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Subjectsysenter support
I've added sysenter/sysexit support for all syscalls with up to 4
parameters.
The syscalls with 5 or 6 parameters must continue to use int $0x80, I
need 2 registers to pass the user space stack and instruction pointer
values. The sysenter instruction destroys them.

sysenter is supported by AMD K7 and Intel Pentium II and later.
Result: simple syscall (getpid()) more than 35% faster.

before: 295 cpu ticks
now: 186 cpu ticks.

patch attached, sample code on
http://colorfullife.com/~manfred/sysenter

syscall support for K6/2 is not planned :-(

--
Manfred// $Header$
// Kernel Version:
// VERSION = 2
// PATCHLEVEL = 4
// SUBLEVEL = 14
// EXTRAVERSION =-pre3
diff -urN 2.4/include/asm-i386/msr.h build-2.4/include/asm-i386/msr.h
--- 2.4/include/asm-i386/msr.h Sun Sep 30 16:25:49 2001
+++ build-2.4/include/asm-i386/msr.h Sat Oct 27 22:30:06 2001
@@ -53,6 +53,10 @@

#define MSR_IA32_BBL_CR_CTL 0x119

+#define MSR_IA32_SYSENTER_CS 0x174
+#define MSR_IA32_SYSENTER_ESP 0x175
+#define MSR_IA32_SYSENTER_EIP 0x176
+
#define MSR_IA32_MCG_CAP 0x179
#define MSR_IA32_MCG_STATUS 0x17a
#define MSR_IA32_MCG_CTL 0x17b
diff -urN 2.4/include/asm-i386/processor.h build-2.4/include/asm-i386/processor.h
--- 2.4/include/asm-i386/processor.h Sun Oct 28 02:12:45 2001
+++ build-2.4/include/asm-i386/processor.h Sat Oct 27 22:27:46 2001
@@ -90,6 +90,7 @@
#define cpu_has_xmm (test_bit(X86_FEATURE_XMM, boot_cpu_data.x86_capability))
#define cpu_has_fpu (test_bit(X86_FEATURE_FPU, boot_cpu_data.x86_capability))
#define cpu_has_apic (test_bit(X86_FEATURE_APIC, boot_cpu_data.x86_capability))
+#define cpu_has_sep (test_bit(X86_FEATURE_SEP, boot_cpu_data.x86_capability))

extern char ignore_irq13;

