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<p class="MsoNormal">Hi, <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’ve been attempting to call a C++ function from LLVM code. The LLVM code is JIT’ted and executed from C++. Basically my idea was as follows:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">-- LLVM IR code –<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">; ModuleID = 'native'<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">define i32 @main(i32, i8**) {<o:p></o:p></p>
<p class="MsoNormal">code:<o:p></o:p></p>
<p class="MsoNormal"> call void @"Helper::Test"(i128 128932)<o:p></o:p></p>
<p class="MsoNormal"> ret i32 0<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">-- C++ code – <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">struct int128 <o:p></o:p></p>
<p class="MsoNormal">{<o:p></o:p></p>
<p class="MsoNormal"> uint64_t v1; <o:p></o:p></p>
<p class="MsoNormal"> uint64_t v2; <o:p></o:p></p>
<p class="MsoNormal"> // … code omitted… *1<o:p></o:p></p>
<p class="MsoNormal">};<o:p></o:p></p>
<p class="MsoNormal" style="background:white"><span style="font-size:10.0pt;font-family:Consolas;color:black"><o:p> </o:p></span></p>
<p class="MsoNormal" style="background:white"><span style="font-size:10.0pt;font-family:Consolas;color:blue">struct</span><span style="font-size:10.0pt;font-family:Consolas;color:black"> </span><span style="font-size:10.0pt;font-family:Consolas;color:#2B91AF">Helper</span><span style="font-size:10.0pt;font-family:Consolas;color:black"><o:p></o:p></span></p>
<p class="MsoNormal" style="background:white"><span style="font-size:10.0pt;font-family:Consolas;color:black">{<o:p></o:p></span></p>
<p class="MsoNormal" style="background:white"><span style="font-size:10.0pt;font-family:Consolas;color:black">
</span><span style="font-size:10.0pt;font-family:Consolas;color:blue">static</span><span style="font-size:10.0pt;font-family:Consolas;color:black"> </span><span style="font-size:10.0pt;font-family:Consolas;color:blue">void</span><span style="font-size:10.0pt;font-family:Consolas;color:black"> Test(</span><span style="font-size:10.0pt;font-family:Consolas;color:#2B91AF">int128</span><span style="font-size:10.0pt;font-family:Consolas;color:black"> </span><span style="font-size:10.0pt;font-family:Consolas;color:gray">value</span><span style="font-size:10.0pt;font-family:Consolas;color:black">)<o:p></o:p></span></p>
<p class="MsoNormal" style="background:white"><span style="font-size:10.0pt;font-family:Consolas;color:black"> {<o:p></o:p></span></p>
<p class="MsoNormal" style="background:white"><span style="font-size:10.0pt;font-family:Consolas;color:black"> }<o:p></o:p></span></p>
<p class="MsoNormal" style="background:white"><span style="font-size:10.0pt;font-family:Consolas;color:black">};<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">If I try to execute the code, I notice that MSVC++ seems to expect a pointer. Most notably, if you implement the copy constructor: int128(const int128& o) { … } , the address of o will be 128932 . As for assembler output, I noticed that
%ecx is set to the value, %edx is zero’d and then the method is called. <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">As evidenced by the resulting crash, this is apparently not the right way to do something like this… Obviously, I can also try to pass the value by pointer - but will then get issues with return values. Alternatively, I can introduce a
2x64-bit structure, fill that with the int128 and pass that.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">My question is: what’s the correct way to do something like this?
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Kind regards,<o:p></o:p></p>
<p class="MsoNormal">Stefan.<o:p></o:p></p>
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