linux-kernel - [PATCH 1/1] x86/purgatory: Change compiler flags to avoid relocation errors.

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Date:   Wed, 4 Sep 2019 16:45:05 -0500
From:   Steve Wahl <steve.wahl@....com>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com, vaibhavrustagi@...gle.com,
        russ.anderson@....com, dimitri.sivanich@....com,
        mike.travis@....com
Subject: [PATCH 1/1] x86/purgatory: Change compiler flags to avoid relocation
 errors.

The last change to this Makefile caused relocation errors when loading
a kdump kernel.  This change restores the appropriate flags, without
reverting to the former practice of resetting KBUILD_CFLAGS.

Signed-off-by: Steve Wahl <steve.wahl@....com>
---
 arch/x86/purgatory/Makefile | 35 +++++++++++++++++++----------------
 1 file changed, 19 insertions(+), 16 deletions(-)

diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index 8901a1f89cf5..9f0bfef1f5db 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -18,37 +18,40 @@ targets += purgatory.ro
 KASAN_SANITIZE	:= n
 KCOV_INSTRUMENT := n
 
+# These are adjustments to the compiler flags used for objects that
+# make up the standalone porgatory.ro
+
+PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
+PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss
+
 # Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
 # in turn leaves some undefined symbols like __fentry__ in purgatory and not
 # sure how to relocate those.
 ifdef CONFIG_FUNCTION_TRACER
-CFLAGS_REMOVE_sha256.o		+= $(CC_FLAGS_FTRACE)
-CFLAGS_REMOVE_purgatory.o	+= $(CC_FLAGS_FTRACE)
-CFLAGS_REMOVE_string.o		+= $(CC_FLAGS_FTRACE)
-CFLAGS_REMOVE_kexec-purgatory.o	+= $(CC_FLAGS_FTRACE)
+PURGATORY_CFLAGS_REMOVE		+= $(CC_FLAGS_FTRACE)
 endif
 
 ifdef CONFIG_STACKPROTECTOR
-CFLAGS_REMOVE_sha256.o		+= -fstack-protector
-CFLAGS_REMOVE_purgatory.o	+= -fstack-protector
-CFLAGS_REMOVE_string.o		+= -fstack-protector
-CFLAGS_REMOVE_kexec-purgatory.o	+= -fstack-protector
+PURGATORY_CFLAGS_REMOVE		+= -fstack-protector
 endif
 
 ifdef CONFIG_STACKPROTECTOR_STRONG
-CFLAGS_REMOVE_sha256.o		+= -fstack-protector-strong
-CFLAGS_REMOVE_purgatory.o	+= -fstack-protector-strong
-CFLAGS_REMOVE_string.o		+= -fstack-protector-strong
-CFLAGS_REMOVE_kexec-purgatory.o	+= -fstack-protector-strong
+PURGATORY_CFLAGS_REMOVE		+= -fstack-protector-strong
 endif
 
 ifdef CONFIG_RETPOLINE
-CFLAGS_REMOVE_sha256.o		+= $(RETPOLINE_CFLAGS)
-CFLAGS_REMOVE_purgatory.o	+= $(RETPOLINE_CFLAGS)
-CFLAGS_REMOVE_string.o		+= $(RETPOLINE_CFLAGS)
-CFLAGS_REMOVE_kexec-purgatory.o	+= $(RETPOLINE_CFLAGS)
+PURGATORY_CFLAGS_REMOVE		+= $(RETPOLINE_CFLAGS)
 endif
 
+CFLAGS_REMOVE_purgatory.o	+= $(PURGATORY_CFLAGS_REMOVE)
+CFLAGS_purgatory.o		+= $(PURGATORY_CFLAGS)
+
+CFLAGS_REMOVE_sha256.o		+= $(PURGATORY_CFLAGS_REMOVE)
+CFLAGS_sha256.o			+= $(PURGATORY_CFLAGS)
+
+CFLAGS_REMOVE_string.o		+= $(PURGATORY_CFLAGS_REMOVE)
+CFLAGS_string.o			+= $(PURGATORY_CFLAGS)
+
 $(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE
 		$(call if_changed,ld)
 
-- 
2.12.3