[libunwind][MIPS]: Add support for unwinding in O32 and N64 processes.

[bsdjhb]

Summary

This supports the soft-float ABI only and has been tested with both clang
and gcc on FreeBSD.

[bsdjhb]

I have not managed to get the libunwind tests to run, but I was able to run test C++ programs on FreeBSD for both O32 and N64 that caught exceptions. The first test program just uses _Unwind_Backtrace() with a callback to print out the PC values, throws an integer whose value is output in a catch clause, and finally throws a structure whose members are output in a catch clause. I have also built and run a larger real-world C++ program which makes extensive use of exceptions (gdb) on both O32 and N64.

If desired, I can split the O32 vs N64 into two separate patches. I also have another patchset for MIPS N32 that I will post in a separate review once this one has been reviewed.

[theraven]

Note: My n64 changes (and, by the look of it, the o32 changes) only supported the soft-float ABI and so need a check for defined(__mips_soft_float), and should still #error if we're not saving the floating point registers. We're currently using soft float for CHERI, I wasn't able to test a hard-float version (though it should be fairly trivial to add).

[sdardis]

+CC cfe-commits, -CC llvm-commits.

Some comments inlined.

I've managed to run the test-suite on one of my machines here and I'm seeing 3 failures:

libunwind :: libunwind_01.pass.cpp
libunwind :: libunwind_02.pass.cpp
libunwind :: unw_getcontext.pass.cpp

This is with a GCC toolchain, 6.3. Did you test with clang?

include/__libunwind_config.h

67

Can you avoid using the mips_o32 macro and instead use defined(mips__) && _MIPS_SIM == _ABIO32 ?

It appears the mips_o32 is a FreeBSD specific macro. Also, test for mips_soft_float .

72

Likewise "defined(mips) && _MIPS_SIM == _ABI64 && __mips_soft_float"

src/UnwindRegistersRestore.S

527

defined(mips_o32) -> defined(mips__) && _MIPS_SIM == _ABIO32

535

Prefix this with:

.set push
.set nomacro

Also, the assembler directives should come after the function declaration / defines.

574

.set pop

575

defined(mips) && _MIPS_SIM == _ABI64

585

See my comments on the o32 assembly.

src/UnwindRegistersSave.S

119

See my previous comments about this preprocessor macro.

130

Wrap this with

.set push
.set noat
.set nomacro

149

and:

.set pop

150

Again, see my previous comments on this preprocessor define.

161

Wrap this with

.set push
.set noat
.set nomacro

180

.set pop

src/libunwind.cpp

67

The MIPS architecture is not supported with this ABI and environment!

[bsdjhb]

• Fixes from review feedback.

[bsdjhb]

I have only tested this (test programs as mentioned earlier) with clang 5.0.0 (with a few patches) on o32 and n64. I am in the process of performing the same tests with GCC 6.3.0. I will also spend some time figuring out how to cross-build libunwind tests and run them inside of a qemu instance.

[bsdjhb]

FYI, I was able to do simple testing (C++ programs throwing exceptions) using GCC 6.3 to compile a FreeBSD userland for both O32 and N64. Still working on cross-compiling LLVM so I can run the tests under qemu.

[bsdjhb]

I keep running into issues trying to cross-build LLVM (it keeps wanting to use /usr/bin/cc or host libraries even though cross-compiling is enabled). I wonder if the failures you saw Simon might be due to https://bugs.llvm.org/show_bug.cgi?id=33858? Could you try applying the patch from D37484 along with this patchset to see if it fixes the test failures for you?

[sdardis]

Thanks for the pointer to that patch, I'll take a look tomorrow.

src/UnwindRegistersRestore.S

527

Needs checking for soft-float.

578

Needs checking for soft-float.

src/UnwindRegistersSave.S

119

Needs checking for soft-float.

154

Needs checking for soft-float.

[bsdjhb]

• Add more soft-float checks.

