target-arm: Implement setting of watchpoints

Implement support for setting QEMU watchpoints based on the
values the guest writes to the ARM architected watchpoint
registers. (We do not yet report the firing of the watchpoints
to the guest, so they will just be ignored.)
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

target-arm/cpu.c

@@ -184,6 +184,8 @@ static void arm_cpu_reset(CPUState *s)
         kvm_arm_reset_vcpu(cpu);
     }
 #endif
+
+    hw_watchpoint_update_all(cpu);
 }
 
 #ifndef CONFIG_USER_ONLY

target-arm/cpu.h

@@ -323,6 +323,8 @@ typedef struct CPUARMState {
     int eabi;
 #endif
 
+    struct CPUWatchpoint *cpu_watchpoint[16];
+
     CPU_COMMON
 
     /* These fields after the common ones so they are preserved on reset.  */

target-arm/helper.c

@@ -2279,6 +2279,131 @@ static const ARMCPRegInfo debug_lpae_cp_reginfo[] = {
     REGINFO_SENTINEL
 };
 
+void hw_watchpoint_update(ARMCPU *cpu, int n)
+{
+    CPUARMState *env = &cpu->env;
+    vaddr len = 0;
+    vaddr wvr = env->cp15.dbgwvr[n];
+    uint64_t wcr = env->cp15.dbgwcr[n];
+    int mask;
+    int flags = BP_CPU | BP_STOP_BEFORE_ACCESS;
+
+    if (env->cpu_watchpoint[n]) {
+        cpu_watchpoint_remove_by_ref(CPU(cpu), env->cpu_watchpoint[n]);
+        env->cpu_watchpoint[n] = NULL;
+    }
+
+    if (!extract64(wcr, 0, 1)) {
+        /* E bit clear : watchpoint disabled */
+        return;
+    }
+
+    switch (extract64(wcr, 3, 2)) {
+    case 0:
+        /* LSC 00 is reserved and must behave as if the wp is disabled */
+        return;
+    case 1:
+        flags |= BP_MEM_READ;
+        break;
+    case 2:
+        flags |= BP_MEM_WRITE;
+        break;
+    case 3:
+        flags |= BP_MEM_ACCESS;
+        break;
+    }
+
+    /* Attempts to use both MASK and BAS fields simultaneously are
+     * CONSTRAINED UNPREDICTABLE; we opt to ignore BAS in this case,
+     * thus generating a watchpoint for every byte in the masked region.
+     */
+    mask = extract64(wcr, 24, 4);
+    if (mask == 1 || mask == 2) {
+        /* Reserved values of MASK; we must act as if the mask value was
+         * some non-reserved value, or as if the watchpoint were disabled.
+         * We choose the latter.
+         */
+        return;
+    } else if (mask) {
+        /* Watchpoint covers an aligned area up to 2GB in size */
+        len = 1ULL << mask;
+        /* If masked bits in WVR are not zero it's CONSTRAINED UNPREDICTABLE
+         * whether the watchpoint fires when the unmasked bits match; we opt
+         * to generate the exceptions.
+         */
+        wvr &= ~(len - 1);
+    } else {
+        /* Watchpoint covers bytes defined by the byte address select bits */
+        int bas = extract64(wcr, 5, 8);
+        int basstart;
+
+        if (bas == 0) {
+            /* This must act as if the watchpoint is disabled */
+            return;
+        }
+
+        if (extract64(wvr, 2, 1)) {
+            /* Deprecated case of an only 4-aligned address. BAS[7:4] are
+             * ignored, and BAS[3:0] define which bytes to watch.
+             */
+            bas &= 0xf;
+        }
+        /* The BAS bits are supposed to be programmed to indicate a contiguous
+         * range of bytes. Otherwise it is CONSTRAINED UNPREDICTABLE whether
+         * we fire for each byte in the word/doubleword addressed by the WVR.
+         * We choose to ignore any non-zero bits after the first range of 1s.
