target-arm: kvm - re-inject guest debug exceptions

If we can't find details for the debug exception in our debug state
then we can assume the exception is due to debugging inside the guest.
To inject the exception into the guest state we re-use the TCG exception
code (do_interrupt).

However while guest debugging is in effect we currently can't handle the
guest using single step as we will keep trapping to back to userspace.
GDB makes heavy use of single-step behind the scenes which effectively
means the guest's ability to debug itself is disabled while it is being
debugged.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 1449599553-24713-6-git-send-email-alex.bennee@linaro.org
[PMM: Fixed a few typos in comments and commit message]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

diff --git a/target-arm/helper-a64.c b/target-arm/helper-a64.c
index deb8dbe489f0a3a2e092f325d787474bb423eede..fc3ccdf2a774a977785d33e8fc70a5b28bb06c71 100644 (file)
--- a/target-arm/helper-a64.c
+++ b/target-arm/helper-a64.c
@@ -25,6 +25,7 @@
 #include "qemu/bitops.h"
 #include "internals.h"
 #include "qemu/crc32c.h"
+#include "sysemu/kvm.h"
 #include <zlib.h> /* For crc32 */
 
 /* C2.4.7 Multiply and divide */
@@ -469,7 +470,8 @@ void aarch64_cpu_do_interrupt(CPUState *cs)
                   new_el);
     if (qemu_loglevel_mask(CPU_LOG_INT)
         && !excp_is_internal(cs->exception_index)) {
-        qemu_log_mask(CPU_LOG_INT, "...with ESR 0x%" PRIx32 "\n",
+        qemu_log_mask(CPU_LOG_INT, "...with ESR %x/0x%" PRIx32 "\n",
+                      env->exception.syndrome >> ARM_EL_EC_SHIFT,
                       env->exception.syndrome);
     }
 
@@ -535,6 +537,12 @@ void aarch64_cpu_do_interrupt(CPUState *cs)
     aarch64_restore_sp(env, new_el);
 
     env->pc = addr;
-    cs->interrupt_request |= CPU_INTERRUPT_EXITTB;
+
+    qemu_log_mask(CPU_LOG_INT, "...to EL%d PC 0x%" PRIx64 " PSTATE 0x%x\n",
+                  new_el, env->pc, pstate_read(env));
+
+    if (!kvm_enabled()) {
+        cs->interrupt_request |= CPU_INTERRUPT_EXITTB;
+    }
 }
 #endif

diff --git a/target-arm/kvm64.c b/target-arm/kvm64.c
index 771ecdbafe726dd45f10e03c8126c004d91a07a9..bb9531f33c1e07b380bca37b562167b9ae8ba479 100644 (file)
--- a/target-arm/kvm64.c
+++ b/target-arm/kvm64.c
@@ -871,6 +871,7 @@ bool kvm_arm_handle_debug(CPUState *cs, struct kvm_debug_exit_arch *debug_exit)
 {
     int hsr_ec = debug_exit->hsr >> ARM_EL_EC_SHIFT;
     ARMCPU *cpu = ARM_CPU(cs);
+    CPUClass *cc = CPU_GET_CLASS(cs);
     CPUARMState *env = &cpu->env;
 
     /* Ensure PC is synchronised */
@@ -881,7 +882,14 @@ bool kvm_arm_handle_debug(CPUState *cs, struct kvm_debug_exit_arch *debug_exit)
         if (cs->singlestep_enabled) {
             return true;
         } else {
-            error_report("Came out of SINGLE STEP when not enabled");
+            /*
+             * The kernel should have suppressed the guest's ability to
+             * single step at this point so something has gone wrong.
+             */
+            error_report("%s: guest single-step while debugging unsupported"
+                         " (%"PRIx64", %"PRIx32")\n",
+                         __func__, env->pc, debug_exit->hsr);
+            return false;
         }
         break;
     case EC_AA64_BKPT:
@@ -908,12 +916,14 @@ bool kvm_arm_handle_debug(CPUState *cs, struct kvm_debug_exit_arch *debug_exit)
                      __func__, debug_exit->hsr, env->pc);
     }
 
-    /* If we don't handle this it could be it really is for the
-       guest to handle */
-    qemu_log_mask(LOG_UNIMP,
-                  "%s: re-injecting exception not yet implemented"
-                  " (0x%"PRIx32", %"PRIx64")\n",
-                  __func__, hsr_ec, env->pc);
+    /* If we are not handling the debug exception it must belong to
+     * the guest. Let's re-use the existing TCG interrupt code to set
+     * everything up properly.
+     */
+    cs->exception_index = EXCP_BKPT;
+    env->exception.syndrome = debug_exit->hsr;
+    env->exception.vaddress = debug_exit->far;
+    cc->do_interrupt(cs);
 
     return false;
 }