[sdardis]

I have tested this on one of my machines after removing the checks for soft float (my debian install doesn't have the necessary headers for soft-float). With the patch you've pointed out and my inline comments addressed (bar the HI / LO register comments), it passes the supplied test suite.

Can you change the checks for ABI from '_MIPS_SIM == $ABI' to 'defined($ABI)'? I mistakenly assumed they were always defined and that _MIPS_SIM was defined to be one of them but they are only defined when that particular ABI is being used.

include/libunwind.h

601

Requires HI / LO registers.

src/Registers.hpp

2074

This appears to be missing the HI / LO registers.

2099

FIXME: Hard float, DSP accumulator registers, MSA registers

src/UnwindRegistersSave.S

149–151

Move the last store out of the delay slot and put 'or $2, $zero, $zero' in the delay slot to return UNW_ESUCCESS.

184–186

Move the last store out of the delay slot and put 'or $2, $zero, $zero' in the delay slot to return UNW_ESUCCESS.

[sdardis]

Marking this as changes required to clear up my review queue - no further comments.

[bsdjhb]

• Check _ABI* rather than _MIPS_SIM.
• Save and restore lo/hi.
• Expand FIXME comment for more missing registers.
• Return UNW_SUCCESS from unw_getcontext().
• Use correct DWARF numbers for hi and lo and put hi first.
• Bump highest DWARF number for hi and lo.

[sdardis]

Two last inlined comments and I think that's everything. @compnerd Have I missed anything?

src/UnwindRegistersSave.S

129

After looking at another implementation of libunwind and the other platforms that are supported, it seems to me that we need to save all the registers.

171

Similarly here as well.

[bsdjhb]

• Save all of the general purpose registers.

[bsdjhb]

src/UnwindRegistersSave.S

129

I was about to ask if that would be better as well.

[bsdjhb]

Ping?

[bsdjhb]

• Rebase for recent change to MAX_REGISTER meaning.

[compnerd]

include/__libunwind_config.h

76

Can we sink the two cases into the __mips__ case? Something like:

#if defined(__mips__)
# if defined(_ABIO32)
# elif defined(_ABIO64)
# elif defined(_ABIN32)
# elif defined(_ABI64)
# else
#   error "unknown MIPS ABI"
# endif
#else

src/Registers.hpp

2063

I believe we have a macro for this.

[bsdjhb]

• Rebase on more MAX_REGISTER changes.
• Use macro for lastDwarfRegisterNumber.
• Move MIPS ABI constants under a single #ifdef mips.

[mstorsjo]

Just a heads up WRT this patch; we're discussing changing the size of unw_word_t to match uintptr_t in D39365. Does that break anything for your case? It shouldn't affect what's stored in the Register class, only pointers in the unw_proc_info_t struct. Not sure which patch will get completed/merged first though.

[bsdjhb]

In D38110#910526, @mstorsjo wrote:

Just a heads up WRT this patch; we're discussing changing the size of unw_word_t to match uintptr_t in D39365. Does that break anything for your case? It shouldn't affect what's stored in the Register class, only pointers in the unw_proc_info_t struct. Not sure which patch will get completed/merged first though.

Yes, I saw that. It will probably cause some breakage for the cursor size depending on which path (uint64_t always vs uintptr_t). I'm not quite sure which of those approaches is more correct to be honest. I also have an N32 patch in review but will wait until this one is finally committed before updating that further.

[bsdjhb]

• Rebase.
• Update O32 cursor size after unw_word_t change.

[bsdjhb]

Ping

[sdardis]

@compnerd, ping?

