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Message-ID: <20180312074016.GA1854@dhcp-128-65.nay.redhat.com>
Date: Mon, 12 Mar 2018 15:40:16 +0800
From: Dave Young <dyoung@...hat.com>
To: Philipp Rudo <prudo@...ux.vnet.ibm.com>
Cc: linux-s390@...r.kernel.org,
Heiko Carstens <heiko.carstens@...ibm.com>,
AKASHI Takahiro <takahiro.akashi@...aro.org>,
Michael Ellerman <mpe@...erman.id.au>, x86@...nel.org,
kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Eric Biederman <ebiederm@...ssion.com>,
Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Vivek Goyal <vgoyal@...hat.com>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 00/11] kexec_file: Clean up purgatory load
Hi Philipp,
On 03/09/18 at 03:25pm, Philipp Rudo wrote:
> Hi Dave,
>
> On Fri, 9 Mar 2018 13:19:40 +0800
> Dave Young <dyoung@...hat.com> wrote:
>
> > Hi Philipp,
> > On 02/26/18 at 04:16pm, Philipp Rudo wrote:
> > >
> > > Hi everybody
> > >
> > > following the discussion with Dave and AKASHI, here are the common code
> > > patches extracted from my recent patch set (Add kexec_file_load support to
> > > s390) [1]. The patches were extracted to allow upstream integration together
> > > with AKASHI's common code patches before the arch code gets adjusted to the
> > > new base.
> > >
> > > The reason for this series is to prepare common code for adding
> > > kexec_file_load to s390 as well as cleaning up the mis-use of the sh_offset
> > > field during purgatory load. In detail this series contains:
> > >
> > > Patch #1&2: Minor cleanups/fixes.
> > >
> > > Patch #3-9: Clean up the purgatory load/relocation code. Especially remove
> > > the mis-use of the purgatory_info->sechdrs->sh_offset field, currently
> > > holding a pointer into either kexec_purgatory (ro) or purgatory_buf (rw)
> > > depending on the section. With these patches the section address will be
> > > calculated verbosely and sh_offset will contain the offset of the section
> > > in the stripped purgatory binary (purgatory_buf).
> > >
> > > Patch #10: Allows architectures to set the purgatory load address. This
> > > patch is important for s390 as the kernel and purgatory have to be loaded
> > > to fixed addresses. In current code this is impossible as the purgatory
> > > load is opaque to the architecture.
> > >
> > > Patch #11: Moves x86 purgatories sha implementation to common lib/
> > > directory to allow reuse in other architectures.
> > >
> > > The patches apply to v4.16-rc3. There are no changes compared to [1] (all
> > > requested changes only affected s390 code). Please note that I had to touch
> > > arch code for x86 and power a little. In theory this should not change the
> > > behavior but I don't have a way to test it. Cross-compiling with
> > > defconfig [2] works fine for both.
> > >
> > > Thanks
> > > Philipp
> > >
> > > [1] http://lists.infradead.org/pipermail/kexec/2018-February/019926.html
> > > [2] On x86 with the orc unwinder and stack validation turned off. objtool
> > > SEGFAULTs on s390...
> > >
> > > Philipp Rudo (11):
> > > kexec_file: Silence compile warnings
> > > kexec_file: Remove checks in kexec_purgatory_load
> > > kexec_file: Make purgatory_info->ehdr const
> > > kexec_file: Search symbols in read-only kexec_purgatory
> > > kexec_file: Use read-only sections in arch_kexec_apply_relocations*
> > > kexec_file: Split up __kexec_load_puragory
> > > kexec_file: Simplify kexec_purgatory_setup_sechdrs 1
> > > kexec_file: Simplify kexec_purgatory_setup_sechdrs 2
> > > kexec_file: Remove mis-use of sh_offset field
> > > kexec_file: Allow archs to set purgatory load address
> > > kexec_file: Move purgatories sha256 to common code
> > >
> > > arch/powerpc/kernel/kexec_elf_64.c | 9 +-
> > > arch/x86/kernel/kexec-bzimage64.c | 8 +-
> > > arch/x86/kernel/machine_kexec_64.c | 66 ++---
> > > arch/x86/purgatory/Makefile | 3 +
> > > arch/x86/purgatory/purgatory.c | 2 +-
> > > include/linux/kexec.h | 38 +--
> > > {arch/x86/purgatory => include/linux}/sha256.h | 10 +-
> > > kernel/kexec_file.c | 375 ++++++++++++-------------
> > > {arch/x86/purgatory => lib}/sha256.c | 4 +-
> > > 9 files changed, 244 insertions(+), 271 deletions(-)
> > > rename {arch/x86/purgatory => include/linux}/sha256.h (63%)
> > > rename {arch/x86/purgatory => lib}/sha256.c (99%)
> > >
> > > --
> > > 2.13.5
> > >
> >
> > I did a test on x86, but it failed:
> > [ 15.636489] kexec: Undefined symbol: memcpy
> > [ 15.636496] kexec-bzImage64: Loading purgatory failed
> > [ 33.603356] kexec: Undefined symbol: memcpy
> > [ 33.603362] kexec-bzImage64: Loading purgatory failed
> >
> > I think this relates to the sha256 splitting patch.
