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<p class="MsoNormal"><span lang="EN-GB">Hello LLVM- and Clang-List,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">I’m not sure if this a subject for LLVM or Clang – but there is something I don’t understand. I wrote the following code in C++:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-indent:35.4pt"><span lang="EN-GB" style="font-family:Consolas;color:black">searchPlanschi(&__stdio_common_vswprintf);</span><span lang="EN-GB" style="color:black"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:black">‚searchPlanschi‘ is a function I provide. Clang generates the following assembly code for this:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:Consolas;color:black"> lea rcx, [rip + __stdio_common_vswprintf]<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:Consolas;color:black"> call "?searchPlanschi@@YAXPEAX@Z"<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:black">I was surprised to see the register rip there, as far as I know this is the Instruction register, right? Why do I need the rip register to get the address of the function? I searched the assembly file
for ‘__stdio_common_vswprintf’ to get some hints about this. The only thing I found was:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:Consolas;color:black"> .addrsig<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:Consolas;color:black"> .addrsig_sym __stdio_common_vswprintf<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:black">So I googled “.addrsig” and found the following text:<o:p></o:p></span></p>
<p><span lang="EN-GB">“This section is used to mark symbols as address-significant, i.e. the address of the symbol is used in a comparison or leaks outside the translation unit. It has the same meaning as the absence of the LLVM attributes unnamed_addr and
local_unnamed_addr.<br>
Any sections referred to by symbols that are not marked as address-significant in any object file may be safely merged by a linker without breaking the address uniqueness guarantee provided by the C and C++ language standards.<br>
The contents of the section are a sequence of ULEB128-encoded integers referring to the symbol table indexes of the address-significant symbols.”<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:black">But sadly… this is way over my head. What does that actually mean? Does that explain the code construct with the rip register? Is that a form of optimization?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:black">Thank you in advance for any help!<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:black">Kind greetings<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:black">Björn<o:p></o:p></span></p>
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