xen/arm: Start to implement an ARM decoder instruction

Some errata on ARM processor requires to decode the instruction.
The decoder will, obviously, decode and fill the ISS fields of the hsr_dabt.

For the moment, the decoder only supports:
    - THUMB2 store instruction
    - THUMB single load/store instruction

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

xen/arch/arm/Makefile

@@ -30,6 +30,7 @@ obj-y += vtimer.o
 obj-y += vuart.o
 obj-y += hvm.o
 obj-y += device.o
+obj-y += decode.o
 
 #obj-bin-y += ....o
 

xen/arch/arm/decode.c

@@ -0,0 +1,165 @@
+/*
+ * xen/arch/arm/decode.c
+ *
+ * Instruction decoder
+ *
+ * Julien Grall <julien.grall@linaro.org>
+ * Copyright (C) 2013 Linaro Limited.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <xen/types.h>
+#include <xen/sched.h>
+#include <asm/current.h>
+#include <asm/guest_access.h>
+#include <xen/lib.h>
+
+#include "decode.h"
+
+static void update_dabt(struct hsr_dabt *dabt, int reg,
+                        uint8_t size, bool_t sign)
+{
+    dabt->reg = reg;
+    dabt->size = size;
+    dabt->sign = sign;
+}
+
+static int decode_thumb2(register_t pc, struct hsr_dabt *dabt, uint16_t hw1)
+{
+    uint16_t hw2;
+    int rc;
+    uint16_t rt;
+
+    rc = raw_copy_from_guest(&hw2, (void *__user)(pc + 2), sizeof (hw2));
+    if ( rc )
+        return rc;
+
+    rt = (hw2 >> 12) & 0x7;
+
+    switch ( (hw1 >> 9) & 0xf )
+    {
+    case 12:
+    {
+        bool_t sign = !!(hw1 & (1 << 8));
+        bool_t load = !!(hw1 & (1 << 4));
+
+        if ( (hw1 & 0x0110) == 0x0100 )
+            /* NEON instruction */
+            goto bad_thumb2;
+
+        if ( (hw1 & 0x0070) == 0x0070 )
+            /* Undefined opcodes */
+            goto bad_thumb2;
+
+        /* Store/Load single data item */
+        if ( rt == 15 )
+            /* XXX: Rt == 15 is only invalid for store instruction */
+            goto bad_thumb2;
+
+        if ( !load && sign )
+            /* Store instruction doesn't support sign extension */
+            goto bad_thumb2;
+
+        update_dabt(dabt, rt, (hw1 >> 5) & 3, sign);
+
+        break;
+    }
+    default:
+        goto bad_thumb2;
+    }
+
+    return 0;
+
+bad_thumb2:
+    gdprintk(XENLOG_ERR, "unhandled THUMB2 instruction 0x%x%x\n", hw1, hw2);
+
+    return 1;
+}
+
+static int decode_thumb(register_t pc, struct hsr_dabt *dabt)
+{
+    uint16_t instr;
+    int rc;
+
+    rc = raw_copy_from_guest(&instr, (void * __user)pc, sizeof (instr));
+    if ( rc )
+        return rc;
+
+    switch ( instr >> 12 )
+    {
+    case 5:
+    {
+        /* Load/Store register */
+        uint16_t opB = (instr >> 9) & 0x7;
+        int reg = instr & 7;
+
+        switch ( opB & 0x3 )
+        {
+        case 0: /* Non-signed word */
+            update_dabt(dabt, reg, 2, 0);
+            break;
+        case 1: /* Non-signed halfword */
+            update_dabt(dabt, reg, 1, 0);
+            break;
+        case 2: /* Non-signed byte */
+            update_dabt(dabt, reg, 0, 0);
+            break;
+        case 3: /* Signed byte */
+            update_dabt(dabt, reg, 0, 1);
+            break;
+        }
+
+        break;
+    }
+    case 6:
+        /* Load/Store word immediate offset */
+        update_dabt(dabt, instr & 7, 2, 0);
+        break;
+    case 7:
+        /* Load/Store byte immediate offset */
+        update_dabt(dabt, instr & 7, 0, 0);
+        break;
+    case 8:
+        /* Load/Store halfword immediate offset */
+        update_dabt(dabt, instr & 7, 1, 0);
+        break;
+    case 9:
+        /* Load/Store word sp offset */
+        update_dabt(dabt, (instr >> 8) & 7, 2, 0);
+        break;
+    case 14:
+        if ( instr & (1 << 11) )
+            return decode_thumb2(pc, dabt, instr);
+        goto bad_thumb;
+    case 15:
+        return decode_thumb2(pc, dabt, instr);
+    default:
+        goto bad_thumb;
+    }
+
+    return 0;
+
+bad_thumb:
+    gdprintk(XENLOG_ERR, "unhandled THUMB instruction 0x%x\n", instr);
+    return 1;
+}
+
+int decode_instruction(const struct cpu_user_regs *regs, struct hsr_dabt *dabt)
+{
+    if ( is_pv32_domain(current->domain) && regs->cpsr & PSR_THUMB )
+        return decode_thumb(regs->pc, dabt);
+
+    /* TODO: Handle ARM instruction */
+    gdprintk(XENLOG_ERR, "unhandled ARM instruction\n");
+
+    return 1;
+}

xen/arch/arm/decode.h

@@ -0,0 +1,49 @@
+/*
+ * xen/arch/arm/decode.h
+ *
+ * Instruction decoder
+ *
+ * Julien Grall <julien.grall@linaro.org>
+ * Copyright (C) 2013 Linaro Limited.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#ifndef __ARCH_ARM_DECODE_H_
+#define __ARCH_ARM_DECODE_H_
+
+#include <asm/regs.h>
+#include <asm/processor.h>
+
+/**
+ * Decode an instruction from pc
+ * /!\ This function is not intended to fully decode an instruction. It
+ * considers that the instruction is valid.
+ *
+ * This function will get:
+ *  - The transfer register
+ *  - Sign bit
+ *  - Size
+ */
+
+int decode_instruction(const struct cpu_user_regs *regs,
+                       struct hsr_dabt *dabt);
+
+#endif /* __ARCH_ARM_DECODE_H_ */
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */