[RFC 0/1] s390/purgatory: Make sure we fail the build if purgatory has missing symbols

[RFC 0/1] s390/purgatory: Make sure we fail the build if purgatory has missing symbols

[Hans de Goede]

Hi s390 maintainers,

This patch mirrors a similar patch for x86, but it has been untested
because I do not have a mainframe to compile on :)

In 5.4-rc1 the 2 different sha256 implementations for the purgatory resp.
for crypto/sha256_generic.c have been consolidated into 1 single shared
implementation under lib/crypto/sha256.c .

At least on x86 this was causing silent corruption of the purgatory due
to a missing memzero_explicit symbol in the purgatory string.c/.o file.

With the x86 equivalent of this patch applied a x86 build of 5.4-rc1 now
correctly fails:

  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

It would be great if the s390 maintainers can test this equivalent patch
on s390.

As for fixing the missing memzero_explicit symbol, we are currently
discussing making memzero_explicit a static inline wrapper of memset
in string.h, so that we do not need to implement it in multiple places.

This discussion is Cc-ed to the generic linux-kernel@vger.kernel.org list,
it is happening in the
"[PATCH v2 5.4 regression fix] x86/boot: Provide memzero_explicit" thread.

Regards,

Hans

[RFC] s390/purgatory: Make sure we fail the build if purgatory has missing symbols

[Hans de Goede]

Since we link purgatory with -r aka we enable "incremental linking"
no checks for unresolved symbols are done while linking the purgatory.

This commit adds an extra check for unresolved symbols by calling ld
without -r before running objcopy to generate purgatory.ro.

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/s390/purgatory/Makefile | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/s390/purgatory/Makefile b/arch/s390/purgatory/Makefile
index bc0d7a0d0394..d5405fe7b2e2 100644
--- a/arch/s390/purgatory/Makefile
+++ b/arch/s390/purgatory/Makefile
@@ -26,15 +26,21 @@ KBUILD_CFLAGS += $(CLANG_FLAGS)
 KBUILD_CFLAGS += $(call cc-option,-fno-PIE)
 KBUILD_AFLAGS := $(filter-out -DCC_USING_EXPOLINE,$(KBUILD_AFLAGS))
 
-LDFLAGS_purgatory := -r --no-undefined -nostdlib -z nodefaultlib -T
+LDFLAGS_purgatory := -r -nostdlib -z nodefaultlib -T
 $(obj)/purgatory: $(obj)/purgatory.lds $(PURGATORY_OBJS) FORCE
 		$(call if_changed,ld)
 
+# Since we link purgatory with -r unresolved symbols are not checked,
+# so we check this before generating purgatory.ro instead
+quiet_cmd_check_purgatory = CHK     $<
+      cmd_check_purgatory = ld -e purgatory_start $<
+
 OBJCOPYFLAGS_purgatory.ro := -O elf64-s390
 OBJCOPYFLAGS_purgatory.ro += --remove-section='*debug*'
 OBJCOPYFLAGS_purgatory.ro += --remove-section='.comment'
 OBJCOPYFLAGS_purgatory.ro += --remove-section='.note.*'
 $(obj)/purgatory.ro: $(obj)/purgatory FORCE
+		$(call if_changed,check_purgatory)
 		$(call if_changed,objcopy)
 
 $(obj)/kexec-purgatory.o: $(obj)/kexec-purgatory.S $(obj)/purgatory.ro FORCE
-- 
2.23.0