: italic;"> **/</span></span>
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<pre style="margin: 0;"> <span id="LC35" class="line" lang="c"><span class="kt" style="color: #458; font-weight: 600;">void</span> <span class="nf" style="color: #900; font-weight: 600;">gnutls_memset</span><span class="p">(</span><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;">data</span><span class="p">,</span> <span class="kt" style="color: #458; font-weight: 600;">int</span> <span class="n" style="color: #333;">c</span><span class="p">,</span> <span class="kt" style="color: #458; font-weight: 600;">size_t</span> <span class="n" style="color: #333;">size</span><span class="p">)</span></span>
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<pre style="margin: 0;"> <span id="LC36" class="line" lang="c"><span class="p">{</span></span>
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<pre style="margin: 0;">-<span id="LC42" class="line" lang="c"> <span class="k" style="font-weight: 600;">volatile</span> <span class="kt" style="color: #458; font-weight: 600;">unsigned</span> <span class="n" style="color: #333;">volatile_zero</span><span class="idiff left"> </span><span class="o" style="font-weight: 600;"><span class="idiff">=</span></span><span class="idiff"> </span><span class="mi" style="color: #099;"><span class="idiff right">0</span></span><span class="p">;</span></span>
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<pre style="margin: 0;">+<span id="LC37" class="line" lang="c"> <span class="k" style="font-weight: 600;">volatile</span> <span class="kt" style="color: #458; font-weight: 600;">unsigned</span> <span class="n" style="color: #333;">volatile_zero</span><span class="p">;</span></span>
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<pre style="margin: 0;"> <span id="LC38" class="line" lang="c"> <span class="k" style="font-weight: 600;">volatile</span> <span class="kt" style="color: #458; font-weight: 600;">char</span> <span class="o" style="font-weight: 600;">*</span><span class="n" style="color: #333;">vdata</span> <span class="o" style="font-weight: 600;">=</span> <span class="p">(</span><span class="k" style="font-weight: 600;">volatile</span> <span class="kt" style="color: #458; font-weight: 600;">char</span><span class="o" style="font-weight: 600;">*</span><span class="p">)</span><span class="n" style="color: #333;">data</span><span class="p">;</span></span>
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<pre style="margin: 0;">+<span id="LC39" class="line" lang="c"><span class="cp" style="color: #999; font-weight: 600;">#ifdef HAVE_EXPLICIT_BZERO</span></span>
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<pre style="margin: 0;">+<span id="LC40" class="line" lang="c"> <span class="k" style="font-weight: 600;">if</span> <span class="p">(</span><span class="n" style="color: #333;">c</span> <span class="o" style="font-weight: 600;">==</span> <span class="mi" style="color: #099;">0</span><span class="p">)</span> <span class="p">{</span></span>
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<pre style="margin: 0;">+<span id="LC41" class="line" lang="c"> <span class="n" style="color: #333;">explicit_bzero</span><span class="p">(</span><span class="n" style="color: #333;">data</span><span class="p">,</span> <span class="n" style="color: #333;">size</span><span class="p">);</span></span>
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<p dir="auto">According to manpage:</p>
<pre class="code highlight js-syntax-highlight plaintext" lang="plaintext" v-pre="true" style="background-color: #fff; font-family: monospace; font-size: 90%; -premailer-cellpadding: 0; -premailer-cellspacing: 0; -premailer-width: 100%; margin: 0;"><code><span id="LC1" class="line" lang="plaintext">It differs from bzero() in that it guarantees that compiler optimizations will not remove the erase operation if the compiler deduces that the operation is "unnecessary".</span></code></pre>
<p dir="auto">Implementation wise it adds a barrier after memset().
<a href="https://code.woboq.org/userspace/glibc/string/explicit_bzero.c.html" rel="nofollow noreferrer noopener" target="_blank">https://code.woboq.org/userspace/glibc/string/explicit_bzero.c.html</a></p>
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