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Message-Id: <1dabde8c20c8014327abb8d2e6b1b2fdb1c2d19c.1314207974.git.jeremy.fitzhardinge@citrix.com>
Date: Wed, 24 Aug 2011 10:53:10 -0700
From: Jeremy Fitzhardinge <jeremy@...p.org>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...e.hu>,
the arch/x86 maintainers <x86@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Nick Piggin <npiggin@...nel.dk>,
Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: [PATCH 16/18] x86: report xchg/cmpxchg/xadd usage errors consistently
From: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Make sure that passing a variable of an unusable size causes a consistent
link-time failure. Previously, using a 64-bit value on a 32-bit system
would cause an assember error, which isn't easy to correlate with a line
of code.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
---
arch/x86/include/asm/cmpxchg.h | 44 +++++++++++++++++++++++++++++----------
1 files changed, 32 insertions(+), 12 deletions(-)
diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h
index 57d6706..c99ce79 100644
--- a/arch/x86/include/asm/cmpxchg.h
+++ b/arch/x86/include/asm/cmpxchg.h
@@ -3,8 +3,26 @@
#include <asm/alternative.h> /* Provides LOCK_PREFIX */
+/* Non-existant functions to indicate usage errors at link time. */
extern void __xchg_wrong_size(void);
extern void __cmpxchg_wrong_size(void);
+extern void __xadd_wrong_size(void);
+
+/*
+ * Constants for operation sizes. On 32-bit, the 64-bit size it set to
+ * -1 because sizeof will never return -1, thereby making those switch
+ * case statements guaranteeed dead code which the compiler will
+ * eliminate, and allowing the "missing symbol in the default case" to
+ * indicate a usage error.
+ */
+#define __X86_CASE_B 1
+#define __X86_CASE_W 2
+#define __X86_CASE_L 4
+#ifdef CONFIG_64BIT
+#define __X86_CASE_Q 8
+#else
+#define __X86_CASE_Q -1 /* sizeof will never return -1 */
+#endif
/*
* Note: no "lock" prefix even on SMP: xchg always implies lock anyway.
@@ -16,7 +34,7 @@ extern void __cmpxchg_wrong_size(void);
({ \
__typeof(*(ptr)) __x = (x); \
switch (size) { \
- case 1: \
+ case __X86_CASE_B: \
{ \
volatile u8 *__ptr = (volatile u8 *)(ptr); \
asm volatile("xchgb %0,%1" \
@@ -25,7 +43,7 @@ extern void __cmpxchg_wrong_size(void);
: "memory"); \
break; \
} \
- case 2: \
+ case __X86_CASE_W: \
{ \
volatile u16 *__ptr = (volatile u16 *)(ptr); \
asm volatile("xchgw %0,%1" \
@@ -34,7 +52,7 @@ extern void __cmpxchg_wrong_size(void);
: "memory"); \
break; \
} \
- case 4: \
+ case __X86_CASE_L: \
{ \
volatile u32 *__ptr = (volatile u32 *)(ptr); \
asm volatile("xchgl %0,%1" \
@@ -43,7 +61,7 @@ extern void __cmpxchg_wrong_size(void);
: "memory"); \
break; \
} \
- case 8: \
+ case __X86_CASE_Q: \
{ \
volatile u64 *__ptr = (volatile u64 *)(ptr); \
asm volatile("xchgq %0,%1" \
@@ -72,7 +90,7 @@ extern void __cmpxchg_wrong_size(void);
__typeof__(*(ptr)) __old = (old); \
__typeof__(*(ptr)) __new = (new); \
switch (size) { \
- case 1: \
+ case __X86_CASE_B: \
{ \
volatile u8 *__ptr = (volatile u8 *)(ptr); \
asm volatile(lock "cmpxchgb %2,%1; " compare \
@@ -81,7 +99,7 @@ extern void __cmpxchg_wrong_size(void);
: "memory"); \
break; \
} \
- case 2: \
+ case __X86_CASE_W: \
{ \
volatile u16 *__ptr = (volatile u16 *)(ptr); \
asm volatile(lock "cmpxchgw %2,%1; " compare \
@@ -90,7 +108,7 @@ extern void __cmpxchg_wrong_size(void);
: "memory"); \
break; \
} \
- case 4: \
+ case __X86_CASE_L: \
{ \
volatile u32 *__ptr = (volatile u32 *)(ptr); \
asm volatile(lock "cmpxchgl %2,%1; " compare \
@@ -99,7 +117,7 @@ extern void __cmpxchg_wrong_size(void);
: "memory"); \
break; \
} \
- case 8: \
+ case __X86_CASE_Q: \
{ \
volatile u64 *__ptr = (volatile u64 *)(ptr); \
asm volatile(lock "cmpxchgq %2,%1; " compare \
@@ -178,26 +196,28 @@ extern void __cmpxchg_wrong_size(void);
#define xadd(ptr, inc) \
do { \
switch (sizeof(*(ptr))) { \
- case 1: \
+ case __X86_CASE_B: \
asm volatile (LOCK_PREFIX "xaddb %b0, %1\n" \
: "+r" (inc), "+m" (*(ptr)) \
: : "memory", "cc"); \
break; \
- case 2: \
+ case __X86_CASE_W: \
asm volatile (LOCK_PREFIX "xaddw %w0, %1\n" \
: "+r" (inc), "+m" (*(ptr)) \
: : "memory", "cc"); \
break; \
- case 4: \
+ case __X86_CASE_L: \
asm volatile (LOCK_PREFIX "xaddl %0, %1\n" \
: "+r" (inc), "+m" (*(ptr)) \
: : "memory", "cc"); \
break; \
- case 8: \
+ case __X86_CASE_Q: \
asm volatile (LOCK_PREFIX "xaddq %q0, %1\n" \
: "+r" (inc), "+m" (*(ptr)) \
: : "memory", "cc"); \
break; \
+ default: \
+ __xadd_wrong_size(); \
} \
} while(0)
--
1.7.6
--
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