[bsdjhb]

Ping @compnerd, @sdardis

[compnerd]

LGTM if @sdardis is good with it

[sdardis]

LGTM.

include/__libunwind_config.h

 #endif
 
 #define _LIBUNWIND_HIGHEST_DWARF_REGISTER_X86       8
 #define _LIBUNWIND_HIGHEST_DWARF_REGISTER_X86_64    32
 #define _LIBUNWIND_HIGHEST_DWARF_REGISTER_PPC       112
 #define _LIBUNWIND_HIGHEST_DWARF_REGISTER_ARM64     95
 #define _LIBUNWIND_HIGHEST_DWARF_REGISTER_ARM       95
 #define _LIBUNWIND_HIGHEST_DWARF_REGISTER_OR1K      31
+#define _LIBUNWIND_HIGHEST_DWARF_REGISTER_MIPS      65
 
 #if defined(_LIBUNWIND_IS_NATIVE_ONLY)
 # if defined(__i386__)
 #  define _LIBUNWIND_TARGET_I386
 #  define _LIBUNWIND_CONTEXT_SIZE 8
 #  define _LIBUNWIND_CURSOR_SIZE 19
 #  define _LIBUNWIND_HIGHEST_DWARF_REGISTER _LIBUNWIND_HIGHEST_DWARF_REGISTER_X86
 # elif defined(__x86_64__)

 #    define _LIBUNWIND_CURSOR_SIZE 49
 #  endif
 #  define _LIBUNWIND_HIGHEST_DWARF_REGISTER _LIBUNWIND_HIGHEST_DWARF_REGISTER_ARM
 # elif defined(__or1k__)
 #  define _LIBUNWIND_TARGET_OR1K 1
 #  define _LIBUNWIND_CONTEXT_SIZE 16
 #  define _LIBUNWIND_CURSOR_SIZE 28
 #  define _LIBUNWIND_HIGHEST_DWARF_REGISTER _LIBUNWIND_HIGHEST_DWARF_REGISTER_OR1K
+# elif defined(__mips__)
+#  if defined(_ABIO32) && defined(__mips_soft_float)
+#    define _LIBUNWIND_TARGET_MIPS_O32 1
+#    define _LIBUNWIND_CONTEXT_SIZE 18
+#    define _LIBUNWIND_CURSOR_SIZE 29
+#  elif defined(_ABI64) && defined(__mips_soft_float)
+#    define _LIBUNWIND_TARGET_MIPS_N64 1
+#    define _LIBUNWIND_CONTEXT_SIZE 35
+#    define _LIBUNWIND_CURSOR_SIZE 47
+#  else
+#    error "Unsupported MIPS ABI and/or environment"
+#  endif
+#  define _LIBUNWIND_HIGHEST_DWARF_REGISTER _LIBUNWIND_HIGHEST_DWARF_REGISTER_MIPS
 # else
 #  error "Unsupported architecture."
 # endif
 #else // !_LIBUNWIND_IS_NATIVE_ONLY
 # define _LIBUNWIND_TARGET_I386
 # define _LIBUNWIND_TARGET_X86_64 1
 # define _LIBUNWIND_TARGET_PPC 1
 # define _LIBUNWIND_TARGET_AARCH64 1
 # define _LIBUNWIND_TARGET_ARM 1
 # define _LIBUNWIND_TARGET_OR1K 1
+# define _LIBUNWIND_TARGET_MIPS_O32 1
+# define _LIBUNWIND_TARGET_MIPS_N64 1
 # define _LIBUNWIND_CONTEXT_SIZE 128
 # define _LIBUNWIND_CURSOR_SIZE 140
 # define _LIBUNWIND_HIGHEST_DWARF_REGISTER 119
 #endif // _LIBUNWIND_IS_NATIVE_ONLY
 
 #endif // ____LIBUNWIND_CONFIG_H__

include/libunwind.h

enum {
   UNW_OR1K_R26 = 26,
   UNW_OR1K_R27 = 27,
   UNW_OR1K_R28 = 28,
   UNW_OR1K_R29 = 29,
   UNW_OR1K_R30 = 30,
   UNW_OR1K_R31 = 31,
 };
 
