[PATCH] Makefile: fix GDB warning with CONFIG_RELR

From: Nick Desaulniers <ndesaulniers@google.com>
To: Masahiro Yamada <masahiroy@kernel.org>
Cc: clang-built-linux@googlegroups.com,
	Fangrui Song <maskray@google.com>,
	Elliot Berman <eberman@quicinc.com>,
	Sami Tolvanen <samitolvanen@google.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Peter Collingbourne <pcc@google.com>,
	Michal Marek <michal.lkml@markovi.net>,
	linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] Makefile: fix GDB warning with CONFIG_RELR
Date: Thu, 18 Mar 2021 17:07:06 -0700	[thread overview]
Message-ID: <20210319000708.1694662-1-ndesaulniers@google.com> (raw)

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>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 Makefile                      | 2 +-
 scripts/tools-support-relr.sh | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 5160ff8903c1..47741cb60995 100644
--- a/Makefile
+++ b/Makefile
@@ -1088,7 +1088,7 @@ 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 45e8aa360b45..cb55878bd5b8 100755
--- 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.
-- 
2.31.0.rc2.261.g7f71774620-goog

