Re: [PATCH v2] vdso: Improve cmd_vdso_check to check all dynamic relocations

[Vincenzo Frascino]

Hi Fangrui,

Apologize for the delay, I totally missed that you had a new version of your
patch since it was threaded with the old one.

On 12/21/22 23:51, Fangrui Song wrote:
> The actual intention is that no dynamic relocation exists. However, some
> GNU ld ports produce unneeded R_*_NONE. (If a port fails to determine
> the exact .rel[a].dyn size, the trailing zeros become R_*_NONE
> relocations. E.g. ld's powerpc port recently fixed
> https://sourceware.org/bugzilla/show_bug.cgi?id=29540) R_*_NONE are
> generally no-op in the dynamic loaders. So just ignore them.
> 
> With the change, we can remove ARCH_REL_TYPE_ABS. ARCH_REL_TYPE_ABS is a
> bit misnomer as ports may check RELAVETIVE/GLOB_DAT/JUMP_SLOT which are
> not called "absolute relocations". (The patch is motivated by the arm64
> port missing R_AARCH64_RELATIVE.)

It makes sense to update the name, it started as "absolute relocations" but then
it evolved into something else.

A part that, did you perform any testing with the generated vDSO libraries?

> 
> Signed-off-by: Fangrui Song <maskray@xxxxxxxxxx>
> Reviewed-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> ---
> Change from v1:
> * rebase after 8ac3b5cd3e0521d92f9755e90d140382fc292510 (lib/vdso: use "grep -E"
> instead of "egrep")
> * change the commit message to mention an example GNU ld bug; no longer say the
> patch fixes a deprecated egrep use
> ---
>  arch/arm/vdso/Makefile            |  3 ---
>  arch/arm64/kernel/vdso/Makefile   |  3 ---
>  arch/arm64/kernel/vdso32/Makefile |  3 ---
>  arch/csky/kernel/vdso/Makefile    |  3 ---
>  arch/loongarch/vdso/Makefile      |  3 ---
>  arch/mips/vdso/Makefile           |  3 ---
>  arch/powerpc/kernel/vdso/Makefile |  1 -
>  arch/riscv/kernel/vdso/Makefile   |  3 ---
>  arch/s390/kernel/vdso32/Makefile  |  2 --
>  arch/s390/kernel/vdso64/Makefile  |  2 --
>  arch/x86/entry/vdso/Makefile      |  4 ----
>  lib/vdso/Makefile                 | 13 ++++---------
>  12 files changed, 4 insertions(+), 39 deletions(-)
> 
> diff --git a/arch/arm/vdso/Makefile b/arch/arm/vdso/Makefile
> index a7ec06ce3785..e58197bba776 100644
> --- a/arch/arm/vdso/Makefile
> +++ b/arch/arm/vdso/Makefile
> @@ -1,8 +1,5 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
> -# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
> -# the inclusion of generic Makefile.
> -ARCH_REL_TYPE_ABS := R_ARM_JUMP_SLOT|R_ARM_GLOB_DAT|R_ARM_ABS32

I would still add a comment here to say why we are including the generic
Makefile to prevent that it gets accidentally removed (similar thing for every
architecture touched by this patch).

With that:

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> # for vDSO, aarch64
Tested-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> # for aarch64

