- Teach the LLVM-derived unwinder about the DWARF pseudo-registers defined

by GCC for MIPS to hold the MDHI and MDLO registers, as well as the return
  address where the signal trampoline will resume.  XXX Same treatment is
  needed for MIPS64, but not done as part of this commit.
- In the MIPS validFloatVectorRegister(), compare against the internal
  register numbers, not the DWARF register numbers.

sys/lib/libunwind/Registers.hpp

@@ -936,20 +936,29 @@ enum {
   DWARF_MIPS_R31 = 31,
   DWARF_MIPS_F0 = 32,
   DWARF_MIPS_F31 = 63,
+  // DWARF Pseudo-registers used by GCC on MIPS for MD{HI,LO} and
+  // signal handler return address.
+  DWARF_MIPS_MDHI = 64,
+  DWARF_MIPS_MDLO = 65,
+  DWARF_MIPS_SIGRETURN = 66,
 
   REGNO_MIPS_PC = 0,
   REGNO_MIPS_R1 = 0,
   REGNO_MIPS_R29 = 29,
   REGNO_MIPS_R31 = 31,
   REGNO_MIPS_F0 = 33,
-  REGNO_MIPS_F31 = 64
+  REGNO_MIPS_F31 = 64,
+  // these live in other_reg[]
+  REGNO_MIPS_MDHI = 65,
+  REGNO_MIPS_MDLO = 66,
+  REGNO_MIPS_SIGRETURN = 67
 };
 
 class Registers_MIPS {
 public:
   enum {
-    LAST_REGISTER = REGNO_MIPS_F31,
-    LAST_RESTORE_REG = REGNO_MIPS_F31,
+    LAST_REGISTER = REGNO_MIPS_SIGRETURN,
+    LAST_RESTORE_REG = REGNO_MIPS_SIGRETURN,
     RETURN_OFFSET = 0,
     RETURN_MASK = 0,
   };
@@ -961,20 +970,28 @@ public:
       return REGNO_MIPS_R1 + (num - DWARF_MIPS_R1);
     if (num >= DWARF_MIPS_F0 && num <= DWARF_MIPS_F31)
       return REGNO_MIPS_F0 + (num - DWARF_MIPS_F0);
+    if (num >= DWARF_MIPS_MDHI && num <= DWARF_MIPS_SIGRETURN)
+      return REGNO_MIPS_MDHI + (num - DWARF_MIPS_MDHI);
     return LAST_REGISTER + 1;
   }
 
   bool validRegister(int num) const {
-    return num >= REGNO_MIPS_PC && num <= REGNO_MIPS_R31;
+    return (num >= REGNO_MIPS_PC && num <= REGNO_MIPS_R31) ||
+      (num >= REGNO_MIPS_MDHI && num <= REGNO_MIPS_SIGRETURN);
   }
 
   uint64_t getRegister(int num) const {
     assert(validRegister(num));
+    if (num >= REGNO_MIPS_MDHI && num <= REGNO_MIPS_SIGRETURN)
+      return other_reg[num - REGNO_MIPS_MDHI];
     return reg[num];
   }
 
   void setRegister(int num, uint64_t value) {
     assert(validRegister(num));
+    if (num >= REGNO_MIPS_MDHI && num <= REGNO_MIPS_SIGRETURN)
+      other_reg[num - REGNO_MIPS_MDHI] = value;
+    else
       reg[num] = value;
   }
 
@@ -987,7 +1004,7 @@ public:
   void setSP(uint64_t value) { reg[REGNO_MIPS_R29] = value; }
 
   bool validFloatVectorRegister(int num) const {
-    return num >= DWARF_MIPS_F0 && num <= DWARF_MIPS_F31;
+    return num >= REGNO_MIPS_F0 && num <= REGNO_MIPS_F31;
   }
 
   void copyFloatVectorRegister(int num, uint64_t addr_) {
@@ -1001,6 +1018,7 @@ public:
 private:
   uint32_t reg[REGNO_MIPS_R31 + 1];
   uint64_t fpreg[32];
+  uint32_t other_reg[3];
 };
 
 enum {