[sanitizers] read/write page fault detection on mac.

[aizatsky]

nit

[eugenis]

LGTM

[vsk]

Hi Mike, some of our internal bots are having an issue with this commit:

error: no member named '__err' in '__darwin_arm_exception_state'
  return ucontext->uc_mcontext->__es.__err & 2 /*T_PF_WRITE*/ ? WRITE : READ;

I'd really appreciate it if you could shed some light on this. I see two definitions of this structure in the OS, and neither contain '__err'. Can you share which OS you built this code against?

[aizatsky]

Vedant,

I believe it is 10.11 on Intel. This could be CPU difference. I'll try to
add appropriate ifdefs tomorrow.

[mehdi_amini]

I'll revert in the meantime. Feel free to reapply with the fix.

For reference from what I see here: http://opensource.apple.com//source/cctools/cctools-836/include/mach/arm/_structs.h this was hitting:

#define _STRUCT_ARM_EXCEPTION_STATE	struct __darwin_arm_exception_state
_STRUCT_ARM_EXCEPTION_STATE
{
	__uint32_t	__exception; /* number of arm exception taken */
	__uint32_t	__fsr; /* Fault status */
	__uint32_t	__far; /* Virtual Fault Address */
};

[aizatsky]

Is there a kernel source as well for mac on aarch64? I'm trying to determine if illegal write or read has happened. Would be bad to leave aarch out of the implementation.

[vsk]

Do the xnu sources here help? The latest publicly-available one appears to be xnu-3248.20.55 (http://opensource.apple.com/source/xnu/).

[aizatsky]

New review with feature enabled only on intel: http://reviews.llvm.org/D19561

I can't find aarch64 support in published xnu sources.

lib/sanitizer_common/sanitizer_mac.cc

#endif
   BlockingMutexLock l(&syslog_lock);
   if (common_flags()->log_to_syslog)
     WriteToSyslog(buffer);
 
   // The report is added to CrashLog as part of logging all of Printf output.
 }
 
 SignalContext::WriteFlag SignalContext::GetWriteFlag(void *context) {
-  return UNKNOWN;  // FIXME: implement this.
+  ucontext_t *ucontext = static_cast<ucontext_t*>(context);
+  return ucontext->uc_mcontext->__es.__err & 2 /*T_PF_WRITE*/ ? WRITE : READ;
 }
 
 void GetPcSpBp(void *context, uptr *pc, uptr *sp, uptr *bp) {
   ucontext_t *ucontext = (ucontext_t*)context;
 # if defined(__aarch64__)
   *pc = ucontext->uc_mcontext->__ss.__pc;
 #   if defined(__IPHONE_8_0) && __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_8_0
   *bp = ucontext->uc_mcontext->__ss.__fp;

test/asan/TestCases/Posix/segv_read_write.c

int main(int argc, char **argv) {
   void *volatile p =
       mmap(nullptr, 4096, PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
   munmap(p, 4096);
   if (argc == 1)
     Read((int *)p);
   else
     Write((int *)p);
 }
-// READ: AddressSanitizer: SEGV on unknown address
+// READ: AddressSanitizer: SEGV on unknown address11
 // READ: The signal is caused by a READ memory access.
 // WRITE: AddressSanitizer: SEGV on unknown address
 // WRITE: The signal is caused by a WRITE memory access.