[libFuzzer] Ignore synthetic exceptions on Fuchsia

Fuchsia has several exceptions which are merely informational and should
not be treated as crashes. This patch puts logic that read from the
exception port and handled the exception in a loop, and ignores
non-exceptions and informational exceptions.

Patch By: aarongreen

Differential Revision: https://reviews.llvm.org/D62226

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@361407 91177308-0d34-0410-b5e6-96231b3b80d8

lib/fuzzer/FuzzerUtilFuchsia.cpp

@@ -13,6 +13,7 @@
 
 #include "FuzzerInternal.h"
 #include "FuzzerUtil.h"
+#include <cassert>
 #include <cerrno>
 #include <cinttypes>
 #include <cstdint>
@@ -232,57 +233,72 @@ void CrashHandler(zx_handle_t *Event) {
   ExitOnErr(_zx_object_signal(*Event, 0, ZX_USER_SIGNAL_0),
             "_zx_object_signal");
 
-  zx_port_packet_t Packet;
-  ExitOnErr(_zx_port_wait(Port.Handle, ZX_TIME_INFINITE, &Packet),
-            "_zx_port_wait");
-
-  // At this point, we want to get the state of the crashing thread, but
-  // libFuzzer and the sanitizers assume this will happen from that same thread
-  // via a POSIX signal handler. "Resurrecting" the thread in the middle of the
-  // appropriate callback is as simple as forcibly setting the instruction
-  // pointer/program counter, provided we NEVER EVER return from that function
-  // (since otherwise our stack will not be valid).
-  ScopedHandle Thread;
-  ExitOnErr(_zx_object_get_child(Self, Packet.exception.tid,
-                                 ZX_RIGHT_SAME_RIGHTS, &Thread.Handle),
-            "_zx_object_get_child");
-
-  zx_thread_state_general_regs_t GeneralRegisters;
-  ExitOnErr(_zx_thread_read_state(Thread.Handle, ZX_THREAD_STATE_GENERAL_REGS,
-                                  &GeneralRegisters, sizeof(GeneralRegisters)),
-            "_zx_thread_read_state");
-
-  // To unwind properly, we need to push the crashing thread's register state
-  // onto the stack and jump into a trampoline with CFI instructions on how
-  // to restore it.
+  // This thread lives as long as the process in order to keep handling
+  // crashes.  In practice, the first crashed thread to reach the end of the
+  // StaticCrashHandler will end the process.
+  while (true) {
+    zx_port_packet_t Packet;
+    ExitOnErr(_zx_port_wait(Port.Handle, ZX_TIME_INFINITE, &Packet),
+              "_zx_port_wait");
+
+    // Ignore informational synthetic exceptions.
+    assert(ZX_PKT_IS_EXCEPTION(Packet.type));
+    if (ZX_EXCP_THREAD_STARTING == Packet.type ||
+        ZX_EXCP_THREAD_EXITING == Packet.type ||
+        ZX_EXCP_PROCESS_STARTING == Packet.type) {
+      continue;
+    }
+
+    // At this point, we want to get the state of the crashing thread, but
+    // libFuzzer and the sanitizers assume this will happen from that same
+    // thread via a POSIX signal handler. "Resurrecting" the thread in the
+    // middle of the appropriate callback is as simple as forcibly setting the
+    // instruction pointer/program counter, provided we NEVER EVER return from
+    // that function (since otherwise our stack will not be valid).
+    ScopedHandle Thread;
+    ExitOnErr(_zx_object_get_child(Self, Packet.exception.tid,
+                                   ZX_RIGHT_SAME_RIGHTS, &Thread.Handle),
+              "_zx_object_get_child");
+
+    zx_thread_state_general_regs_t GeneralRegisters;
+    ExitOnErr(_zx_thread_read_state(Thread.Handle, ZX_THREAD_STATE_GENERAL_REGS,
+                                    &GeneralRegisters,
+                                    sizeof(GeneralRegisters)),
+              "_zx_thread_read_state");
+
+    // To unwind properly, we need to push the crashing thread's register state
+    // onto the stack and jump into a trampoline with CFI instructions on how
+    // to restore it.
 #if defined(__x86_64__)
-  uintptr_t StackPtr =
-      (GeneralRegisters.rsp - (128 + sizeof(GeneralRegisters))) &
-      -(uintptr_t)16;
-  __unsanitized_memcpy(reinterpret_cast<void *>(StackPtr), &GeneralRegisters,
-         sizeof(GeneralRegisters));
-  GeneralRegisters.rsp = StackPtr;
-  GeneralRegisters.rip = reinterpret_cast<zx_vaddr_t>(CrashTrampolineAsm);
+    uintptr_t StackPtr =
+        (GeneralRegisters.rsp - (128 + sizeof(GeneralRegisters))) &
+        -(uintptr_t)16;
+    __unsanitized_memcpy(reinterpret_cast<void *>(StackPtr), &GeneralRegisters,
+                         sizeof(GeneralRegisters));
+    GeneralRegisters.rsp = StackPtr;
+    GeneralRegisters.rip = reinterpret_cast<zx_vaddr_t>(CrashTrampolineAsm);
 
 #elif defined(__aarch64__)
-  uintptr_t StackPtr =
-      (GeneralRegisters.sp - sizeof(GeneralRegisters)) & -(uintptr_t)16;
-  __unsanitized_memcpy(reinterpret_cast<void *>(StackPtr), &GeneralRegisters,
-                       sizeof(GeneralRegisters));
-  GeneralRegisters.sp = StackPtr;
-  GeneralRegisters.pc = reinterpret_cast<zx_vaddr_t>(CrashTrampolineAsm);
+    uintptr_t StackPtr =
+        (GeneralRegisters.sp - sizeof(GeneralRegisters)) & -(uintptr_t)16;
+    __unsanitized_memcpy(reinterpret_cast<void *>(StackPtr), &GeneralRegisters,
+                         sizeof(GeneralRegisters));
+    GeneralRegisters.sp = StackPtr;
+    GeneralRegisters.pc = reinterpret_cast<zx_vaddr_t>(CrashTrampolineAsm);
 
 #else
 #error "Unsupported architecture for fuzzing on Fuchsia"
 #endif
 
-  // Now force the crashing thread's state.
-  ExitOnErr(_zx_thread_write_state(Thread.Handle, ZX_THREAD_STATE_GENERAL_REGS,
-                                   &GeneralRegisters, sizeof(GeneralRegisters)),
-            "_zx_thread_write_state");
+    // Now force the crashing thread's state.
+    ExitOnErr(
+        _zx_thread_write_state(Thread.Handle, ZX_THREAD_STATE_GENERAL_REGS,
+                               &GeneralRegisters, sizeof(GeneralRegisters)),
+        "_zx_thread_write_state");
 
-  ExitOnErr(_zx_task_resume_from_exception(Thread.Handle, Port.Handle, 0),
-            "_zx_task_resume_from_exception");
+    ExitOnErr(_zx_task_resume_from_exception(Thread.Handle, Port.Handle, 0),
+              "_zx_task_resume_from_exception");
+  }
 }
 
 } // namespace