diff -urN 2.4/include/asm-i386/syscall.h build-2.4/include/asm-i386/syscall.h
--- 2.4/include/asm-i386/syscall.h Thu Jan 1 01:00:00 1970
+++ build-2.4/include/asm-i386/syscall.h Sun Oct 28 10:14:35 2001
@@ -0,0 +1,128 @@
+#ifndef __ASM_SYSCALL_H
+#define __ASM_SYSCALL_H
+#ifdef __KERNEL__
+/*
+ * Helper structures for fast system call instructions.
+ *
+ * Intel support sysenter/sysexit since Pentium II.
+ * AMD supports sysenter/sysexit since K7.
+ * AMD supports syscall and sysret since K6 (/2?)
+ *
+ * Copyright (C) 2001 Manfred Spraul
+ *
+ * A) SYSENTER/SYSEXIT
+ * Interrupts are disabled after sysenter until the normal
+ * stack layout is built.
+ *
+ * sysenter only switches EIP and ESP, and then
+ * entry.S must find current.
+ */
+union sysenter_struct {
+ struct {
+ /* small emergency stack to handle trap flag
+ * debug exceptions. Only 4 dwords are needed.
+ */
+ unsigned long TF_stack[8];
+ /* esp points to cur_tsk after sysenter */
+ void * cur_tsk;
+ } u;
+ unsigned char fill[SMP_CACHE_BYTES];
+};
+extern union sysenter_struct sysenter_data[NR_CPUS];
+/*
+ * B) SYSCALL/SYSRET
+ *
+ * Not yet implemented. I can't find a clean way to
+ * implement SMP support and trap flag clearing.
+ */
+#endif
+
+/* Alternate syscall macros for sysenter and syscall */
+/* A) sysenter
+ * - only up to 4 parametesr
+ */
+
+/* XXX - _foo needs to be __foo, while __NR_bar could be _NR_bar. */
+#define _syscallSEP0(type,name) \
+type name(void) \
+{ \
+long __res; \
+__asm__ __volatile__( \
+ "mov $1f, %%edi\n\t" \
+ "push %%ebp\n\t" \
+ "mov %%esp, %%ebp\n\t" \
+ "sysenter\n\t" \
+ "1:pop %%ebp\n\t" \
+ : "=a" (__res) \
+ : "0" (__NR_##name) \
+ : "ecx", "edx", "edi", "flags"); \
+__syscall_return(type,__res); \
+}
+
+#define _syscallSEP1(type,name,type1,arg1) \
+type name(type1 arg1) \
+{ \
+long __res; \
+__asm__ __volatile__( \
+ "mov $1f, %%edi\n\t" \
+ "push %%ebp\n\t" \
+ "mov %%esp, %%ebp\n\t" \
+ "sysenter\n\t" \
+ "1:pop %%ebp\n\t" \
+ : "=a" (__res) \
+ : "0" (__NR_##name), "b" ((long)(arg1)) \
+ : "ecx", "edx", "edi", "flags"); \
+__syscall_return(type,__res); \
+}
+
+#define _syscallSEP2(type,name,type1,arg1,type2,arg2) \
+type name(type1 arg1,type2 arg2) \
+{ \
+long __res; \
+__asm__ __volatile__( \
+ "mov $1f, %%edi\n\t" \
+ "push %%ebp\n\t" \
+ "mov %%esp, %%ebp\n\t" \
+ "sysenter\n\t" \
+ "1:pop %%ebp\n\t" \
+ : "=a" (__res) \
+ : "0" (__NR_##name), "b" ((long)(arg1)), "c" ((long)(arg2)) \
+ : "edx", "edi", "flags"); \
+__syscall_return(type,__res); \
+}
+
+#define _syscallSEP3(type,name,type1,arg1,type2,arg2,type3,arg3) \
+type name(type1 arg1,type2 arg2,type3 arg3) \
+{ \
+long __res; \
+__asm__ __volatile__( \
+ "mov $1f, %%edi\n\t" \
+ "push %%ebp\n\t" \
+ "mov %%esp, %%ebp\n\t" \
+ "sysenter\n\t" \
+ "1:pop %%ebp\n\t" \
+ : "=a" (__res) \
+ : "0" (__NR_##name), "b" ((long)(arg1)), "c" ((long)(arg2)) \
+ "d" ((long)(arg3)) \
+ : "edi", "flags"); \
+__syscall_return(type,__res); \
+}
+
+#define _syscallSEP4(type,name,type1,arg1,type2,arg2,type3,arg3,type4,arg4) \
+type name (type1 arg1, type2 arg2, type3 arg3, type4 arg4) \
+{ \
+long __res; \
+__asm__ __volatile__( \
+ "mov $1f, %%edi\n\t" \
+ "push %%ebp\n\t" \
+ "mov %%esp, %%ebp\n\t" \
+ "sysenter\n\t" \
+ "1:pop %%ebp\n\t" \
+ : "=a" (__res) \
+ : "0" (__NR_##name), "b" ((long)(arg1)), "c" ((long)(arg2)) \
+ "d" ((long)(arg3)),"S" ((long)(arg4)) \
+ : "edi", "flags"); \
+__syscall_return(type,__res); \
+}
+
+#endif
--- 2.4/arch/i386/kernel/setup.c Sun Oct 28 10:07:01 2001
+++ build-2.4/arch/i386/kernel/setup.c Sun Oct 28 00:42:50 2001
@@ -108,6 +108,7 @@
#include <asm/dma.h>
#include <asm/mpspec.h>
#include <asm/mmu_context.h>
+#include <asm/syscall.h>
/*
* Machine setup..
*/
@@ -2771,6 +2772,7 @@
* and IDT. We reload them nevertheless, this function acts as a
* 'CPU state barrier', nothing should get across.
*/
+extern void system_call_SYSENTER(void);
void __init cpu_init (void)
{
int nr = smp_processor_id();
@@ -2832,6 +2834,12 @@
current->flags &= ~PF_USEDFPU;
current->used_math = 0;
stts();
+
+ if (cpu_has_sep) {
+ wrmsr(MSR_IA32_SYSENTER_CS, 0x10, 0);
+ wrmsr(MSR_IA32_SYSENTER_ESP, &sysenter_data[nr].u.cur_tsk, 0);
+ wrmsr(MSR_IA32_SYSENTER_EIP, system_call_SYSENTER, 0);
+ }
}

