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Subject[PATCH] x86: work around clang IAS bug referencing __force_order
Date
When using the clang integrated assembler, we get a reference
to __force_order that should normally get ignored in a few
rare cases:

ERROR: modpost: "__force_order" [drivers/cpufreq/powernow-k6.ko] undefined!

Add a 'static' definition so any file in which this happens can
have a local copy.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
arch/x86/boot/compressed/pgtable_64.c | 2 ++
arch/x86/include/asm/special_insns.h | 7 +++++++
2 files changed, 9 insertions(+)

diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
index c8862696a47b..8595194cea41 100644
--- a/arch/x86/boot/compressed/pgtable_64.c
+++ b/arch/x86/boot/compressed/pgtable_64.c
@@ -12,7 +12,9 @@
* It is not referenced from the code, but GCC < 5 with -fPIE would fail
* due to an undefined symbol. Define it to make these ancient GCCs work.
*/
+#ifndef CONFIG_CC_IS_CLANG
unsigned long __force_order;
+#endif

#define BIOS_START_MIN 0x20000U /* 128K, less than this is insane */
#define BIOS_START_MAX 0x9f000U /* 640K, absolute maximum */
diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
index 82436cb04ccf..7081e587c1ea 100644
--- a/arch/x86/include/asm/special_insns.h
+++ b/arch/x86/include/asm/special_insns.h
@@ -16,8 +16,15 @@
* A memory clobber would solve the problem, but would prevent reordering of
* all loads stores around it, which can hurt performance. Solution is to
* use a variable and mimic reads and writes to it to enforce serialization
+ *
+ * Clang sometimes fails to kill the reference to the dummy variable, so
+ * provide an actual copy.
*/
+#ifdef CONFIG_CC_IS_CLANG
+static unsigned long __force_order;
+#else
extern unsigned long __force_order;
+#endif

void native_write_cr0(unsigned long val);

--
2.26.2
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