[Qemu-devel] [PATCH] target-arm: Implement 'int' loglevel

[Peter Maydell <peter.maydell@linaro.org>]

The 'int' loglevel for recording interrupts and exceptions
requires support in the target-specific code. Implement
it for ARM. This improves debug logging in some situations
that were otherwise pretty opaque, such as when we fault
trying to execute at an exception vector address, which
would otherwise cause an infinite loop of taking exceptions
without any indication in the debug log of what was going on.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
An infinite loop of exceptions now comes out in the trace like this:

Taking exception 3 [Prefetch Abort]
...with IFSR 0xd IFAR 0x201043c
Taking exception 3 [Prefetch Abort]
...with IFSR 0xd IFAR 0xc
Taking exception 3 [Prefetch Abort]
...with IFSR 0xd IFAR 0xc
Taking exception 3 [Prefetch Abort]
...with IFSR 0xd IFAR 0xc


 target-arm/helper.c |   42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/target-arm/helper.c b/target-arm/helper.c
index 3c57558..c221e76 100644
--- a/target-arm/helper.c
+++ b/target-arm/helper.c
@@ -2228,6 +2228,37 @@ static void do_v7m_exception_exit(CPUARMState *env)
        pointer.  */
 }
 
+/* Exception names for debug logging; note that not all of these
+ * precisely correspond to architectural exceptions.
+ */
+static const char *excnames[] = {
+    [EXCP_UDEF] = "Undefined Instruction",
+    [EXCP_SWI] = "SVC",
+    [EXCP_PREFETCH_ABORT] = "Prefetch Abort",
+    [EXCP_DATA_ABORT] = "Data Abort",
+    [EXCP_IRQ] = "IRQ",
+    [EXCP_FIQ] = "FIQ",
+    [EXCP_BKPT] = "Breakpoint",
+    [EXCP_EXCEPTION_EXIT] = "QEMU v7M exception exit",
+    [EXCP_KERNEL_TRAP] = "QEMU intercept of kernel commpage",
+    [EXCP_STREX] = "QEMU intercept of STREX",
+};
+
+static inline void arm_log_exception(int idx)
+{
+    if (qemu_loglevel_mask(CPU_LOG_INT)) {
+        const char *exc = NULL;
+
+        if (idx >= 0 && idx < ARRAY_SIZE(excnames)) {
+            exc = excnames[idx];
+        }
+        if (!exc) {
+            exc = "unknown";
+        }
+        qemu_log_mask(CPU_LOG_INT, "Taking exception %d [%s]\n", idx, exc);
+    }
+}
+
 void arm_v7m_cpu_do_interrupt(CPUState *cs)
 {
     ARMCPU *cpu = ARM_CPU(cs);
@@ -2236,6 +2267,8 @@ void arm_v7m_cpu_do_interrupt(CPUState *cs)
     uint32_t lr;
     uint32_t addr;
 
+    arm_log_exception(env->exception_index);
+
     lr = 0xfffffff1;
     if (env->v7m.current_sp)
         lr |= 4;
@@ -2265,6 +2298,7 @@ void arm_v7m_cpu_do_interrupt(CPUState *cs)
             if (nr == 0xab) {
                 env->regs[15] += 2;
                 env->regs[0] = do_arm_semihosting(env);
+                qemu_log_mask(CPU_LOG_INT, "...handled as semihosting call\n");
                 return;
             }
         }
@@ -2318,6 +2352,8 @@ void arm_cpu_do_interrupt(CPUState *cs)
 
     assert(!IS_M(env));
 
+    arm_log_exception(env->exception_index);
+
     /* TODO: Vectored interrupt controller.  */
     switch (env->exception_index) {
     case EXCP_UDEF:
@@ -2345,6 +2381,7 @@ void arm_cpu_do_interrupt(CPUState *cs)
                     || (mask == 0xab && env->thumb))
                   && (env->uncached_cpsr & CPSR_M) != ARM_CPU_MODE_USR) {
                 env->regs[0] = do_arm_semihosting(env);
+                qemu_log_mask(CPU_LOG_INT, "...handled as semihosting call\n");
                 return;
             }
         }
@@ -2362,18 +2399,23 @@ void arm_cpu_do_interrupt(CPUState *cs)
                   && (env->uncached_cpsr & CPSR_M) != ARM_CPU_MODE_USR) {
                 env->regs[15] += 2;
                 env->regs[0] = do_arm_semihosting(env);
+                qemu_log_mask(CPU_LOG_INT, "...handled as semihosting call\n");
                 return;
             }
         }
         env->cp15.c5_insn = 2;
         /* Fall through to prefetch abort.  */
     case EXCP_PREFETCH_ABORT:
+        qemu_log_mask(CPU_LOG_INT, "...with IFSR 0x%x IFAR 0x%x\n",
+                      env->cp15.c5_insn, env->cp15.c6_insn);
         new_mode = ARM_CPU_MODE_ABT;
         addr = 0x0c;
         mask = CPSR_A | CPSR_I;
         offset = 4;
         break;
     case EXCP_DATA_ABORT:
+        qemu_log_mask(CPU_LOG_INT, "...with DFSR 0x%x DFAR 0x%x\n",
+                      env->cp15.c5_data, env->cp15.c6_data);
         new_mode = ARM_CPU_MODE_ABT;
         addr = 0x10;
         mask = CPSR_A | CPSR_I;
-- 
1.7.9.5