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

[Hans de Goede]

HI,

On 07-10-2019 23:52, Arvind Sankar wrote:
> On Mon, Oct 07, 2019 at 10:31:49PM +0200, Hans de Goede wrote:
> > 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
>
> We could just use $(NM) -u, right?

That would require wrapping it in some shell code like this (untested):

SHOULD_BE_EMPTY=$(nm -u purgatory.ro); if [ "$SHOULD_BE_EMPTY" == "" ]; then true; else false; fi

And then escaping the $ in there and in injecting $(NM) into it, IMHO
it is easier to just do:

$(LD) $PURGATORY_LDFLAGS) purgatory.ro -o /dev/null

Also it seems better to actually use the linker for this test then usig an other
tool which may have subtly different semantics.

Regards,

Hans