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SubjectRe: [PATCH 4.14 09/69] x86: vdso: Use $LD instead of $CC to link
Date
On Mon, 2019-04-15 at 20:58 +0200, Greg Kroah-Hartman wrote:
> commit 379d98ddf41344273d9718556f761420f4dc80b3 upstream.
>

Hi,

With this patch in 4.14.112 build-id is now missing in vdso32.so:

$ file arch/x86/entry/vdso/vdso*so*
arch/x86/entry/vdso/vdso32.so: ELF 32-bit LSB pie executable, Intel
80386, version 1 (SYSV), dynamically linked, stripped
arch/x86/entry/vdso/vdso32.so.dbg: ELF 32-bit LSB pie executable, Intel
80386, version 1 (SYSV), dynamically linked, with debug_info, not
stripped
arch/x86/entry/vdso/vdso64.so: ELF 64-bit LSB pie executable, x86-
64, version 1 (SYSV), dynamically linked,
BuildID[sha1]=d80730a5b561a3161e488a369d1c76c250b584b4, stripped
arch/x86/entry/vdso/vdso64.so.dbg: ELF 64-bit LSB pie executable, x86-
64, version 1 (SYSV), dynamically linked,
BuildID[sha1]=d80730a5b561a3161e488a369d1c76c250b584b4, with
debug_info, not stripped


Based on quick check, "$(call ld-option, --build-id)" fails due to some
32/64 bit mismatch, so the --build-id linker flag is not used when
linking vdso32.so

Perhaps scripts/Kbuild.include is missing some change in 4.14.y to make
this work properly.

-Tommi

> The vdso{32,64}.so can fail to link with CC=clang when clang tries to
> find
> a suitable GCC toolchain to link these libraries with.
>
> /usr/bin/ld: arch/x86/entry/vdso/vclock_gettime.o:
> access beyond end of merged section (782)
>
> This happens because the host environment leaked into the cross
> compiler
> environment due to the way clang searches for suitable GCC
> toolchains.
>
> Clang is a retargetable compiler, and each invocation of it must
> provide
> --target=<something> --gcc-toolchain=<something> to allow it to find
> the
> correct binutils for cross compilation. These flags had been added to
> KBUILD_CFLAGS, but the vdso code uses CC and not KBUILD_CFLAGS (for
> various
> reasons) which breaks clang's ability to find the correct linker when
> cross
> compiling.
>
> Most of the time this goes unnoticed because the host linker is new
> enough
> to work anyway, or is incompatible and skipped, but this cannot be
> reliably
> assumed.
>
> This change alters the vdso makefile to just use LD directly, which
> bypasses clang and thus the searching problem. The makefile will just
> use
> ${CROSS_COMPILE}ld instead, which is always what we want. This
> matches the
> method used to link vmlinux.
>
> This drops references to DISABLE_LTO; this option doesn't seem to be
> set
> anywhere, and not knowing what its possible values are, it's not
> clear how
> to convert it from CC to LD flag.
>
> Signed-off-by: Alistair Strachan <astrachan@google.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Acked-by: Andy Lutomirski <luto@kernel.org>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: kernel-team@android.com
> Cc: joel@joelfernandes.org
> Cc: Andi Kleen <andi.kleen@intel.com>
> Link:
> https://lkml.kernel.org/r/20180803173931.117515-1-astrachan@google.com
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> arch/x86/entry/vdso/Makefile | 22 +++++++++-------------
> 1 file changed, 9 insertions(+), 13 deletions(-)
>
> diff --git a/arch/x86/entry/vdso/Makefile
> b/arch/x86/entry/vdso/Makefile
> index 0a550dc5c525..0defcc939ab4 100644
> --- a/arch/x86/entry/vdso/Makefile
> +++ b/arch/x86/entry/vdso/Makefile
> @@ -48,10 +48,8 @@ targets += $(vdso_img_sodbg)
>
> export CPPFLAGS_vdso.lds += -P -C
>
> -VDSO_LDFLAGS_vdso.lds = -m64 -Wl,-soname=linux-vdso.so.1 \
> - -Wl,--no-undefined \
> - -Wl,-z,max-page-size=4096 -Wl,-z,common-page-
> size=4096 \
> - $(DISABLE_LTO)
> +VDSO_LDFLAGS_vdso.lds = -m elf_x86_64 -soname linux-vdso.so.1 --no-
> undefined \
> + -z max-page-size=4096 -z common-page-size=4096
>
> $(obj)/vdso64.so.dbg: $(src)/vdso.lds $(vobjs) FORCE
> $(call if_changed,vdso)
> @@ -103,10 +101,8 @@ CFLAGS_REMOVE_vvar.o = -pg
> #
>
> CPPFLAGS_vdsox32.lds = $(CPPFLAGS_vdso.lds)
> -VDSO_LDFLAGS_vdsox32.lds = -Wl,-m,elf32_x86_64 \
> - -Wl,-soname=linux-vdso.so.1 \
> - -Wl,-z,max-page-size=4096 \
> - -Wl,-z,common-page-size=4096
> +VDSO_LDFLAGS_vdsox32.lds = -m elf32_x86_64 -soname linux-vdso.so.1 \
> + -z max-page-size=4096 -z common-page-
> size=4096
>
> # 64-bit objects to re-brand as x32
> vobjs64-for-x32 := $(filter-out $(vobjs-nox32),$(vobjs-y))
> @@ -134,7 +130,7 @@ $(obj)/vdsox32.so.dbg: $(src)/vdsox32.lds
> $(vobjx32s) FORCE
> $(call if_changed,vdso)
>
> CPPFLAGS_vdso32.lds = $(CPPFLAGS_vdso.lds)
> -VDSO_LDFLAGS_vdso32.lds = -m32 -Wl,-m,elf_i386 -Wl,-soname=linux-
> gate.so.1
> +VDSO_LDFLAGS_vdso32.lds = -m elf_i386 -soname linux-gate.so.1
>
> # This makes sure the $(obj) subdirectory exists even though vdso32/
> # is not a kbuild sub-make subdirectory.
> @@ -180,13 +176,13 @@ $(obj)/vdso32.so.dbg: FORCE \
> # The DSO images are built using a special linker script.
> #
> quiet_cmd_vdso = VDSO $@
> - cmd_vdso = $(CC) -nostdlib -o $@ \
> + cmd_vdso = $(LD) -nostdlib -o $@ \
> $(VDSO_LDFLAGS) $(VDSO_LDFLAGS_$(filter
> %.lds,$(^F))) \
> - -Wl,-T,$(filter %.lds,$^) $(filter %.o,$^) && \
> + -T $(filter %.lds,$^) $(filter %.o,$^) && \
> sh $(srctree)/$(src)/checkundef.sh '$(NM)' '$@'
>
> -VDSO_LDFLAGS = -fPIC -shared $(call cc-ldoption, -Wl$(comma)--hash-
> style=both) \
> - $(call cc-ldoption, -Wl$(comma)--build-id) -Wl,-Bsymbolic
> $(LTO_CFLAGS)
> +VDSO_LDFLAGS = -shared $(call ld-option, --hash-style=both) \
> + $(call ld-option, --build-id) -Bsymbolic
> GCOV_PROFILE := n
>
> #

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