path: root/arch/parisc/kernel/syscall.S

/* 
 * Linux/PA-RISC Project (http://www.parisc-linux.org/)
 * 
 * System call entry code / Linux gateway page
 * Copyright (c) Matthew Wilcox 1999 <willy@infradead.org>
 * Licensed under the GNU GPL.
 * thanks to Philipp Rumpf, Mike Shaver and various others
 * sorry about the wall, puffin..
 */

/*
How does the Linux gateway page on PA-RISC work?
------------------------------------------------
The Linux gateway page on PA-RISC is "special".
It actually has PAGE_GATEWAY bits set (this is linux terminology; in parisc
terminology it's Execute, promote to PL0) in the page map.  So anything
executing on this page executes with kernel level privilege (there's more to it
than that: to have this happen, you also have to use a branch with a ,gate
completer to activate the privilege promotion).  The upshot is that everything
that runs on the gateway page runs at kernel privilege but with the current
user process address space (although you have access to kernel space via %sr2).
For the 0x100 syscall entry, we redo the space registers to point to the kernel
address space (preserving the user address space in %sr3), move to wide mode if
required, save the user registers and branch into the kernel syscall entry
point.  For all the other functions, we execute at kernel privilege but don't
flip address spaces. The basic upshot of this is that these code snippets are
executed atomically (because the kernel can't be pre-empted) and they may
perform architecturally forbidden (to PL3) operations (like setting control
registers).
*/


#include <asm/asm-offsets.h>
#include <asm/unistd.h>
#include <asm/errno.h>
#include <asm/page.h>
#include <asm/psw.h>
#include <asm/thread_info.h>
#include <asm/assembly.h>
#include <asm/processor.h>
#include <asm/cache.h>

#include <linux/linkage.h>

	/* We fill the empty parts of the gateway page with
 	 * something that will kill the kernel or a
 	 * userspace application.
	 */
#define KILL_INSN	break	0,0

	.level          PA_ASM_LEVEL

	.text

	.import syscall_exit,code
	.import syscall_exit_rfi,code

	/* Linux gateway page is aliased to virtual page 0 in the kernel
	 * address space. Since it is a gateway page it cannot be
	 * dereferenced, so null pointers will still fault. We start
	 * the actual entry point at 0x100. We put break instructions
	 * at the beginning of the page to trap null indirect function
	 * pointers.
	 */

	.align PAGE_SIZE
ENTRY(linux_gateway_page)

        /* ADDRESS 0x00 to 0xb0 = 176 bytes / 4 bytes per insn = 44 insns */
	.rept 44
	KILL_INSN
	.endr

	/* ADDRESS 0xb0 to 0xb8, lws uses two insns for entry */
	/* Light-weight-syscall entry must always be located at 0xb0 */
	/* WARNING: Keep this number updated with table size changes */
#define __NR_lws_entries (3)

lws_entry:
	gate	lws_start, %r0		/* increase privilege */
	depi	3, 31, 2, %r31		/* Ensure we return into user mode. */

	/* Fill from 0xb8 to 0xe0 */
	.rept 10
	KILL_INSN
	.endr

	/* This function MUST be located at 0xe0 for glibc's threading 
	mechanism to work. DO NOT MOVE THIS CODE EVER! */
set_thread_pointer:
	gate	.+8, %r0		/* increase privilege */
	depi	3, 31, 2, %r31		/* Ensure we return into user mode. */
	be	0(%sr7,%r31)		/* return to user space */
	mtctl	%r26, %cr27		/* move arg0 to the control register */

	/* Increase the chance of trapping if random jumps occur to this
	address, fill from 0xf0 to 0x100 */
	.rept 4
	KILL_INSN
	.endr

/* This address must remain fixed at 0x100 for glibc's syscalls to work */
	.align LINUX_GATEWAY_ADDR
linux_gateway_entry:
	gate	.+8, %r0			/* become privileged */
	mtsp	%r0,%sr4			/* get kernel space into sr4 */
	mtsp	%r0,%sr5			/* get kernel space into sr5 */
	mtsp	%r0,%sr6			/* get kernel space into sr6 */

