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<a href="https://gitlab.com/rockdaboot">Tim Rühsen</a>
commented:
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<p dir="auto">Valgrind doens't complain when built with -O0, the assembler (L122/strcmp starts at the arrow):</p>
<pre class="code highlight js-syntax-highlight plaintext" lang="plaintext" v-pre="true"><code><span id="LC1" class="line" lang="plaintext"> 0x00005555555554f8 <+803>: mov $0x76,%esi</span>
<span id="LC2" class="line" lang="plaintext"> 0x00005555555554fd <+808>: lea 0xb14(%rip),%rdi # 0x555555556018</span>
<span id="LC3" class="line" lang="plaintext"> 0x0000555555555504 <+815>: mov $0x0,%eax</span>
<span id="LC4" class="line" lang="plaintext"> 0x0000555555555509 <+820>: callq 0x555555555060 <printf@plt></span>
<span id="LC5" class="line" lang="plaintext"> 0x000055555555550e <+825>: mov $0x1,%edi</span>
<span id="LC6" class="line" lang="plaintext"> 0x0000555555555513 <+830>: callq 0x5555555550b0 <exit@plt></span>
<span id="LC7" class="line" lang="plaintext">=> 0x0000555555555518 <+835>: lea -0x4b0(%rbp),%rax</span>
<span id="LC8" class="line" lang="plaintext"> 0x000055555555551f <+842>: lea 0xb4c(%rip),%rsi # 0x555555556072</span>
<span id="LC9" class="line" lang="plaintext"> 0x0000555555555526 <+849>: mov %rax,%rdi</span>
<span id="LC10" class="line" lang="plaintext"> 0x0000555555555529 <+852>: callq 0x555555555080 <strcmp@plt></span>
<span id="LC11" class="line" lang="plaintext"> 0x000055555555552e <+857>: test %eax,%eax</span>
<span id="LC12" class="line" lang="plaintext"> 0x0000555555555530 <+859>: jne 0x555555555552 <main+893></span>
<span id="LC13" class="line" lang="plaintext"> 0x0000555555555532 <+861>: mov $0x7c,%esi</span>
<span id="LC14" class="line" lang="plaintext"> 0x0000555555555537 <+866>: lea 0xada(%rip),%rdi # 0x555555556018</span></code></pre>
<p dir="auto">In comparison, the code generated by gcc 9 with -O2 (see above) just accesses 16 bytes of stack memory for an optimized version of <code>strcmp</code>. So no wonder that valgrind complains, though it is a false positive.</p>
<p dir="auto">To calm down valgrind, we can <code>*data = 0</code> before <code>asn1_read_value()</code>. This just 'marks' <code>data</code> as being initialized. Alternatively, we have to add/create a valgrind suppression.</p>
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