Re: [BUG] Force to use a dynamic linker in musl-clang wapper cause a crash for static-pie c++ programs.

[Youren Shen <shenyouren@gmail.com>]

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Thanks for your reply.

Dived deeper, I think this is because the options clang/gcc passed to ld
are not well handled by ld. Unlike "-static", which is passed directly to
the linker, the clang pass -no-dynamic-linker when static-pie is enabled.
However, -dynamic-linker=<file> in ld.musl-clang wrapper conflict with this
-no-dynamic-linker. As a result, ld accepts the last one it received, which
is "-dynamic-linker=<file>" in this case. Here is the problem: even we
passed static-pie to clang, and then the clang pass -no-dynamic-linker to
ld, This option is still omitted by ld.musl-clang. I suggest a fix on it:
move -dynamic-linker "$ldso" before the previous user inputs.
Before:
```
exec $($cc -print-prog-name=ld) -nostdlib "$@" -lc -dynamic-linker "$ldso"
```
After:
```
 exec $($cc -print-prog-name=ld) -nostdlib -dynamic-linker "$ldso" "$@" -lc
```
As you can see, this is a quite simple patch. Further testes may required.
And for musl-gcc, as I test, it seems that it has the same problem. But I'm
not familiar with gcc specs file. So maybe if anyone encounter the same
problem, they can refer this email and give a solution.

On Tue, Dec 24, 2019 at 11:03 PM Rich Felker <dalias@libc.org> wrote:

> On Tue, Dec 24, 2019 at 10:38:49PM +0800, Youren Shen wrote:
> > Hey, there,
> > Recently I'm trying to build a non-gnu toolchain with musl, clang, llvm,
> > libc++, compiler-rt. While static-pie feature is very useful in our
> > project, musl-clang force to link a dynamic linker into the binary. This
> > behavior will cause a crash in c++ programs with compiler-rt and libc++.
> > For more details and reproduction of this bug, you can read my previous
> > email to llvm-dev mail lists.[1]
> > I spend a few days to find the reason -- in function _dlstart_c, the
> > program will get a "base" of relocation in /lib/ld-musl-x86_64.so.1,
> which
> > is not right when it tries to relocate .rel.dyn section in the binary.
> > Overall, the static-pie program does not need a dynamic linker at all. So
> > maybe we should remove this argument in wrapper when static-pie is
> enabled.
> >
> > Thank you very much.
> >
> > [1].
> https://groups.google.com/forum/#!msg/llvm-dev/XPrSPqD2zjM/YtH6Fi2YAgAJ
>
> I don't think the wrappers (gcc or clang one) have been updated with
> logic for static pie since it was added, and I'm not sure how easy it
> is to add. I'd welcome patches for review, though.
>
> Rich
>


-- 
Best Regards.
Youren Shen.

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diff --git a/tools/ld.musl-clang.in b/tools/ld.musl-clang.in
index 93763d6..7cb49d9 100644
--- a/tools/ld.musl-clang.in
+++ b/tools/ld.musl-clang.in
@@ -48,4 +48,4 @@ for x ; do
     esac
 done

-exec $($cc -print-prog-name=ld) -nostdlib "$@" -lc -dynamic-linker "$ldso"
+exec $($cc -print-prog-name=ld) -nostdlib -dynamic-linker "$ldso" "$@" -lc