linux-kernel - [PATCH v3] Makefile: use -z pack-relative-relocs

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Date:   Tue, 11 Apr 2023 20:09:44 +0000
From:   Fangrui Song <maskray@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Peter Collingbourne <pcc@...gle.com>,
        Will Deacon <will@...nel.org>,
        Fangrui Song <maskray@...gle.com>
Subject: [PATCH v3] Makefile: use -z pack-relative-relocs

Commit 27f2a4db76e8 ("Makefile: fix GDB warning with CONFIG_RELR")
added --use-android-relr-tags to fix a GDB warning

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

The GDB warning has been fixed in version 11.2.

The DT_ANDROID_RELR tag was deprecated since DT_RELR was standardized.
Thus, --use-android-relr-tags should be removed. While making the
change, try -z pack-relative-relocs, which is supported since LLD 15.
Keep supporting --pack-dyn-relocs=relr as well for older LLD versions.
There is no indication of obsolescence for --pack-dyn-relocs=relr.

As of today, GNU ld supports the latter option for x86 and powerpc64
ports and has no intention to support --pack-dyn-relocs=relr. In the
absence of the glibc symbol version GLIBC_ABI_DT_RELR,
--pack-dyn-relocs=relr and -z pack-relative-relocs are identical in
ld.lld.

GNU ld and newer versions of LLD report warnings (instead of errors) for
unknown -z options. Only errors lead to non-zero exit codes. Therefore,
we should test --pack-dyn-relocs=relr before testing
-z pack-relative-relocs.

Link: https://github.com/ClangBuiltLinux/linux/issues/1057
Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=a619b58721f0a03fd91c27670d3e4c2fb0d88f1e
Signed-off-by: Fangrui Song <maskray@...gle.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
 Makefile                      | 3 ++-
 scripts/tools-support-relr.sh | 8 ++++++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index 5aeea3d98fc0..d9c6d1839cf0 100644
--- a/Makefile
+++ b/Makefile
@@ -1113,7 +1113,8 @@ LDFLAGS_vmlinux	+= -X
 endif
 
 ifeq ($(CONFIG_RELR),y)
-LDFLAGS_vmlinux	+= --pack-dyn-relocs=relr --use-android-relr-tags
+# ld.lld before 15 did not support -z pack-relative-relocs.
+LDFLAGS_vmlinux	+= $(call ld-option,--pack-dyn-relocs=relr,-z pack-relative-relocs)
 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 cb55878bd5b8..4c121946e517 100755
--- a/scripts/tools-support-relr.sh
+++ b/scripts/tools-support-relr.sh
@@ -7,8 +7,12 @@ 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 \
-  --use-android-relr-tags -o $tmp_file
+
+# ld.lld before 15 did not support -z pack-relative-relocs.
+if ! $LD $tmp_file.o -shared -Bsymbolic --pack-dyn-relocs=relr -o $tmp_file 2>/dev/null; then
+	$LD $tmp_file.o -shared -Bsymbolic -z pack-relative-relocs -o $tmp_file 2>&1 |
+		grep -q pack-relative-relocs && exit 1
+fi
 
 # 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.
-- 
2.40.0.577.gac1e443424-goog