Re: [PATCH 00/11] kexec_file: Clean up purgatory load

[Dave Young <dyoung@redhat.com>]

On 03/12/18 at 03:40pm, Dave Young wrote:
> 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@redhat.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. 

Maybe something like below is better if no other idea:

diff --git a/arch/x86/boot/string_builtin.c b/arch/x86/boot/string_builtin.c
new file mode 100644
index 000000000000..9099f949fb41
--- /dev/null
+++ b/arch/x86/boot/string_builtin.c
@@ -0,0 +1,11 @@
+#include <linux/types.h>
+
+void *memcpy(void *dst, const void *src, size_t len)
+{
+	return __builtin_memcpy(dst, src, len);
+}
+
+void *memset(void *dst, int c, size_t len)
+{
+	return __builtin_memset(dst, c, len);
+}
diff --git a/arch/x86/purgatory/string.c b/arch/x86/purgatory/string.c
index d886b1fa36f0..e12c78fcd59f 100644
--- a/arch/x86/purgatory/string.c
+++ b/arch/x86/purgatory/string.c
@@ -11,3 +11,4 @@
  */
 
 #include "../boot/string.c"
+#include "../boot/string_builtin.c"

> 
> > 
> > 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