+         */
+        basstart = ctz32(bas);
+        len = cto32(bas >> basstart);
+        wvr += basstart;
+    }
+
+    cpu_watchpoint_insert(CPU(cpu), wvr, len, flags,
+                          &env->cpu_watchpoint[n]);
+}
+
+void hw_watchpoint_update_all(ARMCPU *cpu)
+{
+    int i;
+    CPUARMState *env = &cpu->env;
+
+    /* Completely clear out existing QEMU watchpoints and our array, to
+     * avoid possible stale entries following migration load.
+     */
+    cpu_watchpoint_remove_all(CPU(cpu), BP_CPU);
+    memset(env->cpu_watchpoint, 0, sizeof(env->cpu_watchpoint));
+
+    for (i = 0; i < ARRAY_SIZE(cpu->env.cpu_watchpoint); i++) {
+        hw_watchpoint_update(cpu, i);
+    }
+}
+
+static void dbgwvr_write(CPUARMState *env, const ARMCPRegInfo *ri,
+                         uint64_t value)
+{
+    ARMCPU *cpu = arm_env_get_cpu(env);
+    int i = ri->crm;
+
+    /* Bits [63:49] are hardwired to the value of bit [48]; that is, the
+     * register reads and behaves as if values written are sign extended.
+     * Bits [1:0] are RES0.
+     */
+    value = sextract64(value, 0, 49) & ~3ULL;
+
+    raw_write(env, ri, value);
+    hw_watchpoint_update(cpu, i);
+}
+
+static void dbgwcr_write(CPUARMState *env, const ARMCPRegInfo *ri,
+                         uint64_t value)
+{
+    ARMCPU *cpu = arm_env_get_cpu(env);
+    int i = ri->crm;
+
+    raw_write(env, ri, value);
+    hw_watchpoint_update(cpu, i);
+}
+
 static void define_debug_regs(ARMCPU *cpu)
 {
     /* Define v7 and v8 architectural debug registers.
@@ -2330,12 +2455,16 @@ static void define_debug_regs(ARMCPU *cpu)
             { .name = "DBGWVR", .state = ARM_CP_STATE_BOTH,
               .cp = 14, .opc0 = 2, .opc1 = 0, .crn = 0, .crm = i, .opc2 = 6,
               .access = PL1_RW,
-              .fieldoffset = offsetof(CPUARMState, cp15.dbgwvr[i]) },
+              .fieldoffset = offsetof(CPUARMState, cp15.dbgwvr[i]),
+              .writefn = dbgwvr_write, .raw_writefn = raw_write
+            },
             { .name = "DBGWCR", .state = ARM_CP_STATE_BOTH,
               .cp = 14, .opc0 = 2, .opc1 = 0, .crn = 0, .crm = i, .opc2 = 7,
               .access = PL1_RW,
-              .fieldoffset = offsetof(CPUARMState, cp15.dbgwcr[i]) },
-               REGINFO_SENTINEL
+              .fieldoffset = offsetof(CPUARMState, cp15.dbgwcr[i]),
+              .writefn = dbgwcr_write, .raw_writefn = raw_write
+            },
+            REGINFO_SENTINEL
         };
         define_arm_cp_regs(cpu, dbgregs);
     }

target-arm/internals.h

@@ -296,4 +296,14 @@ static inline uint32_t syn_swstep(int same_el, int isv, int ex)
         | (isv << 24) | (ex << 6) | 0x22;
 }
 
+/* Update a QEMU watchpoint based on the information the guest has set in the
+ * DBGWCR<n>_EL1 and DBGWVR<n>_EL1 registers.
+ */
+void hw_watchpoint_update(ARMCPU *cpu, int n);
+/* Update the QEMU watchpoints for every guest watchpoint. This does a
+ * complete delete-and-reinstate of the QEMU watchpoint list and so is
+ * suitable for use after migration or on reset.
+ */
+void hw_watchpoint_update_all(ARMCPU *cpu);
+
 #endif

target-arm/machine.c

@@ -2,6 +2,7 @@
 #include "hw/boards.h"
 #include "sysemu/kvm.h"
 #include "kvm_arm.h"
+#include "internals.h"
 
 static bool vfp_needed(void *opaque)
 {
@@ -213,6 +214,8 @@ static int cpu_post_load(void *opaque, int version_id)
         }
     }
 
+    hw_watchpoint_update_all(cpu);
+
     return 0;
 }