#ifdef CONFIG_64BIT
	/* Store W bit on entry to the syscall in case it's a wide userland
	 * process. */
	ssm	PSW_SM_W, %r1
	extrd,u	%r1,PSW_W_BIT,1,%r1
	/* sp must be aligned on 4, so deposit the W bit setting into
	 * the bottom of sp temporarily */
	or,ev	%r1,%r30,%r30
	b,n	1f
	/* The top halves of argument registers must be cleared on syscall
	 * entry from narrow executable.
	 */
	depdi	0, 31, 32, %r26
	depdi	0, 31, 32, %r25
	depdi	0, 31, 32, %r24
	depdi	0, 31, 32, %r23
	depdi	0, 31, 32, %r22
	depdi	0, 31, 32, %r21
1:	
#endif

	/* We use a rsm/ssm pair to prevent sr3 from being clobbered
	 * by external interrupts.
	 */
	mfsp    %sr7,%r1                        /* save user sr7 */
	rsm	PSW_SM_I, %r0			/* disable interrupts */
	mtsp    %r1,%sr3                        /* and store it in sr3 */

	mfctl   %cr30,%r1
	xor     %r1,%r30,%r30                   /* ye olde xor trick */
	xor     %r1,%r30,%r1
	xor     %r1,%r30,%r30
	
	ldo     THREAD_SZ_ALGN+FRAME_SIZE(%r30),%r30  /* set up kernel stack */

	/* N.B.: It is critical that we don't set sr7 to 0 until r30
	 *       contains a valid kernel stack pointer. It is also
	 *       critical that we don't start using the kernel stack
	 *       until after sr7 has been set to 0.
	 */

	mtsp	%r0,%sr7			/* get kernel space into sr7 */
	ssm	PSW_SM_I, %r0			/* enable interrupts */
	STREGM	%r1,FRAME_SIZE(%r30)		/* save r1 (usp) here for now */
	mfctl	%cr30,%r1			/* get task ptr in %r1 */
	LDREG	TI_TASK(%r1),%r1

	/* Save some registers for sigcontext and potential task
	   switch (see entry.S for the details of which ones are
	   saved/restored).  TASK_PT_PSW is zeroed so we can see whether
	   a process is on a syscall or not.  For an interrupt the real
	   PSW value is stored.  This is needed for gdb and sys_ptrace. */
	STREG	%r0,  TASK_PT_PSW(%r1)
	STREG	%r2,  TASK_PT_GR2(%r1)		/* preserve rp */
	STREG	%r19, TASK_PT_GR19(%r1)

	LDREGM	-FRAME_SIZE(%r30), %r2		/* get users sp back */
#ifdef CONFIG_64BIT
	extrd,u	%r2,63,1,%r19			/* W hidden in bottom bit */
#if 0
	xor	%r19,%r2,%r2			/* clear bottom bit */
	depd,z	%r19,1,1,%r19
	std	%r19,TASK_PT_PSW(%r1)
#endif
#endif
	STREG	%r2,  TASK_PT_GR30(%r1)		/* ... and save it */
	
	STREG	%r20, TASK_PT_GR20(%r1)		/* Syscall number */
	STREG	%r21, TASK_PT_GR21(%r1)
	STREG	%r22, TASK_PT_GR22(%r1)
	STREG	%r23, TASK_PT_GR23(%r1)		/* 4th argument */
	STREG	%r24, TASK_PT_GR24(%r1)		/* 3rd argument */
	STREG	%r25, TASK_PT_GR25(%r1)		/* 2nd argument */
	STREG	%r26, TASK_PT_GR26(%r1)	 	/* 1st argument */
	STREG	%r27, TASK_PT_GR27(%r1)		/* user dp */
	STREG   %r28, TASK_PT_GR28(%r1)         /* return value 0 */
	STREG   %r0, TASK_PT_ORIG_R28(%r1)      /* don't prohibit restarts */
	STREG	%r29, TASK_PT_GR29(%r1)