+// MIPS registers
+enum {
+  UNW_MIPS_R0  = 0,
+  UNW_MIPS_R1  = 1,
+  UNW_MIPS_R2  = 2,
+  UNW_MIPS_R3  = 3,
+  UNW_MIPS_R4  = 4,
+  UNW_MIPS_R5  = 5,
+  UNW_MIPS_R6  = 6,
+  UNW_MIPS_R7  = 7,
+  UNW_MIPS_R8  = 8,
+  UNW_MIPS_R9  = 9,
+  UNW_MIPS_R10 = 10,
+  UNW_MIPS_R11 = 11,
+  UNW_MIPS_R12 = 12,
+  UNW_MIPS_R13 = 13,
+  UNW_MIPS_R14 = 14,
+  UNW_MIPS_R15 = 15,
+  UNW_MIPS_R16 = 16,
+  UNW_MIPS_R17 = 17,
+  UNW_MIPS_R18 = 18,
+  UNW_MIPS_R19 = 19,
+  UNW_MIPS_R20 = 20,
+  UNW_MIPS_R21 = 21,
+  UNW_MIPS_R22 = 22,
+  UNW_MIPS_R23 = 23,
+  UNW_MIPS_R24 = 24,
+  UNW_MIPS_R25 = 25,
+  UNW_MIPS_R26 = 26,
+  UNW_MIPS_R27 = 27,
+  UNW_MIPS_R28 = 28,
+  UNW_MIPS_R29 = 29,
+  UNW_MIPS_R30 = 30,
+  UNW_MIPS_R31 = 31,
+  UNW_MIPS_HI = 64,
+  UNW_MIPS_LO = 65,
+};
+
 #endif

src/Registers.hpp

inline const char *Registers_or1k::getRegisterName(int regNum) {
   case UNW_OR1K_R31:
     return "r31";
   default:
     return "unknown register";
   }
 
