Makefile: fix GDB warning with CONFIG_RELR

GDB produces the following warning when debugging kernels built with
CONFIG_RELR:

BFD: /android0/linux-next/vmlinux: unknown type [0x13] section `.relr.dyn'

when loading a kernel built with CONFIG_RELR into GDB. It can also
prevent debugging symbols using such relocations.

Peter sugguests:
  [That flag] means that lld will use dynamic tags and section type
  numbers in the OS-specific range rather than the generic range. The
  kernel itself doesn't care about these numbers; it determines the
  location of the RELR section using symbols defined by a linker script.

Link: https://github.com/ClangBuiltLinux/linux/issues/1057
Suggested-by: Peter Collingbourne <pcc@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20210522012626.2811297-1-ndesaulniers@google.com
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/Makefile b/Makefile
index e4468353425a65f1c609c93b76007accf5e8e0aa..e38c74d0433c247c5923bbdc3cc0e9877f7ea48d 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -1031,7 +1031,7 @@ LDFLAGS_vmlinux   += $(call ld-option, -X,)
 endif
 
 ifeq ($(CONFIG_RELR),y)
-LDFLAGS_vmlinux        += --pack-dyn-relocs=relr
+LDFLAGS_vmlinux        += --pack-dyn-relocs=relr --use-android-relr-tags
 endif
 
 # We never want expected sections to be placed heuristically by the

diff --git a/scripts/tools-support-relr.sh b/scripts/tools-support-relr.sh
index 45e8aa360b45745e7134a24c32e0c4343a6c3303..cb55878bd5b815a031d883de9a8600feef8ab39d 100755 (executable)
--- a/scripts/tools-support-relr.sh
+++ b/scripts/tools-support-relr.sh
@@ -7,7 +7,8 @@ trap "rm -f $tmp_file.o $tmp_file $tmp_file.bin" EXIT
 cat << "END" | $CC -c -x c - -o $tmp_file.o >/dev/null 2>&1
 void *p = &p;
 END
-$LD $tmp_file.o -shared -Bsymbolic --pack-dyn-relocs=relr -o $tmp_file
+$LD $tmp_file.o -shared -Bsymbolic --pack-dyn-relocs=relr \
+  --use-android-relr-tags -o $tmp_file
 
 # Despite printing an error message, GNU nm still exits with exit code 0 if it
 # sees a relr section. So we need to check that nothing is printed to stderr.