[PATCH] powerpc/wrapper: add "-z rodynamic" when using LLD

[Fangrui Song]

We could wait for https://lkml.org/lkml/2020/11/13/19
"[PATCH] kbuild: Always link with '-z norelro'"

Then we would not need -z rodynamic to work around a -z relro issue.

(The issue is that some sections don't strictly follow the normal
R/RX/RW(RELRO)/RW(non-RELRO) section flag partition. As a linker person
I would suggest that we don't create multiple clusters with the same
section flags (e.g. RW in two separate places), but this is my very
minor complaint.)

On 2020-11-18, Bill Wendling wrote:
>Normally all read-only sections precede SHF_WRITE sections. .dynamic and
>.got have the SHF_WRITE flag; .dynamic probably because of DT_DEBUG. LLD
>emits an error when this happens, so use "-z rodynamic" to mark .dynamic
>as read-only.
>
>Cc: Fangrui Song <maskray at google.com>
>Cc: Alan Modra <amodra at gmail.com>
>Signed-off-by: Bill Wendling <morbo at google.com>
>---
> arch/powerpc/boot/wrapper | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
>diff --git a/arch/powerpc/boot/wrapper b/arch/powerpc/boot/wrapper
>index cd58a62e810d..e1194955adbb 100755
>--- a/arch/powerpc/boot/wrapper
>+++ b/arch/powerpc/boot/wrapper
>@@ -46,6 +46,7 @@ compression=.gz
> uboot_comp=gzip
> pie=
> format=
>+rodynamic=
>
> # cross-compilation prefix
> CROSS=
>@@ -353,6 +354,7 @@ epapr)
>     platformo="$object/pseries-head.o $object/epapr.o $object/epapr-wrapper.o"
>     link_address='0x20000000'
>     pie=-pie
>+    rodynamic=$(if ${CROSS}ld -V 2>&1 | grep -q LLD ; then echo "-z rodynamic"; fi)
>     ;;
> mvme5100)
>     platformo="$object/fixed-head.o $object/mvme5100.o"
>@@ -493,7 +495,7 @@ if [ "$platform" != "miboot" ]; then
>         text_start="-Ttext $link_address"
>     fi
> #link everything
>-    ${CROSS}ld -m $format -T $lds $text_start $pie $nodl -o "$ofile" $map \
>+    ${CROSS}ld -m $format -T $lds $text_start $pie $nodl $rodynamic -o "$ofile" $map \
> 	$platformo $tmp $object/wrapper.a
>     rm $tmp
> fi
>-- 
>2.29.2.454.gaff20da3a2-goog
>