Handle UNW_X86_64_RIP in Registers_x86_64

[laplab]

Summary

We use LLVM libunwind in query profiler of ClickHouse DBMS.

Basically server is interrupted by signal with high frequency and libunwind API is called in signal handler. During the development we noticed that at random time points server aborts with message:

libunwind: getRegister ../contrib/libunwind/src/Registers.hpp:379 - unsupported x86_64 register

Further investigation with gdb has shown that libunwind tries to get register #16 (numeration starts from zero) which is RIP on x86_64.
We have tried to localise the problem and provide a minimum example, but there were no pattern in these errors.
After reading some code around Registers.hpp it turned out that UNW_X86_64_RIP is not handled in switches of Registers_x86_64 which we believe is a problem. This diff adds handling of this option.
We have applied this change to our fork of libunwind and error has never repeated again.

[ldionne]

I don't know that code, however it does look strange to me that we have both UNW_X86_64_RIP and UNW_REG_IP to represent rip in the first place.

I can't add reviewers myself for some reason, but I think @mstorsjo would be a good start to look at this based on prior commit history.

[mstorsjo]

I don't really know this either, but @compnerd and/or @rnk might. It looks straightforward, but I don't know if the rip register is special somehow in dwarf.

[mstorsjo]

@joerg might also know

[joerg]

It would be interesting to get an actual backtrace. It should not be a DWARF register number, but it might be from a direct caller of the unw interface.

[mbautin]

We are also running into this issue when building YugabyteDB with Clang 12 with AddressSanitizer instrumentation enabled: https://github.com/yugabyte/yugabyte-db/issues/7092

[MaskRay]

Fixed by D107919, closing

src/Registers.hpp

 
 inline bool Registers_x86_64::validRegister(int regNum) const {
   if (regNum == UNW_REG_IP)
     return true;
   if (regNum == UNW_REG_SP)
     return true;
   if (regNum < 0)
     return false;
-  if (regNum > 15)
+  if (regNum > 16)
     return false;
   return true;
 }
 
 inline uint64_t Registers_x86_64::getRegister(int regNum) const {
   switch (regNum) {
   case UNW_REG_IP:
     return _registers.__rip;
inline uint64_t Registers_x86_64::getRegister(int regNum) const {
   case UNW_X86_64_R12:
     return _registers.__r12;
   case UNW_X86_64_R13:
     return _registers.__r13;
   case UNW_X86_64_R14:
     return _registers.__r14;
   case UNW_X86_64_R15:
     return _registers.__r15;
+  case UNW_X86_64_RIP:
+    return _registers.__rip;
   }
   _LIBUNWIND_ABORT("unsupported x86_64 register");
 }
 
 inline void Registers_x86_64::setRegister(int regNum, uint64_t value) {
   switch (regNum) {
   case UNW_REG_IP:
     _registers.__rip = value;
case UNW_X86_64_R13:
     _registers.__r13 = value;
     return;
   case UNW_X86_64_R14:
     _registers.__r14 = value;
     return;
   case UNW_X86_64_R15:
     _registers.__r15 = value;
     return;
+  case UNW_X86_64_RIP:
+    _registers.__rip = value;
+    return;
   }
   _LIBUNWIND_ABORT("unsupported x86_64 register");
 }
 
 inline const char *Registers_x86_64::getRegisterName(int regNum) {
   switch (regNum) {
   case UNW_REG_IP:
     return "rip";
inline const char *Registers_x86_64::getRegisterName(int regNum) {
   case UNW_X86_64_R12:
     return "r12";
   case UNW_X86_64_R13:
     return "r13";
   case UNW_X86_64_R14:
     return "r14";
   case UNW_X86_64_R15:
     return "r15";
+  case UNW_X86_64_RIP:
+    return "rip";
   case UNW_X86_64_XMM0:
     return "xmm0";
   case UNW_X86_64_XMM1:
     return "xmm1";
   case UNW_X86_64_XMM2:
     return "xmm2";
   case UNW_X86_64_XMM3:
     return "xmm3";