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POWeird MIPS assembler behavior with jump (and link) instruction
 

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  1. POWeird MIPS assembler behavior with jump (and link) instruction
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    <p>So, we're studying MIPS architecture at school and we're implementing a MIPS32 architecture. I thought I'd use GNU cross-binutils as assembler but I'm getting weird output when dealing with instructions jal, j and jr. The assembler seems to insert the instructions at the wrong places. I have no idea why this happens, and I doubt the MIPS assembler would be that broken, so I assume this is supposed to happen.</p> <p>Here is my dummy assembly file:</p> <pre><code>.section .text .globl __start __start: addi $a0, $0, 100 addi $a1, $0, 200 jal test test: add $v0, $a0, $a1 jr $ra </code></pre> <p>However, when I disassemble I get this output:</p> <pre><code>Disassembly of section .text: 00000000 &lt;__start&gt;: 0: 20040064 addi a0,zero,100 4: 0c000003 jal c &lt;test&gt; &lt;--- Why is jal coming before addi? 8: 200500c8 addi a1,zero,200 0000000c &lt;test&gt;: c: 03e00008 jr ra &lt;--- Why is jr coming before add? 10: 00851020 add v0,a0,a1 ... </code></pre> <p>Is this some architectural quirk? If so, what is the rationale behind this?</p> <p>EDIT: Tested adding some nop's just for the heck ...</p> <pre><code>.section .text .globl __start __start: addi $a0, $0, 100 addi $a1, $0, 200 nop jal test test: add $v0, $a0, $a1 nop jr $ra </code></pre> <p>and it gives me something that seems somewhat correct.</p> <pre><code>Disassembly of section .text: 00000000 &lt;__start&gt;: 0: 20040064 addi a0,zero,100 4: 200500c8 addi a1,zero,200 8: 0c000004 jal 10 &lt;test&gt; c: 00000000 nop 00000010 &lt;test&gt;: 10: 00851020 add v0,a0,a1 14: 03e00008 jr ra 18: 00000000 nop 1c: 00000000 nop </code></pre> <p>Why are jal and j swapping places with the last instruction?</p>
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    1. COLooks like an endian problem inside the compiler (or the disassembler), just on the command layer instead of the byte layer... strange...
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