Re: [4.4.y] llvmlinux: Backport "x86/hweight: Get rid of the special calling convention"

[Sedat Dilek]

> The patch I had in series is now obsolete.
>

That's the correct one.

- Sedat -
From 5a10fe05cb0b8169b7616f79471e50751f3222f5 Mon Sep 17 00:00:00 2001
From: Sedat Dilek <sedat.dilek@xxxxxxxxx>
Date: Mon, 12 Oct 2015 09:39:28 +0200
Subject: [PATCH] x86/hweight: boot: llvmlinux: Workaround LLVM Bug PR9457

This workaround is required to boot my Ubuntu/precise AMD64 system when
building with '-no-integrated-as' compiler-flag.

For more details see [1].
See also [2], when IA is used.

Tested with Clang v3.7 and v3.8 against Linux v4.3.y and v4.4.y kernels.

[1] https://llvm.org/bugs/show_bug.cgi?id=9457
[2] https://llvm.org/bugs/show_bug.cgi?id=24487
---
 arch/x86/Kconfig                    |  4 ++--
 arch/x86/include/asm/arch_hweight.h | 18 ++++--------------
 2 files changed, 6 insertions(+), 16 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index db3622f22b61..9c79418cb783 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -280,8 +280,8 @@ config X86_32_LAZY_GS
 
 config ARCH_HWEIGHT_CFLAGS
 	string
-	default "-fcall-saved-ecx -fcall-saved-edx" if X86_32
-	default "-fcall-saved-rdi -fcall-saved-rsi -fcall-saved-rdx -fcall-saved-rcx -fcall-saved-r8 -fcall-saved-r9 -fcall-saved-r10 -fcall-saved-r11" if X86_64
+	# Workaround LLVM Bug PR9457
+	default "" if (X86_32 || X86_64)
 
 config ARCH_SUPPORTS_UPROBES
 	def_bool y
diff --git a/arch/x86/include/asm/arch_hweight.h b/arch/x86/include/asm/arch_hweight.h
index 259a7c1ef709..33f828a659bc 100644
--- a/arch/x86/include/asm/arch_hweight.h
+++ b/arch/x86/include/asm/arch_hweight.h
@@ -23,13 +23,8 @@
  */
 static __always_inline unsigned int __arch_hweight32(unsigned int w)
 {
-	unsigned int res = 0;
-
-	asm (ALTERNATIVE("call __sw_hweight32", POPCNT32, X86_FEATURE_POPCNT)
-		     : "="REG_OUT (res)
-		     : REG_IN (w));
-
-	return res;
+/* Workaround LLVM Bug PR9457 */
+	return __sw_hweight32(w);
 }
 
 static inline unsigned int __arch_hweight16(unsigned int w)
@@ -51,13 +46,8 @@ static inline unsigned long __arch_hweight64(__u64 w)
 #else
 static __always_inline unsigned long __arch_hweight64(__u64 w)
 {
-	unsigned long res = 0;
-
-	asm (ALTERNATIVE("call __sw_hweight64", POPCNT64, X86_FEATURE_POPCNT)
-		     : "="REG_OUT (res)
-		     : REG_IN (w));
-
-	return res;
+/* Workaround LLVM Bug PR9457 */
+	return __sw_hweight64(w);
 }
 #endif /* CONFIG_X86_32 */
 
-- 
2.9.0