[swift-dev] Standard shared libraries with executable stack

[Ryan Lovelett]

On Mon, Jun 13, 2016, at 11:33 PM, Dmitri Gribenko via swift-dev wrote:
> On Sat, Jun 11, 2016 at 8:12 AM, 김종수 via swift-dev <swift-dev at swift.org>
> wrote:
> > I am testing Swift in "Windows Subsystem for Linux" which is a new feature
> > of Windows 10 Anniversary Update scheduled in this year. WSL is Ubuntu LTS
> > 14.04 compatible in user space.
> >
> > Swift runtime libraries such as libswiftCore.so are marked Executable Stack,
> > which have no problem in Linux.
> >
> > dlopen()'ing swift runtime libraries causes mprotect() with PROT_GROWSDOWN,
> > which is not documented but verified with strace.
> >
> > WSL has not implemented PROT_GROWSDOWN feature because of clean room
> > development.
> >
> > Swift runtime libraries had not been marked Executable Stack before Febrary
> > snapshot. And cmark and llvm/clang shared libraries are not marked too.
> >
> > ***My request is swift runtime libraries be not marked Executable Stack.***
> 
> Hi,
> 
> This could have been caused by our switch from the BFD linker to gold.
> Could you try linking a hello world program using gold linker and
> running it in WSL?

I _think_ this problem existed before the switch from BFD to gold.

I build and package a version of Swift for Linux. During the package
processes makepkg [1] checks the installed binaries for common gotchas
(I tried looking up exactly what is run but could not find it quickly).

My point is that I've been seeing:

swiftc W: ELF file ('usr/bin/swift-test') has executable stack.
swiftc W: ELF file ('usr/bin/repl_swift') has executable stack.
swiftc W: ELF file ('usr/bin/swift-build') has executable stack.
swiftc W: ELF file ('usr/lib/swift/pm/libPackageDescription.so') has
executable stack.
swiftc W: ELF file ('usr/lib/swift/linux/libswiftGlibc.so') has
executable stack.
swiftc W: ELF file ('usr/lib/swift/linux/libXCTest.so') has executable
stack.
swiftc W: ELF file ('usr/lib/swift/linux/libswiftCore.so') has
executable stack.
swiftc W: ELF file ('usr/lib/swift/linux/libFoundation.so') has
executable stack.

Since at least the 20160208a release, but probably longer, I have been
seeing the above errors. That predates the BFD to gold switch by at
least a month. Though I do admit I don't remember the exact date that
change landed.

I have all the build logs dating back to February 22nd if that helps in
anyway. Just food for thought.

[1] https://www.archlinux.org/pacman/makepkg.8.html

> 
> Are you sure that PROT_GROWSDOWN is the flag that enables executable
> stack?  I thought that's what PROT_EXEC is for.  I'm not sure what
> PROT_GROWSDOWN actually changes, if I were to speculate, I'd say it
> could be a marker that means "this is a stack" or maybe even be just a
> performance hint.
> 
> Dmitri
> 
> -- 
> main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
> (j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/
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