 }
 #endif // _LIBUNWIND_TARGET_OR1K
+
+#if defined(_LIBUNWIND_TARGET_MIPS_O32)
+/// Registers_mips_o32 holds the register state of a thread in a 32-bit MIPS
+/// process.
+class _LIBUNWIND_HIDDEN Registers_mips_o32 {
+public:
+  Registers_mips_o32();
+  Registers_mips_o32(const void *registers);
+
+  bool        validRegister(int num) const;
+  uint32_t    getRegister(int num) const;
+  void        setRegister(int num, uint32_t value);
+  bool        validFloatRegister(int num) const;
+  double      getFloatRegister(int num) const;
+  void        setFloatRegister(int num, double value);
+  bool        validVectorRegister(int num) const;
+  v128        getVectorRegister(int num) const;
+  void        setVectorRegister(int num, v128 value);
+  const char *getRegisterName(int num);
+  void        jumpto();
+  static int  lastDwarfRegNum() { return _LIBUNWIND_HIGHEST_DWARF_REGISTER_MIPS; }
+
+  uint32_t  getSP() const         { return _registers.__r[29]; }
+  void      setSP(uint32_t value) { _registers.__r[29] = value; }
+  uint32_t  getIP() const         { return _registers.__pc; }
+  void      setIP(uint32_t value) { _registers.__pc = value; }
+
+private:
+  struct mips_o32_thread_state_t {
+    uint32_t __r[32];
+    uint32_t __pc;
+    uint32_t __hi;
+    uint32_t __lo;
+  };
+
+  mips_o32_thread_state_t _registers;
+};
+
+inline Registers_mips_o32::Registers_mips_o32(const void *registers) {
+  static_assert((check_fit<Registers_mips_o32, unw_context_t>::does_fit),
+                "mips_o32 registers do not fit into unw_context_t");
+  memcpy(&_registers, static_cast<const uint8_t *>(registers),
+         sizeof(_registers));
+}
+
+inline Registers_mips_o32::Registers_mips_o32() {
+  memset(&_registers, 0, sizeof(_registers));
+}
+
+inline bool Registers_mips_o32::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 <= UNW_MIPS_R31)
+    return true;
+  if (regNum == UNW_MIPS_HI)
+    return true;
+  if (regNum == UNW_MIPS_LO)
+    return true;
+  // FIXME: Hard float, DSP accumulator registers, MSA registers
+  return false;
+}
+
+inline uint32_t Registers_mips_o32::getRegister(int regNum) const {
+  if (regNum >= UNW_MIPS_R0 && regNum <= UNW_MIPS_R31)
+    return _registers.__r[regNum - UNW_MIPS_R0];
+
+  switch (regNum) {
+  case UNW_REG_IP:
+    return _registers.__pc;
+  case UNW_REG_SP:
+    return _registers.__r[29];
+  case UNW_MIPS_HI:
+    return _registers.__hi;
+  case UNW_MIPS_LO:
+    return _registers.__lo;
+  }
+  _LIBUNWIND_ABORT("unsupported mips_o32 register");
+}
+
+inline void Registers_mips_o32::setRegister(int regNum, uint32_t value) {
+  if (regNum >= UNW_MIPS_R0 && regNum <= UNW_MIPS_R31) {
+    _registers.__r[regNum - UNW_MIPS_R0] = value;
+    return;
+  }
+
+  switch (regNum) {
+  case UNW_REG_IP:
+    _registers.__pc = value;
+    return;
+  case UNW_REG_SP:
+    _registers.__r[29] = value;
+    return;
+  case UNW_MIPS_HI:
+    _registers.__hi = value;
+    return;
+  case UNW_MIPS_LO:
+    _registers.__lo = value;
+    return;
+  }
+  _LIBUNWIND_ABORT("unsupported mips_o32 register");
+}
+
+inline bool Registers_mips_o32::validFloatRegister(int /* regNum */) const {
+  return false;
+}
+
+inline double Registers_mips_o32::getFloatRegister(int /* regNum */) const {
+  _LIBUNWIND_ABORT("mips_o32 float support not implemented");
+}
+
+inline void Registers_mips_o32::setFloatRegister(int /* regNum */,
+                                                 double /* value */) {
+  _LIBUNWIND_ABORT("mips_o32 float support not implemented");
+}
+
+inline bool Registers_mips_o32::validVectorRegister(int /* regNum */) const {
+  return false;
+}
+
+inline v128 Registers_mips_o32::getVectorRegister(int /* regNum */) const {
