Re: [PATCH] xen: add support for crash dump analysis with xen.efi

[Juergen Gross <jgross@xxxxxxxx>]

On 24.04.23 14:01, Jan Beulich wrote:
> On 21.04.2023 15:59, Juergen Gross wrote:
> > Today it is not possible to analyse crash dumps of a system in
> > hypervisor mode when it had been booted via EFI, as the crash utility
> > doesn't understand the file format of xen.efi.
> >
> > This can easily be solved by creating an ELF file from xen.efi via
> > objcopy. Using that file as name list for crash enables the user to
> > analyse the dump in hypervisor mode.
> >
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > ---
> >   xen/Kconfig.debug     | 5 ++++-
> >   xen/Makefile          | 4 ++++
> >   xen/arch/x86/Makefile | 3 +++
> >   3 files changed, 11 insertions(+), 1 deletion(-)
> >
> > diff --git a/xen/Kconfig.debug b/xen/Kconfig.debug
> > index 94e818ee09..4aec0fd3aa 100644
> > --- a/xen/Kconfig.debug
> > +++ b/xen/Kconfig.debug
> > @@ -138,6 +138,9 @@ config DEBUG_INFO
> >           the EFI boot partition (look for "INSTALL_EFI_STRIP" in
> >           docs/misc/efi.pandoc for more information - when not using
> >           "make install-xen" for installing xen.efi, stripping needs to be
> > -         done outside the Xen build environment).
> > +         done outside the Xen build environment). Note that stripping
> > +         xen.efi using "INSTALL_EFI_STRIP" will disable the building of
> > +         xen.efi.elf, which is needed for "crash" dump analysis of systems
> > +         booted via EFI.
> I'm afraid I don't understand this: INSTALL_EFI_STRIP only affects what
> may (optionally) be placed on the EFI partition. The normally installed
> xen.efi should be unaffected by this; an intermediate xen.efi.stripped
> is created instead.
Oh, obviously I misinterpreted something. I'll drop this hunk.

> > --- a/xen/Makefile
> > +++ b/xen/Makefile
> > @@ -505,6 +505,9 @@ _install: $(TARGET)$(CONFIG_XEN_INSTALL_SUFFIX)
> >                 if [ -e $(TARGET).efi.map ]; then \
> >                         $(INSTALL_DATA) $(TARGET).efi.map 
> > $(D)$(DEBUG_DIR)/$(T)-$(XEN_FULLVERSION).efi.map; \
> >                 fi; \
> > +               if [ -e $(TARGET).efi.elf ]; then \
> > +                       $(INSTALL_DATA) $(TARGET).efi.elf 
> > $(D)$(DEBUG_DIR)/$(T)-$(XEN_FULLVERSION).efi.elf; \
> > +               fi; \
> To avoid the risk of the two going out of sync (as also to limit
> redundancy), could you wrap the earlier "if" in a "for x in map elf;
> do ...; done" loop?
Sure, will do.

> > --- a/xen/arch/x86/Makefile
> > +++ b/xen/arch/x86/Makefile
> > @@ -224,6 +224,9 @@ endif
> >         $(MAKE) $(build)=$(@D) .$(@F).1r.o .$(@F).1s.o
> >         $(LD) $(call EFI_LDFLAGS,$(VIRT_BASE)) -T $(obj)/efi.lds -N $< \
> >               $(@D)/.$(@F).1r.o $(@D)/.$(@F).1s.o $(orphan-handling-y) 
> > $(note_file_option) -o $@
> > +ifeq ($(CONFIG_DEBUG_INFO),y)
> > +       $(if $(filter --strip-debug,$(EFI_LDFLAGS)),,$(OBJCOPY) -O elf64-x86-64 
> > $@ $@.elf)
> > +endif
> >         $(NM) -pa --format=sysv $(@D)/$(@F) \
> >                 | $(objtree)/tools/symbols --all-symbols --xensyms --sysv --sort 
> > >$(@D)/$(@F).map
> >         rm -f $(@D)/.$(@F).[0-9]* $(@D)/..$(@F).[0-9]*
> Personally I think that - in case of build problems - having the map file
> created is more important (and less likely to fail) than the ELF one, so
> I'd prefer if the two steps could be ordered the other way around.
Fine with me.

> Further I vaguely recall possible issues with entirely blank make rule
> lines. Plus having some trace of the command in a verbose log perhaps
> also wouldn't hurt. IOW maybe better add another use of the colon command
> here (we already have some, at least through $(MKRELOC)):
>
> ifeq ($(CONFIG_DEBUG_INFO),y)
>         $(if $(filter --strip-debug,$(EFI_LDFLAGS)),:)$(OBJCOPY) -O 
> elf64-x86-64 $@ $@.elf
> endif
>
> ?
Okay.

> Finally - do you really need to copy all the non-debug sections as well?
> Might --only-keep-debug be helpful here (provided it works for a PE/COFF
> -> ELF copy operation; it looks to do so in my simple experiments)?
No, doesn't work (objcopy does, but not crash with that file):

  crash: xen.efi.elf: no text and data contents


Juergen

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