/*
--- 2.4/arch/i386/kernel/process.c Thu Oct 11 15:19:41 2001
+++ build-2.4/arch/i386/kernel/process.c Sun Oct 28 00:16:22 2001
@@ -43,6 +43,7 @@
#include <asm/i387.h>
#include <asm/desc.h>
#include <asm/mmu_context.h>
+#include <asm/syscall.h>
#ifdef CONFIG_MATH_EMULATION
#include <asm/math_emu.h>
#endif
@@ -650,6 +651,8 @@
: /* no output */ \
:"r" (thread->debugreg[register]))

+union sysenter_struct sysenter_data[NR_CPUS];
+
/*
* switch_to(x,yn) should switch tasks from x to y.
*
@@ -679,6 +682,7 @@
*next = &next_p->thread;
struct tss_struct *tss = init_tss + smp_processor_id();

+ sysenter_data[smp_processor_id()].u.cur_tsk = current;
unlazy_fpu(prev_p);

/*
--- 2.4/arch/i386/kernel/traps.c Sun Oct 28 02:12:43 2001
+++ build-2.4/arch/i386/kernel/traps.c Sat Oct 27 22:57:07 2001
@@ -921,7 +921,7 @@
#endif

set_trap_gate(0,&divide_error);
- set_trap_gate(1,&debug);
+ set_intr_gate(1,&debug);
set_intr_gate(2,&nmi);
set_system_gate(3,&int3); /* int3-5 can be called from all */
set_system_gate(4,&overflow);
--- 2.4/arch/i386/kernel/entry.S Sun Oct 28 02:12:43 2001
+++ build-2.4/arch/i386/kernel/entry.S Sun Oct 28 09:48:25 2001
@@ -45,6 +45,7 @@
#include <linux/linkage.h>
#include <asm/segment.h>
#include <asm/smp.h>
+#include <asm/unistd.h>

EBX = 0x00
ECX = 0x04
@@ -97,7 +98,7 @@
movl %edx,%ds; \
movl %edx,%es;

-#define RESTORE_ALL \
+#define RESTORE_NORET \
popl %ebx; \
popl %ecx; \
popl %edx; \
@@ -107,14 +108,22 @@
popl %eax; \
1: popl %ds; \
2: popl %es; \
- addl $4,%esp; \
-3: iret; \
.section .fixup,"ax"; \
-4: movl $0,(%esp); \
+3: movl $0,(%esp); \
jmp 1b; \
-5: movl $0,(%esp); \
+4: movl $0,(%esp); \
jmp 2b; \
-6: pushl %ss; \
+.previous; \
+.section __ex_table,"a";\
+ .align 4; \
+ .long 1b,3b; \
+ .long 2b,4b; \
+.previous
+
+#define DO_IRET \
+1: iret; \
+.section .fixup,"ax"; \
+2: pushl %ss; \
popl %ds; \
pushl %ss; \
popl %es; \
@@ -122,12 +131,15 @@
call do_exit; \
.previous; \
.section __ex_table,"a";\
- .align 4; \
- .long 1b,4b; \
- .long 2b,5b; \
- .long 3b,6b; \
+ .long 1b,2b; \
.previous

