Re: PT_GNU_STACK and PT_GNU_HEAP

[Ian Lance Taylor <iant at google dot com>]

Jeffrey Walton <noloader@gmail.com> writes:

> I'm looking for reading on PT_GNU_STACK and PT_GNU_HEAP. The Gentoo
> documentation I have seen states GCC will add PT_GNU_STACK and
> PT_GNU_HEAP markings to the binary if compiled from non-asm files. If
> compiling ASM files, the markings are not added. The docs also state
> PaX ignores the markings (PaX offers no-execute plus more).
>
> Other than Gentoo documentation, I'm not finding much reading on GCC
> and PT_GNU_STACK and PT_GNU_HEAP.

I described PT_GNU_STACK here: http://www.airs.com/blog/archives/518 .

I believe that PT_GNU_HEAP is a Gentoo extension.  I'm not aware of it
existing on any other system.  Gentoo appears to handle PT_GNU_HEAP just
like PT_GNU_STACK, with a .note.GNU-heap section.  The heap is of course
normally not executable.  I assume that the presence of a PT_GNU_HEAP
segment without executable permission means that the kernel denies
attempts to call mprotect to mark the heap as executable.  But I'm just
guessing--I don't know for sure.  I don't see any use of PT_GNU_HEAP in
the Linux kernel sources I have lying around.

Ian