patch-2.4.20 linux-2.4.20/arch/mips/math-emu/dsemul.c

• Lines: 174
• Date: Thu Nov 28 15:53:10 2002
• Orig file: linux-2.4.19/arch/mips/math-emu/dsemul.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -urN linux-2.4.19/arch/mips/math-emu/dsemul.c linux-2.4.20/arch/mips/math-emu/dsemul.c
@@ -0,0 +1,173 @@
+#include <linux/compiler.h>
+#include <linux/mm.h>
+#include <linux/signal.h>
+#include <linux/smp.h>
+#include <linux/smp_lock.h>
+
+#include <asm/asm.h>
+#include <asm/bootinfo.h>
+#include <asm/byteorder.h>
+#include <asm/cpu.h>
+#include <asm/inst.h>
+#include <asm/processor.h>
+#include <asm/uaccess.h>
+#include <asm/branch.h>
+#include <asm/mipsregs.h>
+#include <asm/system.h>
+#include <asm/pgtable.h>
+
+#include <asm/fpu_emulator.h>
+
+#include "ieee754.h"
+#include "dsemul.h"
+
+/* Strap kernel emulator for full MIPS IV emulation */
+
+#ifdef __mips
+#undef __mips
+#endif
+#define __mips 4
+
+extern struct mips_fpu_emulator_private fpuemuprivate;
+
+
+/*
+ * Emulate the arbritrary instruction ir at xcp->cp0_epc.  Required when
+ * we have to emulate the instruction in a COP1 branch delay slot.  Do
+ * not change cp0_epc due to the instruction
+ *
+ * According to the spec:
+ * 1) it shouldnt be a branch :-)
+ * 2) it can be a COP instruction :-(
+ * 3) if we are tring to run a protected memory space we must take
+ *    special care on memory access instructions :-(
+ */
+
+/*
+ * "Trampoline" return routine to catch exception following
+ *  execution of delay-slot instruction execution.
+ */
+
+struct emuframe {
+	mips_instruction	emul;
+	mips_instruction	badinst;
+	mips_instruction	cookie;
+	gpreg_t			epc;
+};
+
+int mips_dsemul(struct pt_regs *regs, mips_instruction ir, gpreg_t cpc)
+{
+	extern asmlinkage void handle_dsemulret(void);
+	mips_instruction *dsemul_insns;
+	struct emuframe *fr;
+	int err;
+
+	if (ir == 0) {		/* a nop is easy */
+		regs->cp0_epc = cpc;
+		regs->cp0_cause &= ~CAUSEF_BD;
+		return 0;
+	}
+#ifdef DSEMUL_TRACE
+	printk("dsemul %lx %lx\n", regs->cp0_epc, cpc);
+
+#endif
+
+	/*
+	 * The strategy is to push the instruction onto the user stack
+	 * and put a trap after it which we can catch and jump to
+	 * the required address any alternative apart from full
+	 * instruction emulation!!.
+	 *
+	 * Algorithmics used a system call instruction, and
+	 * borrowed that vector.  MIPS/Linux version is a bit
+	 * more heavyweight in the interests of portability and
+	 * multiprocessor support.  For Linux we generate a
+	 * an unaligned access and force an address error exception.
+	 *
+	 * For embedded systems (stand-alone) we prefer to use a
+	 * non-existing CP1 instruction. This prevents us from emulating
+	 * branches, but gives us a cleaner interface to the exception
+	 * handler (single entry point).
+	 */
+
+	/* Ensure that the two instructions are in the same cache line */
+	dsemul_insns = (mips_instruction *) REG_TO_VA ((regs->regs[29] - sizeof(struct emuframe)) & ~0x7);
+	fr = (struct emuframe *) dsemul_insns;
+
+	/* Verify that the stack pointer is not competely insane */
+	if (unlikely(verify_area(VERIFY_WRITE, fr, sizeof(struct emuframe))))
+		return SIGBUS;
+
+	err = __put_user(ir, &fr->emul);
+	err |= __put_user((mips_instruction)BADINST, &fr->badinst);
+	err |= __put_user((mips_instruction)BD_COOKIE, &fr->cookie);
+	err |= __put_user(cpc, &fr->epc);
+
+	if (unlikely(err)) {
+		fpuemuprivate.stats.errors++;
+		return SIGBUS;
+	}
+
+	regs->cp0_epc = VA_TO_REG & fr->emul;
+
+	flush_cache_sigtramp((unsigned long)&fr->badinst);
+
+	return SIGILL;		/* force out of emulation loop */
+}
+
+int do_dsemulret(struct pt_regs *xcp)
+{
+	struct emuframe *fr;
+	gpreg_t epc;
+	u32 insn, cookie;
+	int err = 0;
+
+	fr = (struct emuframe *) (xcp->cp0_epc - sizeof(mips_instruction));
+
+	/*
+	 * If we can't even access the area, something is very wrong, but we'll
+	 * leave that to the default handling
+	 */
+	if (verify_area(VERIFY_READ, fr, sizeof(struct emuframe)))
+		return 0;
+
+	/*
+	 * Do some sanity checking on the stackframe:
+	 *
+	 *  - Is the instruction pointed to by the EPC an BADINST?
+	 *  - Is the following memory word the BD_COOKIE?
+	 */
+	err = __get_user(insn, &fr->badinst);
+	err |= __get_user(cookie, &fr->cookie);
+
+	if (unlikely(err || (insn != BADINST) || (cookie != BD_COOKIE))) {
+		fpuemuprivate.stats.errors++;
+
+		return 0;
+	}
+
+	/*
+	 * At this point, we are satisfied that it's a BD emulation trap.  Yes,
+	 * a user might have deliberately put two malformed and useless
+	 * instructions in a row in his program, in which case he's in for a
+	 * nasty surprise - the next instruction will be treated as a
+	 * continuation address!  Alas, this seems to be the only way that we
+	 * can handle signals, recursion, and longjmps() in the context of
+	 * emulating the branch delay instruction.
+	 */
+
+#ifdef DSEMUL_TRACE
+	printk("dsemulret\n");
+#endif
+	if (__get_user(epc, &fr->epc)) {		/* Saved EPC */
+		/* This is not a good situation to be in */
+		force_sig(SIGBUS, current);
+
+		return 0;
+	}
+
+	/* Set EPC to return to post-branch instruction */
+	xcp->cp0_epc = epc;
+
+	return 1;
+}