+
+#define RESTORE_ALL \
+ RESTORE_NORET \
+ addl $4,%esp; \
+ DO_IRET
+
#define GET_CURRENT(reg) \
movl $-8192, reg; \
andl %esp, reg
@@ -259,6 +271,92 @@
call SYMBOL_NAME(schedule) # test
jmp ret_from_sys_call

+/*
+ * SYSENTER entry point
+ * ptrace must work without changes, thus the code pushes everything
+ * identical to int 0x80
+ */
+
+ENTRY(system_call_SYSENTER)
+ movl (%esp), %esp # load current
+ addl $0x2000, %esp # and go to the stack
+ sti
+ pushl $0x2b # user ss
+ pushl %ebp # user esp
+ pushfl
+ pushl $0x23 # user cs
+ pushl %edi # user eip
+
+ pushl %eax # orig_eax
+
+ SAVE_ALL
+ GET_CURRENT(%ebx)
+ cmpl $(NR_syscalls),%eax
+ jae badsys
+ testb $0x02,tsk_ptrace(%ebx) # PT_TRACESYS
+ jne tracesys
+ call *SYMBOL_NAME(sys_call_table)(,%eax,4)
+ movl %eax,EAX(%esp) # save the return value
+ cli # need_resched and signals atomic test
+ cmpl $0,need_resched(%ebx)
+ jne reschedule
+ cmpl $0,sigpending(%ebx)
+ jne signal_return
+ #
+ # for return from execve and sigreturn, we must use iretd,
+ # since we must not clobber %ecx and %edx in these cases.
+ #
+ # FIXME: ak says that iopl is special, too.
+ RESTORE_NORET
+ cmpl $__NR_execve, (%esp)
+ je sysexit_iretd
+ cmpl $__NR_sigreturn, (%esp)
+ je sysexit_iretd
+ popl %edx # discard orig_eax
+ popl %edx # user eip
+ popl %ecx # discard user cs
+
+ movl 4(%esp),%ecx # user esp
+ # popfl reenables interrupts.
+ # To guarantee an atomic enable & return,
+ # that must be the last instruction before sysexit
+ # FIXME: check docu. hpa says ok.
+ popfl
+ # Alternative:
+ # andl $0xfffffdff, (%esp)
+ # popfl
+ # sti
+ sysexit
+ # user esp was already loaded
+ # ignore user ss
+sysexit_iretd:
+ DO_IRET
+
+
+sysenter_trap_fixup:
+ # Sysenter was called single stepping is on.
+ # We must transparently switch from sysenter to int $0x80.
+ # Sysexit does not support enabling the trap flag.
+ # Stack layout:
+ pushl %eax
+ movl %esp, %eax
+ # 0(%eax): true eax
+ # 4(%eax): EIP (==system_call_SYSENTER)
+ # 8(%eax): CS (==KERNEL_CS)
+ # 12(%eax): flags
+ # 16(%eax): current
+ movl 16(%esp), %esp
+ addl $0x2000, %esp
+ sti
+ pushl $0x2b # user ss
+ pushl %ebp # user esp
+ orl $0x200, 12(%eax) # enable interrupts, sysenter disabled them
+ pushl 12(%eax) # flags
+ pushl $0x23 # user cs
+ pushl %edi # user eip
+ movl (%eax), %eax
+ jmp system_call
+
ENTRY(divide_error)
pushl $0 # no error code
pushl $ SYMBOL_NAME(do_divide_error)
@@ -317,6 +415,9 @@
jmp ret_from_exception

ENTRY(debug)
+ cmpl $system_call_SYSENTER, (%esp)
+ je sysenter_trap_fixup
+ sti
pushl $0
pushl $ SYMBOL_NAME(do_debug)
jmp error_code
\
 
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