+  _LIBUNWIND_ABORT("mips_o32 vector support not implemented");
+}
+
+inline void Registers_mips_o32::setVectorRegister(int /* regNum */, v128 /* value */) {
+  _LIBUNWIND_ABORT("mips_o32 vector support not implemented");
+}
+
+inline const char *Registers_mips_o32::getRegisterName(int regNum) {
+  switch (regNum) {
+  case UNW_MIPS_R0:
+    return "$0";
+  case UNW_MIPS_R1:
+    return "$1";
+  case UNW_MIPS_R2:
+    return "$2";
+  case UNW_MIPS_R3:
+    return "$3";
+  case UNW_MIPS_R4:
+    return "$4";
+  case UNW_MIPS_R5:
+    return "$5";
+  case UNW_MIPS_R6:
+    return "$6";
+  case UNW_MIPS_R7:
+    return "$7";
+  case UNW_MIPS_R8:
+    return "$8";
+  case UNW_MIPS_R9:
+    return "$9";
+  case UNW_MIPS_R10:
+    return "$10";
+  case UNW_MIPS_R11:
+    return "$11";
+  case UNW_MIPS_R12:
+    return "$12";
+  case UNW_MIPS_R13:
+    return "$13";
+  case UNW_MIPS_R14:
+    return "$14";
+  case UNW_MIPS_R15:
+    return "$15";
+  case UNW_MIPS_R16:
+    return "$16";
+  case UNW_MIPS_R17:
+    return "$17";
+  case UNW_MIPS_R18:
+    return "$18";
+  case UNW_MIPS_R19:
+    return "$19";
+  case UNW_MIPS_R20:
+    return "$20";
+  case UNW_MIPS_R21:
+    return "$21";
+  case UNW_MIPS_R22:
+    return "$22";
+  case UNW_MIPS_R23:
+    return "$23";
+  case UNW_MIPS_R24:
+    return "$24";
+  case UNW_MIPS_R25:
+    return "$25";
+  case UNW_MIPS_R26:
+    return "$26";
+  case UNW_MIPS_R27:
+    return "$27";
+  case UNW_MIPS_R28:
+    return "$28";
+  case UNW_MIPS_R29:
+    return "$29";
+  case UNW_MIPS_R30:
+    return "$30";
+  case UNW_MIPS_R31:
+    return "$31";
+  case UNW_MIPS_HI:
+    return "$hi";
+  case UNW_MIPS_LO:
+    return "$lo";
+  default:
+    return "unknown register";
+  }
+}
+#endif // _LIBUNWIND_TARGET_MIPS_O32
+
+#if defined(_LIBUNWIND_TARGET_MIPS_N64)
+/// Registers_mips_n64 holds the register state of a thread in a 64-bit MIPS
+/// process.
+class _LIBUNWIND_HIDDEN Registers_mips_n64 {
+public:
+  Registers_mips_n64();
+  Registers_mips_n64(const void *registers);
+
+  bool        validRegister(int num) const;
+  uint64_t    getRegister(int num) const;
+  void        setRegister(int num, uint64_t value);
+  bool        validFloatRegister(int num) const;
+  double      getFloatRegister(int num) const;
+  void        setFloatRegister(int num, double value);
+  bool        validVectorRegister(int num) const;
+  v128        getVectorRegister(int num) const;
+  void        setVectorRegister(int num, v128 value);
+  const char *getRegisterName(int num);
+  void        jumpto();
+  static int  lastDwarfRegNum() { return _LIBUNWIND_HIGHEST_DWARF_REGISTER_MIPS; }
+
+  uint64_t  getSP() const         { return _registers.__r[29]; }
+  void      setSP(uint64_t value) { _registers.__r[29] = value; }
+  uint64_t  getIP() const         { return _registers.__pc; }
+  void      setIP(uint64_t value) { _registers.__pc = value; }
+
+private:
+  struct mips_n64_thread_state_t {
+    uint64_t __r[32];
+    uint64_t __pc;
+    uint64_t __hi;
+    uint64_t __lo;
+  };
+
+  mips_n64_thread_state_t _registers;
+};
+
+inline Registers_mips_n64::Registers_mips_n64(const void *registers) {
+  static_assert((check_fit<Registers_mips_n64, unw_context_t>::does_fit),
+                "mips_n64 registers do not fit into unw_context_t");
+  memcpy(&_registers, static_cast<const uint8_t *>(registers),
+         sizeof(_registers));
+}
+
+inline Registers_mips_n64::Registers_mips_n64() {
+  memset(&_registers, 0, sizeof(_registers));
+}
+
+inline bool Registers_mips_n64::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 <= UNW_MIPS_R31)
+    return true;
+  if (regNum == UNW_MIPS_HI)
+    return true;
