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Re: Executable memory: some apps that work on RH9 don't on FC1



On Mon, Nov 17, 2003 at 01:54:55PM +0100, Gerard Milmeister wrote:
> Some software, among them clisp, scm and mit-scheme don't work anymore
> with FC1. One problem seems to be that on FC1 stack and malloced memory
> is no longer executable, at least not without using mprotect.
> Interpreters and compilers like the above commonly allocate a piece of
> memory and fill it with executable code. I am sure they can be adapted
> to work on FC1, but I would have preferred that the FC1 kernel would
> behave in the same way as the RH9 one. Is there any way to disable this
> behaviour. Trying to get the problem fixed by the upstream developers
> will probably take a long time, and it seems that other Linux distros
> don't show this problem...

If they need executable stack in a way which is not known to the compiler,
the programmer has to tell it to the toolchain.
If a program say takes address of a nested function, GCC knows it needs
executable stack and arranges things automatically.
Otherwise, either an object file can be marked as needing executable
stack (with -Wa,--execstack; at least one such object will make the whole
shared library or binary requiring executable stack), or during link
time with -Wl,-z,execstack or after it using execstack(8) utility.
The defaults are such that programs and/or libraries compiled/linked
on <= RHL9 are always assumed to potentially require executable stack,
but if you build a new program on FC1, you really need to tell the toolchain
about it.

	Jakub




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