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

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

[Hans de Goede]

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@redhat.com>
---
 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 $<
+
 quiet_cmd_bin2c = BIN2C   $@
       cmd_bin2c = $(objtree)/scripts/bin2c kexec_purgatory < $< > $@
 
 $(obj)/kexec-purgatory.c: $(obj)/purgatory.ro FORCE
+	$(call if_changed,check_purgatory)
 	$(call if_changed,bin2c)
 
 obj-$(CONFIG_KEXEC_FILE)	+= kexec-purgatory.o
-- 
2.23.0

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

[Nathan Chancellor]

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@redhat.com>
> ---
>  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.

> +
>  quiet_cmd_bin2c = BIN2C   $@
>        cmd_bin2c = $(objtree)/scripts/bin2c kexec_purgatory < $< > $@
>  
>  $(obj)/kexec-purgatory.c: $(obj)/purgatory.ro FORCE
> +	$(call if_changed,check_purgatory)
>  	$(call if_changed,bin2c)
>  
>  obj-$(CONFIG_KEXEC_FILE)	+= kexec-purgatory.o
> -- 
> 2.23.0
> 

Cheers,
Nathan

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@redhat.com>
>> ---
>>   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

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

[Arvind Sankar]

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@redhat.com>
> >> ---
> >>   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?

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@redhat.com>
>>>> ---
>>>>    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