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

From: Hans de Goede
Date: Thu Dec 12 2019 - 15:50:18 EST

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>
Changes in v3:
- Add a .gitignore file with purgatory.chk listed in it

Changes in v2:
- Using 2 if_changed lines under a single rule does not work, then
1 of the 2 will always execute each build.
Instead add a new (unused) purgatory.chk intermediate which gets
linked from purgatory.ro without -r to do the missing symbols check
- This also fixes the check generating an a.out file (oops)
arch/x86/purgatory/.gitignore | 1 +
arch/x86/purgatory/Makefile | 13 ++++++++++---
2 files changed, 11 insertions(+), 3 deletions(-)
create mode 100644 arch/x86/purgatory/.gitignore

diff --git a/arch/x86/purgatory/.gitignore b/arch/x86/purgatory/.gitignore
new file mode 100644
index 000000000000..d2be1500671d
--- /dev/null
+++ b/arch/x86/purgatory/.gitignore
@@ -0,0 +1 @@
diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index fb4ee5444379..5bb58247699d 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -14,8 +14,12 @@ $(obj)/sha256.o: $(srctree)/lib/crypto/sha256.c FORCE


-LDFLAGS_purgatory.ro := -e purgatory_start -r --no-undefined -nostdlib -z nodefaultlib
-targets += purgatory.ro
+# Since we link purgatory.ro with -r unresolved symbols are not checked, so we
+# also link a purgatory.chk binary without -r to check for unresolved symbols.
+PURGATORY_LDFLAGS := -e purgatory_start -nostdlib -z nodefaultlib
+LDFLAGS_purgatory.ro := -r $(PURGATORY_LDFLAGS)
+LDFLAGS_purgatory.chk := $(PURGATORY_LDFLAGS)
+targets += purgatory.ro purgatory.chk

@@ -58,12 +62,15 @@ CFLAGS_string.o += $(PURGATORY_CFLAGS)
$(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE
$(call if_changed,ld)

+$(obj)/purgatory.chk: $(obj)/purgatory.ro FORCE
+ $(call if_changed,ld)
targets += kexec-purgatory.c

quiet_cmd_bin2c = BIN2C $@
cmd_bin2c = $(objtree)/scripts/bin2c kexec_purgatory < $< > $@

-$(obj)/kexec-purgatory.c: $(obj)/purgatory.ro FORCE
+$(obj)/kexec-purgatory.c: $(obj)/purgatory.ro $(obj)/purgatory.chk FORCE
$(call if_changed,bin2c)

obj-$(CONFIG_KEXEC_FILE) += kexec-purgatory.o