[PATCH v2] Makefile: fix GDB warning with CONFIG_RELR

From: Nick Desaulniers <ndesaulniers@google.com>
To: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	Lee Jones <lee.jones@linaro.org>,
	Masahiro Yamada <masahiroy@kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	Fangrui Song <maskray@google.com>,
	Elliot Berman <eberman@quicinc.com>,
	Sami Tolvanen <samitolvanen@google.com>,
	Peter Collingbourne <pcc@google.com>,
	Michal Marek <michal.lkml@markovi.net>,
	linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
	Nick Desaulniers <ndesaulniers@google.com>,
	Nathan Chancellor <nathan@kernel.org>
Subject: [PATCH v2] Makefile: fix GDB warning with CONFIG_RELR
Date: Fri, 21 May 2021 18:26:24 -0700	[thread overview]
Message-ID: <20210522012626.2811297-1-ndesaulniers@google.com> (raw)
In-Reply-To: <CAK7LNAS_LpZnweujqVwZ1kL0eDYR726k35U_yx1djqNE0bk6Rw@mail.gmail.com>

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>
---
Changes V1 -> V2:
* rebase
* pick up Nathan's reviewed by tag.

 Makefile                      | 2 +-
 scripts/tools-support-relr.sh | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 0ed7e061c8e9..2dbb56f831d4 100644
--- 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 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.

base-commit: 45af60e7ced07ae3def41368c3d260dbf496fbce
-- 
2.31.1.818.g46aad6cb9e-goog