>
> I looked into this a little closer and i think i understood what happens.
>
> There is no definition of memcpy in arch/x86/boot/string.c, instead it's defined
> in arch/x86/boot/string.h as __buildin_memcpy (same for memset). Thus by
> switching to linux/string.h there is no more definition for it. Leaving us with
>
> $ readelf -s purgatory.ro
> [...]
> 45: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND memcpy
> [...]
>
> To solve this problem I see two possibilities (example patches are at the end of
> the mail):
>
> 1) Have arch dependent includes in lib/sha256.c
> 2) Add makefile magic so memcpy is defined
>
> With both solutions the resulting purgatory.ro looks good. However both
> solutions aren't perfect. For example in 2) i had too mix the linux/string.h
> header with arch/x86/boot/string.c, because lib/string.c has too many
> dependencies and does not compile in the purgatory. On the other hand having
> arch dependent includes isn't that nice either ...
>
> What's your opinion on this?
Looks like it is a mess, maybe the 1st one is better although it is also
ugly. Ccing Ingo see if he has some idea about this.
>
> Thanks
> Philipp
>
> -----
> Example solution 1
>
> --- a/lib/sha256.c
> +++ b/lib/sha256.c
> @@ -17,9 +17,14 @@
>
> #include <linux/bitops.h>
> #include <linux/sha256.h>
> -#include <linux/string.h>
> #include <asm/byteorder.h>
>
> +#ifdef CONFIG_X86
> +#include "../arch/x86/boot/string.h"
> +#else
> +#include <linux/string.h>
> +#endif /* CONFIG_X86 */
> +
> static inline u32 Ch(u32 x, u32 y, u32 z)
> {
> return z ^ (x & (y ^ z));
>
> -----
> Example solution 2
>
> --- a/arch/x86/purgatory/Makefile
> +++ b/arch/x86/purgatory/Makefile
> @@ -1,7 +1,8 @@
> # SPDX-License-Identifier: GPL-2.0
> OBJECT_FILES_NON_STANDARD := y
>
> -purgatory-y := purgatory.o stack.o setup-x86_$(BITS).o sha256.o entry64.o string.o
> +purgatory-y := purgatory.o stack.o setup-x86_$(BITS).o sha256.o entry64.o \
> + string.o memcpy_$(BITS).o memset_$(BITS).o
>
> targets += $(purgatory-y)
> PURGATORY_OBJS = $(addprefix $(obj)/,$(purgatory-y))
> @@ -9,6 +10,15 @@ PURGATORY_OBJS = $(addprefix $(obj)/,$(purgatory-y))
> $(obj)/sha256.o: $(srctree)/lib/sha256.c
> $(call if_changed_rule,cc_o_c)
>
> +$(obj)/string.o: $(srctree)/arch/x86/boot/string.c
> + $(call if_changed_rule,cc_o_c)
> +
> +$(obj)/memset_$(BITS).o: $(srctree)/arch/x86/lib/memset_$(BITS).S
> + $(call if_changed_rule,as_o_S)
> +
> +$(obj)/memcpy_$(BITS).o: $(srctree)/arch/x86/lib/memcpy_$(BITS).S
> + $(call if_changed_rule,as_o_S)
> +
> LDFLAGS_purgatory.ro := -e purgatory_start -r --no-undefined -nostdlib -z nodefaultlib
> targets += purgatory.ro
>
>
Thanks
Dave
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