x86: Optionally dump code bytes on cpu_dump_state

Introduce the cpu_dump_state flag CPU_DUMP_CODE and implement it for
x86. This writes out the code bytes around the current instruction
pointer. Make use of this feature in KVM to help debugging fatal vm
exits.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>

cpu-all.h

@@ -765,6 +765,8 @@ int page_check_range(target_ulong start, target_ulong len, int flags);
 CPUState *cpu_copy(CPUState *env);
 CPUState *qemu_get_cpu(int cpu);
 
+#define CPU_DUMP_CODE 0x00010000
+
 void cpu_dump_state(CPUState *env, FILE *f, fprintf_function cpu_fprintf,
                     int flags);
 void cpu_dump_statistics(CPUState *env, FILE *f, fprintf_function cpu_fprintf,

kvm-all.c

@@ -832,7 +832,7 @@ static int kvm_handle_internal_error(CPUState *env, struct kvm_run *run)
     if (run->internal.suberror == KVM_INTERNAL_ERROR_EMULATION) {
         fprintf(stderr, "emulation failure\n");
         if (!kvm_arch_stop_on_emulation_error(env)) {
-            cpu_dump_state(env, stderr, fprintf, 0);
+            cpu_dump_state(env, stderr, fprintf, CPU_DUMP_CODE);
             return 0;
         }
     }
@@ -994,7 +994,7 @@ int kvm_cpu_exec(CPUState *env)
     } while (ret > 0);
 
     if (ret < 0) {
-        cpu_dump_state(env, stderr, fprintf, 0);
+        cpu_dump_state(env, stderr, fprintf, CPU_DUMP_CODE);
         vm_stop(0);
         env->exit_request = 1;
     }

target-i386/helper.c

@@ -249,6 +249,9 @@ done:
     cpu_fprintf(f, "\n");
 }
 
+#define DUMP_CODE_BYTES_TOTAL    50
+#define DUMP_CODE_BYTES_BACKWARD 20
+
 void cpu_dump_state(CPUState *env, FILE *f, fprintf_function cpu_fprintf,
                     int flags)
 {
@@ -434,6 +437,24 @@ void cpu_dump_state(CPUState *env, FILE *f, fprintf_function cpu_fprintf,
                 cpu_fprintf(f, " ");
         }
     }
+    if (flags & CPU_DUMP_CODE) {
+        target_ulong base = env->segs[R_CS].base + env->eip;
+        target_ulong offs = MIN(env->eip, DUMP_CODE_BYTES_BACKWARD);
+        uint8_t code;
+        char codestr[3];
+
+        cpu_fprintf(f, "Code=");
+        for (i = 0; i < DUMP_CODE_BYTES_TOTAL; i++) {
+            if (cpu_memory_rw_debug(env, base - offs + i, &code, 1, 0) == 0) {
+                snprintf(codestr, sizeof(codestr), "%02x", code);
+            } else {
+                snprintf(codestr, sizeof(codestr), "??");
+            }
+            cpu_fprintf(f, "%s%s%s%s", i > 0 ? " " : "",
+                        i == offs ? "<" : "", codestr, i == offs ? ">" : "");
+        }
+        cpu_fprintf(f, "\n");
+    }
 }
 
 /***********************************************************/