linux-kernel - [PATCH 3/8] x86: Add intrinsics/macros for new rd/wr fs/gs base instructions

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Date:	Mon, 10 Nov 2014 15:55:34 -0800
From:	Andi Kleen <andi@...stfloor.org>
To:	x86@...nel.org
Cc:	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH 3/8] x86: Add intrinsics/macros for new rd/wr fs/gs base instructions

From: Andi Kleen <ak@...ux.intel.com>

Add C intrinsics and assembler macros for the new rd/wr fs/gs base
instructions and for swapgs.

Very straight forward. Used in followon patch.

For assembler only a few standard registers used by entry_64.S
are defined.

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
 arch/x86/include/asm/fsgs.h | 54 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)
 create mode 100644 arch/x86/include/asm/fsgs.h

diff --git a/arch/x86/include/asm/fsgs.h b/arch/x86/include/asm/fsgs.h
new file mode 100644
index 0000000..1df5085
--- /dev/null
+++ b/arch/x86/include/asm/fsgs.h
@@ -0,0 +1,54 @@
+#ifndef _ASM_FSGS_H
+#define _ASM_FSGS_H 1
+
+#ifndef __ASSEMBLY__
+
+static inline void swapgs(void)
+{
+	asm volatile("swapgs" ::: "memory");
+}
+
+/* Must be protected by X86_FEATURE_FSGSBASE check. */
+
+static inline unsigned long rdgsbase(void)
+{
+	unsigned long gs;
+	asm volatile(".byte 0xf3,0x48,0x0f,0xae,0xc8 # rdgsbaseq %%rax"
+			: "=a" (gs)
+			:: "memory");
+	return gs;
+}
+
+static inline unsigned long rdfsbase(void)
+{
+	unsigned long fs;
+	asm volatile(".byte 0xf3,0x48,0x0f,0xae,0xc0 # rdfsbaseq %%rax"
+			: "=a" (fs)
+			:: "memory");
+	return fs;
+}
+
+static inline void wrgsbase(unsigned long gs)
+{
+	asm volatile(".byte 0xf3,0x48,0x0f,0xae,0xd8 # wrgsbaseq %%rax"
+			:: "a" (gs)
+			: "memory");
+}
+
+static inline void wrfsbase(unsigned long fs)
+{
+	asm volatile(".byte 0xf3,0x48,0x0f,0xae,0xd0 # wrfsbaseq %%rax"
+			:: "a" (fs)
+			: "memory");
+}
+
+#else
+
+/* Handle old assemblers. */
+#define RDGSBASE_R15 .byte 0xf3,0x49,0x0f,0xae,0xcf
+#define WRGSBASE_RDI .byte 0xf3,0x48,0x0f,0xae,0xdf
+#define WRGSBASE_R15 .byte 0xf3,0x49,0x0f,0xae,0xdf
+
+#endif /* __ASSEMBLY__ */
+
+#endif
-- 
1.9.3

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