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POWhy is the ELF entry point 0x8048000 not changeable with the "ld -e" option?
 

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  1. POWhy is the ELF entry point 0x8048000 not changeable with the "ld -e" option?
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    <p>Following up <a href="https://stackoverflow.com/questions/2187484/elf-binary-entry-point">Why is the ELF execution entry point virtual address of the form 0x80xxxxx and not zero 0x0?</a> and <a href="https://stackoverflow.com/questions/2966426/why-do-virtual-memory-addresses-for-linux-binaries-start-at-0x8048000">Why do virtual memory addresses for linux binaries start at 0x8048000?</a>, why cannot I make <code>ld</code> use a different entry point than the default with <code>ld -e</code>?</p> <p>If I do so, I either get a <code>segmentation fault</code> with return code 139, even for addresses close by the default entry point. Why?</p> <p><strong>EDIT:</strong></p> <p>I will make the question more specific:</p> <pre><code> .text .globl _start _start: movl $0x4,%eax # eax = code for 'write' system call movl $1,%ebx # ebx = file descriptor to standard output movl $message,%ecx # ecx = pointer to the message movl $13,%edx # edx = length of the message int $0x80 # make the system call movl $0x0,%ebx # the status returned by 'exit' movl $0x1,%eax # eax = code for 'exit' system call int $0x80 # make the system call .data .globl message message: .string "Hello world\n" # The message as data </code></pre> <p>If I compile this with <code>as program.s -o program.o</code> and then link it statically with <code>ld -N program.o -o program</code>, <code>readelf -l program</code> shows <code>0x0000000000400078</code> as the <code>VirtAddr</code> of the text segment and <code>0x400078</code> as entry point. When run, `Hello world" is printed.</p> <p>However, when I try to link with <code>ld -N -e0x400082 -Ttext=0x400082 program.o -o program</code> (moving text segment and entry point by 4 bytes), the program will be <code>killed</code>. Inspecting it with <code>readelf -l</code> now shows two different headers of type <code>LOAD</code>, one at <code>0x0000000000400082</code> and one at <code>0x00000000004000b0</code>.</p> <p>When I try <code>0x400086</code>, it all works, and there is only one <code>LOAD</code> section.</p> <ol> <li>What's going on here?</li> <li>Which memory addresses may I chose, which ones cannot I chose and why?</li> </ol> <p>Thanks you.</p>
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