[asan] Add a "dump_registers" flag to print out CPU registers after a SIGSEGV

[kubamracek]

Summary

This patch adds a new ASan flag, dump_registers (off by default), which after a SIGSEGV prints out all CPU registers. These are available in the signal handler context. The use case is when you're not running under the debugger, and you end up with a SIGSEGV ASan report, which doesn't contain much information – knowing the register values can be helpful here. Another interesting case is on x86_64, where if you fault on a non-canonical address (e.g. 0xdeaddeaddeaddead), this address is not propagated into siginfo->si_addr and is only located in one of the registers.

I only implemented the Darwin part and left the other functions (Linux, Windows) empty in hopes that some good soul will fill these in :)

[kcc]

Looks good in general, still a few comments

lib/asan/asan_flags.inc

146

Add something like "OSX-only for now"

lib/sanitizer_common/sanitizer_linux.cc

1102

Add something like "Printf("DumpAllRegisters is not implemented on this platform");

same below.

lib/sanitizer_common/sanitizer_mac.cc

438

#undef the macros at the end of the function

test/asan/TestCases/Darwin/dump_registers.cc

1 ↗

(On Diff #30179)

I wonder if you can move this test one level up (not Darwin-specific) and restrict it for Darwin.

[glider]

LGTM once comments from Kostya are fixed.

[kubamracek]

Addressing review comments.

I wonder if you can move this test one level up (not Darwin-specific) and restrict it for Darwin.

Hm, it doesn't seem so. REQUIRES: Darwin doesn't work. I could add XFAIL: Linux and XFAIL: FreeBSD...

Also, what do you think about having this on by default?

[kcc]

In D11365#208870, @kubabrecka wrote:

Addressing review comments.

I wonder if you can move this test one level up (not Darwin-specific) and restrict it for Darwin.

Hm, it doesn't seem so. REQUIRES: Darwin doesn't work. I could add XFAIL: Linux and XFAIL: FreeBSD...

Unless Alexey can suggest how to require Darwin, add a bunch of XFAILs.

Also, what do you think about having this on by default?

I don't mind at all, good idea.

[kubamracek]

Added the XFAILs. Turning the flag on by default.

[samsonov]

lib/sanitizer_common/sanitizer_linux.cc

1102

IMO you should either remove this line to not litter the output, or avoid enabling dump_registers by default...

lib/sanitizer_common/sanitizer_win.cc

663

ditto

[kubamracek]

IMO you should either remove this line to not litter the output, or avoid enabling dump_registers by default...

Makes sense. In that case it seems to me that it's better to just drop the flag altogether, and simply print this when it's implemented (OS X only for now).

[kcc]

I'd keep the flag, just make it on by default.

[kubamracek]

Addressing review comments (keeping the flag, on by default, removing output when not implemented).

lib/asan/asan_flags.inc

           "have different sizes")
 ASAN_FLAG(bool, dump_instruction_bytes, false,
           "If true, dump 16 bytes starting at the instruction that caused SEGV")
+ASAN_FLAG(bool, dump_registers, true,
+          "If true, dump values of CPU registers when SEGV happens. Only "
+          "available on OS X for now.")
 ASAN_FLAG(const char *, suppressions, "", "Suppressions file name.")

lib/asan/asan_report.cc

   Report("%s", str.data());
 }
 
+void MaybeDumpRegisters(const SignalContext &sig) {
+  if (!flags()->dump_registers) return;
+  sig.DumpAllRegisters();
+}
+
 static void PrintShadowMemoryForAddress(uptr addr) {
   if (!AddrIsInMem(addr)) return;
   uptr shadow_addr = MemToShadow(addr);

   GET_STACK_TRACE_SIGNAL(sig);
   stack.Print();
   MaybeDumpInstructionBytes(sig.pc);
+  MaybeDumpRegisters(sig);
   Printf("AddressSanitizer can not provide additional info.\n");
   ReportErrorSummary("SEGV", &stack);
 }

lib/sanitizer_common/sanitizer_common.h

       context(context), addr(addr), pc(pc), sp(sp), bp(bp) {
   }
 
+  void DumpAllRegisters() const;
+
   // Creates signal context in a platform-specific manner.
   static SignalContext Create(void *siginfo, void *context);
 };

lib/sanitizer_common/sanitizer_linux.cc

 #endif
 }
 
+void SignalContext::DumpAllRegisters() const {
+  // FIXME: Implement this.
+}
+
 }  // namespace __sanitizer
 
