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, replace --pack-dyn-relocs=relr with -z pack-relative-relocs,
which is supported since LLD 15.

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.

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

Hi Fangrui,
Thanks for the patches!

On Thu, Mar 23, 2023 at 1:44 PM Fangrui Song <maskray@google.com> wrote:
>
> 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, replace --pack-dyn-relocs=relr with -z pack-relative-relocs,
> which is supported since LLD 15.

Looks like
commit 4a8de2832a2a ("[ELF] Add -z pack-relative-relocs")

>
> 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.

Won't this regress support for CONFIG_TOOLS_SUPPORT_RELR for LLD
11-14? (which we still support, see Documentation/process/changes.rst;
I guess we don't list LLD explicitly, but it's effectively under the
llvm umbrella there).

IIUC, looks like lld 7.0+ should support SHT_RELR based on looking at
commit 11479daf2f06 ("lld: add experimental support for SHT_RELR sections.")

So we might want to invoke the linker twice, once with the new flag,
and again with the old if we fail the first time?

>
> 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@google.com>
> ---
>  Makefile                      | 2 +-
>  scripts/tools-support-relr.sh | 3 +--
>  2 files changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index a2c310df2145..30c2edc35813 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1113,7 +1113,7 @@ LDFLAGS_vmlinux   += -X
>  endif
>
>  ifeq ($(CONFIG_RELR),y)
> -LDFLAGS_vmlinux        += --pack-dyn-relocs=relr --use-android-relr-tags
> +LDFLAGS_vmlinux        += -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..58c2e8b02ce8 100755
> --- a/scripts/tools-support-relr.sh
> +++ b/scripts/tools-support-relr.sh
> @@ -7,8 +7,7 @@ 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 $tmp_file.o -shared -Bsymbolic -z pack-relative-relocs -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.
> --
> 2.40.0.348.gf938b09366-goog
>
  

On 2023-03-23, Nick Desaulniers wrote:
>Hi Fangrui,
>Thanks for the patches!
>
>On Thu, Mar 23, 2023 at 1:44 PM Fangrui Song <maskray@google.com> wrote:
>>
>> 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, replace --pack-dyn-relocs=relr with -z pack-relative-relocs,
>> which is supported since LLD 15.
>
>Looks like
>commit 4a8de2832a2a ("[ELF] Add -z pack-relative-relocs")
>
>>
>> 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.
>
>Won't this regress support for CONFIG_TOOLS_SUPPORT_RELR for LLD
>11-14? (which we still support, see Documentation/process/changes.rst;
>I guess we don't list LLD explicitly, but it's effectively under the
>llvm umbrella there).
>
>IIUC, looks like lld 7.0+ should support SHT_RELR based on looking at
>commit 11479daf2f06 ("lld: add experimental support for SHT_RELR sections.")
>
>So we might want to invoke the linker twice, once with the new flag,
>and again with the old if we fail the first time?

Yes, I am aware of the increased linker and debugger requirement and was
thinking the CONFIG_RELR=y case with ld.lld<15 did not matter.

Since you raised this, it seems that we should ld.lld<15. How about the following diff?


diff --git a/Makefile b/Makefile
index a2c310df2145..e23a85476d5d 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..355a9b1eb150 100755
--- a/scripts/tools-support-relr.sh
+++ b/scripts/tools-support-relr.sh
@@ -7,8 +7,9 @@ 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 $tmp_file
+# ld.lld before 15 did not support -z pack-relative-relocs.
+$LD $tmp_file.o -shared -Bsymbolic -z pack-relative-relocs -o $tmp_file || \
+	$LD $tmp_file.o -shared -Bsymbolic --pack-dyn-relocs=relr -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.
  

Hi Fangrui,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on masahiroy-kbuild/for-next]
[also build test WARNING on masahiroy-kbuild/fixes linus/master v6.3-rc3 next-20230323]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Fangrui-Song/Makefile-use-z-pack-relative-relocs/20230324-044515
base:   https://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git for-next
patch link:    https://lore.kernel.org/r/20230323204427.3594372-1-maskray%40google.com
patch subject: [PATCH] Makefile: use -z pack-relative-relocs
config: arm64-randconfig-r022-20230322 (https://download.01.org/0day-ci/archive/20230324/202303241443.0sSziFDY-lkp@intel.com/config)
compiler: aarch64-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/8f47a36faf182f96a2bbf4d3b9305fe9a90c5cde
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Fangrui-Song/Makefile-use-z-pack-relative-relocs/20230324-044515
        git checkout 8f47a36faf182f96a2bbf4d3b9305fe9a90c5cde
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=arm64 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=arm64 SHELL=/bin/bash

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
| Link: https://lore.kernel.org/oe-kbuild-all/202303241443.0sSziFDY-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> aarch64-linux-ld: warning: -z pack-relative-relocs ignored
>> aarch64-linux-ld: warning: -z pack-relative-relocs ignored
>> aarch64-linux-ld: warning: -z pack-relative-relocs ignored
  

On Thu, Mar 23, 2023 at 11:51 PM kernel test robot <lkp@intel.com> wrote:
>
> Hi Fangrui,
>
> Thank you for the patch! Perhaps something to improve:
>
> [auto build test WARNING on masahiroy-kbuild/for-next]
> [also build test WARNING on masahiroy-kbuild/fixes linus/master v6.3-rc3 next-20230323]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
>
> url:    https://github.com/intel-lab-lkp/linux/commits/Fangrui-Song/Makefile-use-z-pack-relative-relocs/20230324-044515
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git for-next
> patch link:    https://lore.kernel.org/r/20230323204427.3594372-1-maskray%40google.com
> patch subject: [PATCH] Makefile: use -z pack-relative-relocs
> config: arm64-randconfig-r022-20230322 (https://download.01.org/0day-ci/archive/20230324/202303241443.0sSziFDY-lkp@intel.com/config)
> compiler: aarch64-linux-gcc (GCC) 12.1.0
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://github.com/intel-lab-lkp/linux/commit/8f47a36faf182f96a2bbf4d3b9305fe9a90c5cde
>         git remote add linux-review https://github.com/intel-lab-lkp/linux
>         git fetch --no-tags linux-review Fangrui-Song/Makefile-use-z-pack-relative-relocs/20230324-044515
>         git checkout 8f47a36faf182f96a2bbf4d3b9305fe9a90c5cde
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=arm64 olddefconfig
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=arm64 SHELL=/bin/bash
>
> If you fix the issue, kindly add following tag where applicable
> | Reported-by: kernel test robot <lkp@intel.com>
> | Link: https://lore.kernel.org/oe-kbuild-all/202303241443.0sSziFDY-lkp@intel.com/
>
> All warnings (new ones prefixed by >>):
>
> >> aarch64-linux-ld: warning: -z pack-relative-relocs ignored
> >> aarch64-linux-ld: warning: -z pack-relative-relocs ignored
> >> aarch64-linux-ld: warning: -z pack-relative-relocs ignored
>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests

I forgot to check aarch64-linux-gnu-ld. To address the issue I can use:

# 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