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copied!<p>It would really help to know what gcc version you are using and what libc. It looks like you have a very old gcc version or a strange platform or both. What's going on is some strangeness with calling conventions. I can tell you a few things:</p> <p>Save the frame pointer on the stack according to convention:</p> <pre><code>pushl %ebp movl %esp, %ebp </code></pre> <p>Make room for stuff at the old end of the frame, and round the stack pointer down to a multiple of 4 (why this is needed I don't know):</p> <pre><code>subl $8, %esp andl $-16, %esp </code></pre> <p>Through an insane song and dance, get ready to return 1 from <code>main</code>:</p> <pre><code>movl $0, %eax addl $15, %eax addl $15, %eax shrl $4, %eax sall $4, %eax movl %eax, -4(%ebp) movl -4(%ebp), %eax </code></pre> <p>Recover any memory allocated with <code>alloca</code> (GNU-ism):</p> <pre><code>call __alloca </code></pre> <p>Announce to libc that <code>main</code> is exiting (more GNU-ism):</p> <pre><code>call ___main </code></pre> <p>Restore the frame and stack pointers:</p> <pre><code>leave </code></pre> <p>Return:</p> <pre><code>ret </code></pre> <p>Here's what happens when I compile the very same source code with gcc 4.3 on Debian Linux:</p> <pre><code> .file "main.c" .text .p2align 4,,15 .globl main .type main, @function main: leal 4(%esp), %ecx andl $-16, %esp pushl -4(%ecx) pushl %ebp movl %esp, %ebp pushl %ecx popl %ecx popl %ebp leal -4(%ecx), %esp ret .size main, .-main .ident "GCC: (Debian 4.3.2-1.1) 4.3.2" .section .note.GNU-stack,"",@progbits </code></pre> <p>And I break it down this way:</p> <p>Tell the debugger and other tools the source file:</p> <pre><code> .file "main.c" </code></pre> <p>Code goes in the text section:</p> <pre><code> .text </code></pre> <p>Beats me:</p> <pre><code> .p2align 4,,15 </code></pre> <p><code>main</code> is an exported function:</p> <pre><code>.globl main .type main, @function </code></pre> <p><code>main</code>'s entry point:</p> <pre><code>main: </code></pre> <p>Grab the return address, align the stack on a 4-byte address, and save the return address again (why I can't say):</p> <pre><code> leal 4(%esp), %ecx andl $-16, %esp pushl -4(%ecx) </code></pre> <p>Save frame pointer using standard convention:</p> <pre><code> pushl %ebp movl %esp, %ebp </code></pre> <p>Inscrutable madness:</p> <pre><code> pushl %ecx popl %ecx </code></pre> <p>Restore the frame pointer and the stack pointer:</p> <pre><code> popl %ebp leal -4(%ecx), %esp </code></pre> <p>Return:</p> <pre><code> ret </code></pre> <p>More info for the debugger?:</p> <pre><code> .size main, .-main .ident "GCC: (Debian 4.3.2-1.1) 4.3.2" .section .note.GNU-stack,"",@progbits </code></pre> <p>By the way, <code>main</code> is special and magical; when I compile</p> <pre><code>int f(void) { return 17; } </code></pre> <p>I get something slightly more sane:</p> <pre><code> .file "f.c" .text .p2align 4,,15 .globl f .type f, @function f: pushl %ebp movl $17, %eax movl %esp, %ebp popl %ebp ret .size f, .-f .ident "GCC: (Debian 4.3.2-1.1) 4.3.2" .section .note.GNU-stack,"",@progbits </code></pre> <p>There's still a ton of decoration, and we're still saving the frame pointer, moving it, and restoring it, which is utterly pointless, but the rest of the code make sense.</p>

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