 #endif  // SANITIZER_FREEBSD || SANITIZER_LINUX

lib/sanitizer_common/sanitizer_mac.cc

 # endif
 }
 
+void SignalContext::DumpAllRegisters() const {
+  Report("Register values:\n");
+
+  ucontext_t *ucontext = (ucontext_t*)context;
+# define DUMPREG64(r) \
+    Printf("%s = 0x%016llx  ", #r, ucontext->uc_mcontext->__ss.__ ## r);
+# define DUMPREG32(r) \
+    Printf("%s = 0x%08x  ", #r, ucontext->uc_mcontext->__ss.__ ## r);
+# define DUMPREG_(r)   Printf(" "); DUMPREG(r);
+# define DUMPREG__(r)  Printf("  "); DUMPREG(r);
+# define DUMPREG___(r) Printf("   "); DUMPREG(r);
+
+# if defined(__x86_64__)
+#  define DUMPREG(r) DUMPREG64(r)
+  DUMPREG(rax); DUMPREG(rbx); DUMPREG(rcx); DUMPREG(rdx); Printf("\n");
+  DUMPREG(rdi); DUMPREG(rsi); DUMPREG(rbp); DUMPREG(rsp); Printf("\n");
+  DUMPREG_(r8); DUMPREG_(r9); DUMPREG(r10); DUMPREG(r11); Printf("\n");
+  DUMPREG(r12); DUMPREG(r13); DUMPREG(r14); DUMPREG(r15); Printf("\n");
+# elif defined(__i386__)
+#  define DUMPREG(r) DUMPREG32(r)
+  DUMPREG(eax); DUMPREG(ebx); DUMPREG(ecx); DUMPREG(edx); Printf("\n");
+  DUMPREG(edi); DUMPREG(esi); DUMPREG(ebp); DUMPREG(esp); Printf("\n");
+# elif defined(__aarch64__)
+#  define DUMPREG(r) DUMPREG64(r)
+  DUMPREG_(x[0]); DUMPREG_(x[1]); DUMPREG_(x[2]); DUMPREG_(x[3]); Printf("\n");
+  DUMPREG_(x[4]); DUMPREG_(x[5]); DUMPREG_(x[6]); DUMPREG_(x[7]); Printf("\n");
+  DUMPREG_(x[8]); DUMPREG_(x[9]); DUMPREG(x[10]); DUMPREG(x[11]); Printf("\n");
+  DUMPREG(x[12]); DUMPREG(x[13]); DUMPREG(x[14]); DUMPREG(x[15]); Printf("\n");
+  DUMPREG(x[16]); DUMPREG(x[17]); DUMPREG(x[18]); DUMPREG(x[19]); Printf("\n");
+  DUMPREG(x[20]); DUMPREG(x[21]); DUMPREG(x[22]); DUMPREG(x[23]); Printf("\n");
+  DUMPREG(x[24]); DUMPREG(x[25]); DUMPREG(x[26]); DUMPREG(x[27]); Printf("\n");
+  DUMPREG(x[28]); DUMPREG___(fp); DUMPREG___(lr); DUMPREG___(sp); Printf("\n");
+# elif defined(__arm__)
+#  define DUMPREG(r) DUMPREG32(r)
+  DUMPREG_(r[0]); DUMPREG_(r[1]); DUMPREG_(r[2]); DUMPREG_(r[3]); Printf("\n");
+  DUMPREG_(r[4]); DUMPREG_(r[5]); DUMPREG_(r[6]); DUMPREG_(r[7]); Printf("\n");
+  DUMPREG_(r[8]); DUMPREG_(r[9]); DUMPREG(r[10]); DUMPREG(r[11]); Printf("\n");
+  DUMPREG(r[12]); DUMPREG___(sp); DUMPREG___(lr); DUMPREG___(pc); Printf("\n");
+# else
+# error "Unknown architecture"
+# endif
+
+# undef DUMPREG64
+# undef DUMPREG32
+# undef DUMPREG_
+# undef DUMPREG__
+# undef DUMPREG___
+# undef DUMPREG
+}
+
 }  // namespace __sanitizer
 
 #endif  // SANITIZER_MAC

lib/sanitizer_common/sanitizer_win.cc

   return SignalContext(context, access_addr, pc, sp, bp);
 }
 
+void SignalContext::DumpAllRegisters() const {
+  // FIXME: Implement this.
+}
+
 uptr ReadBinaryName(/*out*/char *buf, uptr buf_len) {
   // FIXME: Actually implement this function.
   CHECK_GT(buf_len, 0);

test/asan/TestCases/dump_registers.cc

+// Check that ASan dumps the CPU registers on a SIGSEGV.
+
+// RUN: %clangxx_asan %s -o %t
+// RUN: not %run %t 2>&1 | FileCheck %s
+
+// XFAIL: android
+// XFAIL: freebsd
+// XFAIL: linux
+// XFAIL: win32
+
+#include <assert.h>
+#include <stdio.h>
+
+int main() {
+  printf("Hello\n");
+  char *ptr;
+
+  if (sizeof(void *) == 8)
+    ptr = (char *)0x6666666666666666;
+  else if (sizeof(void *) == 4)
+    ptr = (char *)0x55555555;
+  else
+    assert(0 && "Your computer is weird.");
+
+  char c = *ptr;  // BOOM
+  // CHECK: ERROR: AddressSanitizer: SEGV
+  // CHECK: Register values:
+  // CHECK: {{0x55555555|0x6666666666666666}}
+  printf("World\n");
+  return c;
+}