>  include $(srctree)/lib/vdso/Makefile
>  
>  hostprogs := vdsomunge
> diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
> index beaf9586338f..1f2427b13410 100644
> --- a/arch/arm64/kernel/vdso/Makefile
> +++ b/arch/arm64/kernel/vdso/Makefile
> @@ -6,9 +6,6 @@
>  # Heavily based on the vDSO Makefiles for other archs.
>  #
>  
> -# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
> -# the inclusion of generic Makefile.
> -ARCH_REL_TYPE_ABS := R_AARCH64_JUMP_SLOT|R_AARCH64_GLOB_DAT|R_AARCH64_ABS64
>  include $(srctree)/lib/vdso/Makefile
>  
>  obj-vdso := vgettimeofday.o note.o sigreturn.o
> diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
> index f59bd1a4ead6..d014162c5c71 100644
> --- a/arch/arm64/kernel/vdso32/Makefile
> +++ b/arch/arm64/kernel/vdso32/Makefile
> @@ -3,9 +3,6 @@
>  # Makefile for vdso32
>  #
>  
> -# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
> -# the inclusion of generic Makefile.
> -ARCH_REL_TYPE_ABS := R_ARM_JUMP_SLOT|R_ARM_GLOB_DAT|R_ARM_ABS32
>  include $(srctree)/lib/vdso/Makefile
>  
>  # Same as cc-*option, but using CC_COMPAT instead of CC
> diff --git a/arch/csky/kernel/vdso/Makefile b/arch/csky/kernel/vdso/Makefile
> index 0b6909f10667..86c8c4de1b0f 100644
> --- a/arch/csky/kernel/vdso/Makefile
> +++ b/arch/csky/kernel/vdso/Makefile
> @@ -1,8 +1,5 @@
>  # SPDX-License-Identifier: GPL-2.0-only
>  
> -# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
> -# the inclusion of generic Makefile.
> -ARCH_REL_TYPE_ABS := R_CKCORE_ADDR32|R_CKCORE_JUMP_SLOT
>  include $(srctree)/lib/vdso/Makefile
>  
>  # Symbols present in the vdso
> diff --git a/arch/loongarch/vdso/Makefile b/arch/loongarch/vdso/Makefile
> index d89e2ac75f7b..1b2e0f149f55 100644
> --- a/arch/loongarch/vdso/Makefile
> +++ b/arch/loongarch/vdso/Makefile
> @@ -1,9 +1,6 @@
>  # SPDX-License-Identifier: GPL-2.0
>  # Objects to go into the VDSO.
>  
> -# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
> -# the inclusion of generic Makefile.
> -ARCH_REL_TYPE_ABS := R_LARCH_32|R_LARCH_64|R_LARCH_MARK_LA|R_LARCH_JUMP_SLOT
>  include $(srctree)/lib/vdso/Makefile
>  
>  obj-vdso-y := elf.o vgetcpu.o vgettimeofday.o sigreturn.o
> diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
> index 1f7d5c6c10b0..c060f3596304 100644
> --- a/arch/mips/vdso/Makefile
> +++ b/arch/mips/vdso/Makefile
> @@ -4,9 +4,6 @@
>  # Sanitizer runtimes are unavailable and cannot be linked here.
>   KCSAN_SANITIZE            := n
>  
> -# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
> -# the inclusion of generic Makefile.
> -ARCH_REL_TYPE_ABS := R_MIPS_JUMP_SLOT|R_MIPS_GLOB_DAT
>  include $(srctree)/lib/vdso/Makefile
>  
>  obj-vdso-y := elf.o vgettimeofday.o sigreturn.o
> diff --git a/arch/powerpc/kernel/vdso/Makefile b/arch/powerpc/kernel/vdso/Makefile
> index 6a977b0d8ffc..83c347e9136f 100644
> --- a/arch/powerpc/kernel/vdso/Makefile
> +++ b/arch/powerpc/kernel/vdso/Makefile
> @@ -2,7 +2,6 @@
>  
>  # List of files in the vdso, has to be asm only for now
>  
> -ARCH_REL_TYPE_ABS :=
> R_PPC_JUMP_SLOT|R_PPC_GLOB_DAT|R_PPC_ADDR32|R_PPC_ADDR24|R_PPC_ADDR16|R_PPC_ADDR16_LO|R_PPC_ADDR16_HI|R_PPC_ADDR16_HA|R_PPC_ADDR14|R_PPC_ADDR14_BRTAKEN|R_PPC_ADDR14_BRNTAKEN|R_PPC_REL24
>  include $(srctree)/lib/vdso/Makefile
>  
>  obj-vdso32 = sigtramp32-32.o gettimeofday-32.o datapage-32.o cacheflush-32.o
> note-32.o getcpu-32.o
> diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
