Re: [PATCH] fix musl-gcc.specs.sh to correctly handle -static-pie

[Rich Felker <dalias@libc.org>]

On Tue, May 28, 2019 at 10:19:18PM +0200, Ferdi265 wrote:
> Hello,
> 
> Today I wanted to use musl-gcc to build -static-pie binaries. I noticed
> that this does not work (musl-libc is still linked as a shared library
> and is also still requested as an interpreter).
> 
> Looking into the musl-gcc.specs file the bug was obvious: rcrt1.o was
> not used as a startfile, and neither -no-dynamic-linker nor -static were
> passed to the linker.
> 
> This patch fixes this by actually using rcrt1.o and passing the linker
> options when -static-pie is given.
> 
> I don't have much experience with the specifics of gcc .spec files and
> which options need to be passed, but this seems to work with all
> variations of -shared, -static, and -static-pie that I've tried.
> 
> Here (https://github.com/Ferdi265/musl) is the repository with the patch
> on GitHub, and I've also attached the patch below.
> 
> Greetings,
> Ferdinand "Ferdi265" Bachmann
> 
> --- PATCH BELOW ---
> 
> From 070bce8f7e508a951d3b65da227b2fca3a65f37b Mon Sep 17 00:00:00 2001
> From: Ferdinand Bachmann <theferdi265@gmail.com>
> Date: Tue, 28 May 2019 21:53:25 +0200
> Subject: [PATCH] fix musl-gcc.specs.sh to correctly handle -static-pie
> 
> ---
>  tools/musl-gcc.specs.sh | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/musl-gcc.specs.sh b/tools/musl-gcc.specs.sh
> index 30492574..7206cb25 100644
> --- a/tools/musl-gcc.specs.sh
> +++ b/tools/musl-gcc.specs.sh
> @@ -17,13 +17,13 @@ cat <<EOF
>  libgcc.a%s %:if-exists(libgcc_eh.a%s)
> 
>  *startfile:
> -%{!shared: $libdir/Scrt1.o} $libdir/crti.o crtbeginS.o%s
> +%{static-pie: $libdir/rcrt1.o} %{!static-pie: %{!shared:
> $libdir/Scrt1.o}} $libdir/crti.o crtbeginS.o%s
> 
>  *endfile:
>  crtendS.o%s $libdir/crtn.o
> 
>  *link:
> --dynamic-linker $ldso -nostdlib %{shared:-shared} %{static:-static}
> %{rdynamic:-export-dynamic}
> +%{static-pie:-no-dynamic-linker -static} %{!static-pie:-dynamic-linker
> $ldso} -nostdlib %{shared:-shared} %{static:-static}
> %{rdynamic:-export-dynamic}
> 
>  *esp_link:
> 

This looks okay-ish, but could be improved. GCC spec syntax doesn't
require separate static-pie and !static-pie conditions; it supports
"else" with notation:

	%{static-pie:-no-dynamic-linker -static;-dynamic-linker $ldso}

There's also the question of whether we should make -static -pie work
like it's intended to by us, or like gcc does it upstream (ignoring
-pie). I think it's hard to duplicate the behavior we want since it
depends on knowing if the compiler was built as default-pie, so the
way you've done it is probably the best we can easily do, and at least
non-broken.

Anyone else have comments on this?

Rich