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POCalling NASM from a C program using system() produces different object code then calling using Bash
 

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  1. POCalling NASM from a C program using system() produces different object code then calling using Bash
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    <p>I've implemented a reasonably good optimizing compiler (for a toy language), and have come across a rather puzzling scenario. I can take an input file and produce assembly from it, so in that respect the "compiler" is finished. If I take that assembly file assemble it with NASM and link it to my runtime support library with G++ (the runtime needs libstdc++), I get a working executable, with no errors. However, I'd like to be able to compile to an executable in one command, so I added some calls to <code>system</code> to my compiler, passing the EXACT SAME COMMANDS as I was using in bash. When I run the compiler, it seems to assembly properly, but the linking step (again, using g++) fails with an <code>undefined reference to main</code>. Confused, I attempted to link manually (without reassembling, so I was using the object file produced by the NASM run with <code>system</code>, and received the same error. If I reassemble using the new compiler's assembly output, I have no problems, which has led be to believe that NASM is the problem. Like I said, the commands are exactly the same (I literally copied and pasted them just to make sure after the first time). Is this environment variables or something? What's going on?</p> <p>EDIT: I manually assembled an object file, again using the same command as the one in the compiler, and I did a vim diff between the two. The compiler-generated one seems to only contain the ELF header.</p> <p>EDIT 2: A screenshot of the diff<img src="https://i.stack.imgur.com/qnshr.png" alt="screenshot"></p> <p>EDIT 3: I tried using <code>system</code> to call a Perl script that in turn would call NASM and G++, still no luck.</p>
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    1. USSamuel Breese
    1. USSamuel Breese
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    1. COGood and hard question, +1.
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    2. COThanks. I try to refrain from asking here until I've been stumped for a few days of constant searching :P
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      1. USSamuel Breese
    3. COWhat about environment variables, is it possible the GCC reads from them?
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      1. POCalling NASM from a C program using system() produces different object code then calling using Bash
      1. USRichard J. Ross III
 

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