s390: system call path micro optimization

Add a pointer to the system call table to the thread_info structure.
The TIF_31BIT bit is set or cleared by SET_PERSONALITY exactly once
for the lifetime of a process. With the pointer to the correct system
call table in thread_info the system call code in entry64.S path can
drop the check for TIF_31BIT which saves a couple of instructions.

Signed-off-by: Martin Schwidefsky <[email protected]>

Author: Martin Schwidefsky

arch/s390/include/asm/elf.h

@@ -120,6 +120,7 @@
 
 #include <asm/ptrace.h>
 #include <asm/compat.h>
+#include <asm/syscall.h>
 #include <asm/user.h>
 
 typedef s390_fp_regs elf_fpregset_t;
@@ -181,18 +182,31 @@ extern unsigned long elf_hwcap;
 extern char elf_platform[];
 #define ELF_PLATFORM (elf_platform)
 
-#ifdef CONFIG_64BIT
+#ifndef CONFIG_COMPAT
+#define SET_PERSONALITY(ex) \
+do {								\
+	set_personality(PER_LINUX |				\
+		(current->personality & (~PER_MASK)));		\
+	current_thread_info()->sys_call_table = 		\
+		(unsigned long) &sys_call_table;		\
+} while (0)
+#else /* CONFIG_COMPAT */
 #define SET_PERSONALITY(ex)					\
 do {								\
 	if (personality(current->personality) != PER_LINUX32)	\
 		set_personality(PER_LINUX |			\
 			(current->personality & ~PER_MASK));	\
-	if ((ex).e_ident[EI_CLASS] == ELFCLASS32)		\
+	if ((ex).e_ident[EI_CLASS] == ELFCLASS32) {		\
 		set_thread_flag(TIF_31BIT);			\
-	else							\
+		current_thread_info()->sys_call_table =		\
+			(unsigned long)	&sys_call_table_emu;	\
+	} else {						\
 		clear_thread_flag(TIF_31BIT);			\
+		current_thread_info()->sys_call_table =		\
+			(unsigned long) &sys_call_table;	\
+	}							\
 } while (0)
-#endif /* CONFIG_64BIT */
+#endif /* CONFIG_COMPAT */
 
 #define STACK_RND_MASK	0x7ffUL
 

arch/s390/include/asm/syscall.h

@@ -23,6 +23,7 @@
  * type here is what we want [need] for both 32 bit and 64 bit systems.
  */
 extern const unsigned int sys_call_table[];
+extern const unsigned int sys_call_table_emu[];
 
 static inline long syscall_get_nr(struct task_struct *task,
 				  struct pt_regs *regs)

arch/s390/include/asm/thread_info.h

@@ -41,6 +41,7 @@ struct thread_info {
 	struct task_struct	*task;		/* main task structure */
 	struct exec_domain	*exec_domain;	/* execution domain */
 	unsigned long		flags;		/* low level flags */
+	unsigned long		sys_call_table;	/* System call table address */
 	unsigned int		cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
 	struct restart_block	restart_block;

arch/s390/kernel/asm-offsets.c

@@ -35,6 +35,7 @@ int main(void)
 	DEFINE(__TI_task, offsetof(struct thread_info, task));
 	DEFINE(__TI_domain, offsetof(struct thread_info, exec_domain));
 	DEFINE(__TI_flags, offsetof(struct thread_info, flags));
+	DEFINE(__TI_sysc_table, offsetof(struct thread_info, sys_call_table));
 	DEFINE(__TI_cpu, offsetof(struct thread_info, cpu));
 	DEFINE(__TI_precount, offsetof(struct thread_info, preempt_count));
 	DEFINE(__TI_user_timer, offsetof(struct thread_info, user_timer));

arch/s390/kernel/entry.S

@@ -188,6 +188,7 @@ sysc_vtime:
 	mvc	__PT_INT_CODE(4,%r11),__LC_SVC_ILC
 sysc_do_svc:
 	oi	__TI_flags+3(%r12),_TIF_SYSCALL
+	l	%r10,__TI_sysc_table(%r12)	# 31 bit system call table
 	lh	%r8,__PT_INT_CODE+2(%r11)
 	sla	%r8,2				# shift and test for svc0
 	jnz	sysc_nr_ok
@@ -198,7 +199,6 @@ sysc_do_svc:
 	lr	%r8,%r1
 	sla	%r8,2
 sysc_nr_ok:
-	l	%r10,BASED(.Lsys_call_table)	# 31 bit system call table
 	xc	__SF_BACKCHAIN(4,%r15),__SF_BACKCHAIN(%r15)
 	st	%r2,__PT_ORIG_GPR2(%r11)
 	st	%r7,STACK_FRAME_OVERHEAD(%r15)
@@ -906,7 +906,6 @@ cleanup_idle_wait:
 .Ltrace_enter:		.long	do_syscall_trace_enter
 .Ltrace_exit:		.long	do_syscall_trace_exit
 .Lschedule_tail:	.long	schedule_tail
-.Lsys_call_table:	.long	sys_call_table
 .Lsysc_per:		.long	sysc_per + 0x80000000
 #ifdef CONFIG_TRACE_IRQFLAGS
 .Lhardirqs_on:		.long	trace_hardirqs_on_caller

arch/s390/kernel/entry64.S

@@ -216,6 +216,7 @@ sysc_vtime:
 	mvc	__PT_INT_CODE(4,%r11),__LC_SVC_ILC
 sysc_do_svc:
 	oi	__TI_flags+7(%r12),_TIF_SYSCALL
+	lg	%r10,__TI_sysc_table(%r12)	# address of system call table
 	llgh	%r8,__PT_INT_CODE+2(%r11)
 	slag	%r8,%r8,2			# shift and test for svc 0
 	jnz	sysc_nr_ok
@@ -226,13 +227,6 @@ sysc_do_svc:
 	sth	%r1,__PT_INT_CODE+2(%r11)
 	slag	%r8,%r1,2
 sysc_nr_ok:
-	larl	%r10,sys_call_table		# 64 bit system call table
-#ifdef CONFIG_COMPAT
-	tm	__TI_flags+5(%r12),(_TIF_31BIT>>16)
-	jno	sysc_noemu
-	larl	%r10,sys_call_table_emu		# 31 bit system call table
-sysc_noemu:
-#endif
 	xc	__SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)
 	stg	%r2,__PT_ORIG_GPR2(%r11)
 	stg	%r7,STACK_FRAME_OVERHEAD(%r15)
@@ -1005,6 +999,7 @@ sys_call_table:
 #ifdef CONFIG_COMPAT
 
 #define SYSCALL(esa,esame,emu)	.long emu
+	.globl	sys_call_table_emu
 sys_call_table_emu:
 #include "syscalls.S"
 #undef SYSCALL