Re: [PATCH] mips: Add appropriate linker flags when compiling with -static-pie

[linted <linted90@gmail.com>]

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On Wed, Oct 12, 2022 at 2:18 PM Jeff Law via Gcc-patches <
gcc-patches@gcc.gnu.org> wrote:

>
> On 9/25/22 09:49, linted via Gcc-patches wrote:
> > Hello,
> > I'm just checking to see if anyone has had a chance to look at this.
> >
> > Thank you
> >
> > On Wed, Sep 14, 2022 at 2:09 PM linted <linted90@gmail.com> wrote:
> >
> >> Hello,
> >>
> >> This patch fixes missing flags when compiling with -static-pie on mips.
> I
> >> made these modifications based on the previously submitted static pie
> patch
> >> for arm as well as the working code for aarch64.
> >>
> >> I tested with a host of mips-elf and checked with mips-sim. This patch
> was
> >> also tested and used with uclibc-ng to generate static pie elfs.
> >>
> >> This is my first patch for gcc, so please let me know if there is
> anything
> >> I missed.
> >>
> >>
> >>
> >> Signed-off-by: linted <linted@users.noreply.github.com>
> >> ---
> >>   gcc/config/mips/gnu-user.h | 5 +++--
> >>   1 file changed, 3 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/gcc/config/mips/gnu-user.h b/gcc/config/mips/gnu-user.h
> >> index 6aad7192e69..b1c665b7f37 100644
> >> --- a/gcc/config/mips/gnu-user.h
> >> +++ b/gcc/config/mips/gnu-user.h
> >> @@ -56,11 +56,12 @@ along with GCC; see the file COPYING3.  If not see
> >>   #define GNU_USER_TARGET_LINK_SPEC "\
> >>     %{G*} %{EB} %{EL} %{mips*} %{shared} \
> >>     %{!shared: \
> >> -    %{!static: \
> >> +    %{!static:%{!static-pie: \
> >>         %{rdynamic:-export-dynamic} \
> >>         %{mabi=n32: -dynamic-linker " GNU_USER_DYNAMIC_LINKERN32 "} \
> >>         %{mabi=64: -dynamic-linker " GNU_USER_DYNAMIC_LINKER64 "} \
> >> -      %{mabi=32: -dynamic-linker " GNU_USER_DYNAMIC_LINKER32 "}} \
> >> +      %{mabi=32: -dynamic-linker " GNU_USER_DYNAMIC_LINKER32 "}}} \
> >> +    %{static-pie:-Bstatic -pie --no-dynamic-linker -z text} \
> >>       %{static}} \
>
> This is a bit out of my usual areas of expertise.  But what I find odd
> here is that for -static we essentially do nothing, but for -static-pie
> we need "-Bstatic -pie --no-dynamic-linker -z text".    Is the -Bstatic
> really needed for static-pie  And if it is, then wouldn't it be needed
> for -static as well?    If you look carefully at aarch64, you'll see it
> includes -Bstatic for -static.
>
>
> Jeff
>

This is a really good question. From what I can tell, the linker will treat
-Bstatic and -static identically. So when compiling with -static, adding a
-Bstatic is redundant since the -static will be passed on to the linker.

In the case of -static-pie, we need to explicitly specify -Bstatic so that
the linker will know that we want the binary to be statically linked since
there is no -static being passed on.

I am of the opinion that we should usually be explicit, but in this case, I
think it is more prudent to change less code.