Why data and stack segments are executable?

On modern Linux systems, the linker will mark stack/data non-executable IFF all objects that participate in the link have a special “marker” section .note.GNU-stack.

If you compile e.g. int foo() { return 1; } into assembly (with gcc -S foo.c), you’ll see this:

    .section    .note.GNU-stack,"",@progbits

For nasm, the syntax is shown in section 8.9.2 of the manual; you want something like this:

 section .note.GNU-stack noalloc noexec nowrite progbits

Note

This has to be done for every .o file that goes into the executable. If any object file needs executable stack or data, then it’s set for the entire segment.

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