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Subject[PATCH RFC 1/6] Basic definitions for i386-pda
This patch has the basic definitions of struct i386_pda, and the
segment selector in the GDT.

asm-i386/pda.h is more or less a direct copy of asm-x86_64/pda.h. The
most interesting difference is the use of _proxy_pda, which is used to
give gcc a model for the actual memory operations on the real pda
structure. No actual reference is ever made to _proxy_pda, so it is
never defined.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Chuck Ebbert <76306.1226@compuserve.com>
Cc: Zachary Amsden <zach@vmware.com>
Cc: Jan Beulich <jbeulich@novell.com>
Cc: Andi Kleen <ak@suse.de>

---
arch/i386/kernel/asm-offsets.c | 4 ++
arch/i386/kernel/head.S | 2 -
include/asm-i386/pda.h | 67 ++++++++++++++++++++++++++++++++++++++++
include/asm-i386/segment.h | 5 ++
4 files changed, 76 insertions(+), 2 deletions(-)

===================================================================
--- a/arch/i386/kernel/asm-offsets.c
+++ b/arch/i386/kernel/asm-offsets.c
@@ -15,6 +15,7 @@
#include <asm/processor.h>
#include <asm/thread_info.h>
#include <asm/elf.h>
+#include <asm/pda.h>

#define DEFINE(sym, val) \
asm volatile("\n->" #sym " %0 " #val : : "i" (val))
@@ -74,4 +75,7 @@ void foo(void)
DEFINE(VDSO_PRELINK, VDSO_PRELINK);

OFFSET(crypto_tfm_ctx_offset, crypto_tfm, __crt_ctx);
+
+ BLANK();
+ OFFSET(PDA_pcurrent, i386_pda, pcurrent);
}
===================================================================
--- a/arch/i386/kernel/head.S
+++ b/arch/i386/kernel/head.S
@@ -591,7 +591,7 @@ ENTRY(cpu_gdt_table)
.quad 0x004092000000ffff /* 0xc8 APM DS data */

.quad 0x0000920000000000 /* 0xd0 - ESPFIX 16-bit SS */
- .quad 0x0000000000000000 /* 0xd8 - unused */
+ .quad 0x0000000000000000 /* 0xd8 - PDA */
.quad 0x0000000000000000 /* 0xe0 - unused */
.quad 0x0000000000000000 /* 0xe8 - unused */
.quad 0x0000000000000000 /* 0xf0 - unused */
===================================================================
--- a/include/asm-i386/segment.h
+++ b/include/asm-i386/segment.h
@@ -39,7 +39,7 @@
* 25 - APM BIOS support
*
* 26 - ESPFIX small SS
- * 27 - unused
+ * 27 - PDA [ per-cpu private data area ]
* 28 - unused
* 29 - unused
* 30 - unused
@@ -73,6 +73,9 @@

#define GDT_ENTRY_ESPFIX_SS (GDT_ENTRY_KERNEL_BASE + 14)
#define __ESPFIX_SS (GDT_ENTRY_ESPFIX_SS * 8)
+
+#define GDT_ENTRY_PDA (GDT_ENTRY_KERNEL_BASE + 15)
+#define __KERNEL_PDA (GDT_ENTRY_PDA * 8)

#define GDT_ENTRY_DOUBLEFAULT_TSS 31

===================================================================
--- /dev/null
+++ b/include/asm-i386/pda.h
@@ -0,0 +1,67 @@
+#ifndef _I386_PDA_H
+#define _I386_PDA_H
+
+struct i386_pda
+{
+ struct task_struct *pcurrent; /* current process */
+ int cpu_number;
+};
+
+extern struct i386_pda *_cpu_pda[];
+
+#define cpu_pda(i) (_cpu_pda[i])
+
+#define pda_offset(field) offsetof(struct i386_pda, field)
+
+extern void __bad_pda_field(void);
+
+extern struct i386_pda _proxy_pda;
+
+#define pda_to_op(op,field,val) \
+ do { \
+ typedef typeof(_proxy_pda.field) T__; \
+ switch (sizeof(_proxy_pda.field)) { \
+ case 2: \
+ asm(op "w %1,%%gs:%P2" \
+ : "=m" (_proxy_pda.field) \
+ :"ri" ((T__)val), \
+ "i"(pda_offset(field))); \
+ break; \
+ case 4: \
+ asm(op "l %1,%%gs:%P2" \
+ : "=m" (_proxy_pda.field) \
+ :"ri" ((T__)val), \
+ "i"(pda_offset(field))); \
+ break; \
+ default: __bad_pda_field(); \
+ } \
+ } while (0)
+
+#define pda_from_op(op,field) \
+ ({ \
+ typeof(_proxy_pda.field) ret__; \
+ switch (sizeof(_proxy_pda.field)) { \
+ case 2: \
+ asm(op "w %%gs:%P1,%0" \
+ : "=r" (ret__) \
+ : "i" (pda_offset(field)), \
+ "m" (_proxy_pda.field)); \
+ break; \
+ case 4: \
+ asm(op "l %%gs:%P1,%0" \
+ : "=r" (ret__) \
+ : "i" (pda_offset(field)), \
+ "m" (_proxy_pda.field)); \
+ break; \
+ default: __bad_pda_field(); \
+ } \
+ ret__; })
+
+
+#define read_pda(field) pda_from_op("mov",field)
+#define write_pda(field,val) pda_to_op("mov",field,val)
+#define add_pda(field,val) pda_to_op("add",field,val)
+#define sub_pda(field,val) pda_to_op("sub",field,val)
+#define or_pda(field,val) pda_to_op("or",field,val)
+
+#endif /* _I386_PDA_H */
--

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