Re: [PATCH] x86/purgatory: Make sure we fail the build if purgatory.ro has missing symbols

[Hans de Goede]

HI,

On 07-10-2019 22:05, Nathan Chancellor wrote:
> On Mon, Oct 07, 2019 at 07:55:46PM +0200, Hans de Goede wrote:
> > Since we link purgatory.ro with -r aka we enable "incremental linking"
> > no checks for unresolved symbols is done while linking purgatory.ro.
> >
> > Changes to the sha256 code has caused the purgatory in 5.4-rc1 to have
> > a missing symbol on memzero_explicit, yet things still happily build.
> >
> > This commit adds an extra check for unresolved symbols by calling ld
> > without -r before running bin2c to generate kexec-purgatory.c.
> >
> > This causes a build of 5.4-rc1 with this patch added to fail as it should:
> >
> >    CHK     arch/x86/purgatory/purgatory.ro
> > ld: arch/x86/purgatory/purgatory.ro: in function `sha256_transform':
> > sha256.c:(.text+0x1c0c): undefined reference to `memzero_explicit'
> > make[2]: *** [arch/x86/purgatory/Makefile:72:
> >      arch/x86/purgatory/kexec-purgatory.c] Error 1
> > make[1]: *** [scripts/Makefile.build:509: arch/x86/purgatory] Error 2
> > make: *** [Makefile:1650: arch/x86] Error 2
> >
> > This will help us catch missing symbols in the purgatory sooner.
> >
> > Note this commit also removes --no-undefined from LDFLAGS_purgatory.ro
> > as that has no effect.
> >
> > Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
> > ---
> >   arch/x86/purgatory/Makefile | 8 +++++++-
> >   1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> > index fb4ee5444379..0da0794ef1f0 100644
> > --- a/arch/x86/purgatory/Makefile
> > +++ b/arch/x86/purgatory/Makefile
> > @@ -14,7 +14,7 @@ $(obj)/sha256.o: $(srctree)/lib/crypto/sha256.c FORCE
> >   
> >   CFLAGS_sha256.o := -D__DISABLE_EXPORTS
> >   
> > -LDFLAGS_purgatory.ro := -e purgatory_start -r --no-undefined -nostdlib -z nodefaultlib
> > +LDFLAGS_purgatory.ro := -e purgatory_start -r -nostdlib -z nodefaultlib
> >   targets += purgatory.ro
> >   
> >   KASAN_SANITIZE	:= n
> > @@ -60,10 +60,16 @@ $(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE
> >   
> >   targets += kexec-purgatory.c
> >   
> > +# Since we link purgatory.ro with -r unresolved symbols are not checked,
> > +# so we check this before generating kexec-purgatory.c instead
> > +quiet_cmd_check_purgatory = CHK     $<
> > +      cmd_check_purgatory = ld -e purgatory_start $<
>
> I think this should be $(LD) -e ... so that using a cross compile prefix
> (like x86_64-linux-) or an alternative linker like ld.lld works properly.

Good point, also the ld command is actually outputting an a.out file
which is also something which we do not want.

I will prepare a new version fixing both.

Regards,

Hans