> index 06e6b27f3bcc..d85c37e11b21 100644
> --- a/arch/riscv/kernel/vdso/Makefile
> +++ b/arch/riscv/kernel/vdso/Makefile
> @@ -1,9 +1,6 @@
>  # SPDX-License-Identifier: GPL-2.0-only
>  # Copied from arch/tile/kernel/vdso/Makefile
>  
> -# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
> -# the inclusion of generic Makefile.
> -ARCH_REL_TYPE_ABS := R_RISCV_32|R_RISCV_64|R_RISCV_JUMP_SLOT
>  include $(srctree)/lib/vdso/Makefile
>  # Symbols present in the vdso
>  vdso-syms  = rt_sigreturn
> diff --git a/arch/s390/kernel/vdso32/Makefile b/arch/s390/kernel/vdso32/Makefile
> index 245bddfe9bc0..e795fdbbf484 100644
> --- a/arch/s390/kernel/vdso32/Makefile
> +++ b/arch/s390/kernel/vdso32/Makefile
> @@ -2,8 +2,6 @@
>  # List of files in the vdso
>  
>  KCOV_INSTRUMENT := n
> -ARCH_REL_TYPE_ABS := R_390_COPY|R_390_GLOB_DAT|R_390_JMP_SLOT|R_390_RELATIVE
> -ARCH_REL_TYPE_ABS += R_390_GOT|R_390_PLT
>  
>  include $(srctree)/lib/vdso/Makefile
>  obj-vdso32 = vdso_user_wrapper-32.o note-32.o
> diff --git a/arch/s390/kernel/vdso64/Makefile b/arch/s390/kernel/vdso64/Makefile
> index 9e2b95a222a9..47dbbfdfad68 100644
> --- a/arch/s390/kernel/vdso64/Makefile
> +++ b/arch/s390/kernel/vdso64/Makefile
> @@ -2,8 +2,6 @@
>  # List of files in the vdso
>  
>  KCOV_INSTRUMENT := n
> -ARCH_REL_TYPE_ABS := R_390_COPY|R_390_GLOB_DAT|R_390_JMP_SLOT|R_390_RELATIVE
> -ARCH_REL_TYPE_ABS += R_390_GOT|R_390_PLT
>  
>  include $(srctree)/lib/vdso/Makefile
>  obj-vdso64 = vdso_user_wrapper.o note.o
> diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> index 838613ac15b8..b292c24acb8e 100644
> --- a/arch/x86/entry/vdso/Makefile
> +++ b/arch/x86/entry/vdso/Makefile
> @@ -3,10 +3,6 @@
>  # Building vDSO images for x86.
>  #
>  
> -# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
> -# the inclusion of generic Makefile.
> -ARCH_REL_TYPE_ABS := R_X86_64_JUMP_SLOT|R_X86_64_GLOB_DAT|R_X86_64_RELATIVE|
> -ARCH_REL_TYPE_ABS += R_386_GLOB_DAT|R_386_JMP_SLOT|R_386_RELATIVE
>  include $(srctree)/lib/vdso/Makefile
>  
>  # Sanitizer runtimes are unavailable and cannot be linked here.
> diff --git a/lib/vdso/Makefile b/lib/vdso/Makefile
> index e814061d6aa0..9f031eafc465 100644
> --- a/lib/vdso/Makefile
> +++ b/lib/vdso/Makefile
> @@ -5,18 +5,13 @@ GENERIC_VDSO_DIR := $(dir $(GENERIC_VDSO_MK_PATH))
>  
>  c-gettimeofday-$(CONFIG_GENERIC_GETTIMEOFDAY) := $(addprefix
> $(GENERIC_VDSO_DIR), gettimeofday.c)
>  
> -# This cmd checks that the vdso library does not contain absolute relocation
> +# This cmd checks that the vdso library does not contain dynamic relocations.
>  # It has to be called after the linking of the vdso library and requires it
>  # as a parameter.
>  #
> -# $(ARCH_REL_TYPE_ABS) is defined in the arch specific makefile and corresponds
> -# to the absolute relocation types printed by "objdump -R" and accepted by the
> -# dynamic linker.
> -ifndef ARCH_REL_TYPE_ABS
> -$(error ARCH_REL_TYPE_ABS is not set)
> -endif
> -
> +# As a workaround for some GNU ld ports which produce unneeded R_*_NONE
> +# dynamic relocations, ignore R_*_NONE.
>  quiet_cmd_vdso_check = VDSOCHK $@
> -      cmd_vdso_check = if $(OBJDUMP) -R $@ | grep -E -h "$(ARCH_REL_TYPE_ABS)"; \
> +      cmd_vdso_check = if $(READELF) -rW $@ | grep -v _NONE | grep -q " R_\w*_"; \
>                 then (echo >&2 "$@: dynamic relocations are not supported"; \
>                   rm -f $@; /bin/false); fi

-- 
Regards,
Vincenzo