Re: Executing from dynamically allocated memory

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From	"James Harris" <james.harris.1@gmail.com>
Newsgroups	comp.compilers
Subject	Re: Executing from dynamically allocated memory
Date	Sat, 12 Oct 2013 10:10:51 +0100
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"news" <news@fx32.iad.highwinds-media.com> wrote in message
> 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.
>
> This appears no longer too work.  My program gives a segmentation fault.
> The debugger tells me that the segmentation fault occurs on the first
> instruction of the called function, a
> push   %ebp
> residing in malloced memory.
>
> 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?

Possibly. As John says, this could be caused by current Linux setting the NX
bit for malloced pages. The dump may/should show if that is the case, if you
can decipher the dump.

Instead of malloc you may need to use mmap. It allows permissions to be
specified.

James

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Executing from dynamically allocated memory "news" <news@fx32.iad.highwinds-media.com> - 2013-10-12 00:05 +0000
  Re: Executing from dynamically allocated memory "James Harris" <james.harris.1@gmail.com> - 2013-10-12 10:10 +0100
  Re: Executing from dynamically allocated memory Sébastien Fricker <sebastien.fricker@gmail.com> - 2013-10-12 11:52 +0200
  Re: Executing from dynamically allocated memory chakaram@auth.gr - 2013-10-12 19:20 +0300
  Re: Executing from dynamically allocated memory Alex McDonald <blog@rivadpm.com> - 2013-10-12 11:12 -0700
  Re: Executing from dynamically allocated memory sandmann@cs.au.dk (Søren Sandmann) - 2013-10-12 20:58 +0200
  Re: Executing from dynamically allocated memory Jens Kallup <jkallup@web.de> - 2013-10-13 10:44 +0200

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