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From: Alex McDonald <blog@rivadpm.com>
Newsgroups: comp.compilers
Subject: Re: Executing from dynamically allocated memory
Date: Sat, 12 Oct 2013 11:12:46 -0700 (PDT)
Organization: Compilers Central
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On Saturday, 12 October 2013 01:05:39 UTC+1, news  wrote:
> In the past, I've malloc'd memory, written machine instructions into it,
> and called the function I built there.
> All this on a 32-bit intel instruction set, on a Debian system. ...

> Now it was a year or three ago that this worked.  Has Linux changed in
> this respect?  Is there something new I have to do to allocate executable
> writable memory for this purpose?
>
> Or might there be something even weirder going on?
> [ Sounds like the NX bit.  See http://en.wikipedia.org/wiki/NX_bit#Linux -John]

mprotect(2) - Linux man page
Name

mprotect - set protection on a region of memory
Synopsis

#include <sys/mman.h>

int mprotect(void *addr, size_t len, int prot);

Description

mprotect() changes protection for the calling process's memory page(s)
containing any part of the address range in the interval [addr,
addr+len-1]. addr must be aligned to a page boundary.

If the calling process tries to access memory in a manner that
violates the protection, then the kernel generates a SIGSEGV signal
for the process.

prot is either PROT_NONE or a bitwise-or of the other values in the
following list:

...

PROT_EXEC

The memory can be executed.

...