+  if (regNum == UNW_MIPS_LO)
+    return true;
+  // FIXME: Hard float, DSP accumulator registers, MSA registers
+  return false;
+}
+
+inline uint64_t Registers_mips_n64::getRegister(int regNum) const {
+  if (regNum >= UNW_MIPS_R0 && regNum <= UNW_MIPS_R31)
+    return _registers.__r[regNum - UNW_MIPS_R0];
+
+  switch (regNum) {
+  case UNW_REG_IP:
+    return _registers.__pc;
+  case UNW_REG_SP:
+    return _registers.__r[29];
+  case UNW_MIPS_HI:
+    return _registers.__hi;
+  case UNW_MIPS_LO:
+    return _registers.__lo;
+  }
+  _LIBUNWIND_ABORT("unsupported mips_n64 register");
+}
+
+inline void Registers_mips_n64::setRegister(int regNum, uint64_t value) {
+  if (regNum >= UNW_MIPS_R0 && regNum <= UNW_MIPS_R31) {
+    _registers.__r[regNum - UNW_MIPS_R0] = value;
+    return;
+  }
+
+  switch (regNum) {
+  case UNW_REG_IP:
+    _registers.__pc = value;
+    return;
+  case UNW_REG_SP:
+    _registers.__r[29] = value;
+    return;
+  case UNW_MIPS_HI:
+    _registers.__hi = value;
+    return;
+  case UNW_MIPS_LO:
+    _registers.__lo = value;
+    return;
+  }
+  _LIBUNWIND_ABORT("unsupported mips_n64 register");
+}
+
+inline bool Registers_mips_n64::validFloatRegister(int /* regNum */) const {
+  return false;
+}
+
+inline double Registers_mips_n64::getFloatRegister(int /* regNum */) const {
+  _LIBUNWIND_ABORT("mips_n64 float support not implemented");
+}
+
+inline void Registers_mips_n64::setFloatRegister(int /* regNum */,
+                                                 double /* value */) {
+  _LIBUNWIND_ABORT("mips_n64 float support not implemented");
+}
+
+inline bool Registers_mips_n64::validVectorRegister(int /* regNum */) const {
+  return false;
+}
+
+inline v128 Registers_mips_n64::getVectorRegister(int /* regNum */) const {
+  _LIBUNWIND_ABORT("mips_n64 vector support not implemented");
+}
+
+inline void Registers_mips_n64::setVectorRegister(int /* regNum */, v128 /* value */) {
+  _LIBUNWIND_ABORT("mips_n64 vector support not implemented");
+}
+
+inline const char *Registers_mips_n64::getRegisterName(int regNum) {
+  switch (regNum) {
+  case UNW_MIPS_R0:
+    return "$0";
+  case UNW_MIPS_R1:
+    return "$1";
+  case UNW_MIPS_R2:
+    return "$2";
+  case UNW_MIPS_R3:
+    return "$3";
+  case UNW_MIPS_R4:
+    return "$4";
+  case UNW_MIPS_R5:
+    return "$5";
+  case UNW_MIPS_R6:
+    return "$6";
+  case UNW_MIPS_R7:
+    return "$7";
+  case UNW_MIPS_R8:
+    return "$8";
+  case UNW_MIPS_R9:
+    return "$9";
+  case UNW_MIPS_R10:
+    return "$10";
+  case UNW_MIPS_R11:
+    return "$11";
+  case UNW_MIPS_R12:
+    return "$12";
+  case UNW_MIPS_R13:
+    return "$13";
+  case UNW_MIPS_R14:
+    return "$14";
+  case UNW_MIPS_R15:
+    return "$15";
+  case UNW_MIPS_R16:
+    return "$16";
+  case UNW_MIPS_R17:
+    return "$17";
+  case UNW_MIPS_R18:
+    return "$18";
+  case UNW_MIPS_R19:
+    return "$19";
+  case UNW_MIPS_R20:
+    return "$20";
+  case UNW_MIPS_R21:
+    return "$21";
+  case UNW_MIPS_R22:
+    return "$22";
+  case UNW_MIPS_R23:
+    return "$23";
+  case UNW_MIPS_R24:
+    return "$24";
+  case UNW_MIPS_R25:
+    return "$25";
+  case UNW_MIPS_R26:
+    return "$26";
+  case UNW_MIPS_R27:
+    return "$27";
+  case UNW_MIPS_R28:
+    return "$28";
+  case UNW_MIPS_R29:
+    return "$29";
+  case UNW_MIPS_R30:
+    return "$30";
+  case UNW_MIPS_R31:
+    return "$31";
+  case UNW_MIPS_HI:
+    return "$hi";
+  case UNW_MIPS_LO:
+    return "$lo";
+  default:
+    return "unknown register";
+  }
+}
+#endif // _LIBUNWIND_TARGET_MIPS_N64
 } // namespace libunwind
 
 #endif // __REGISTERS_HPP__

src/UnwindCursor.hpp

 
 #if defined(_LIBUNWIND_TARGET_AARCH64)
   int stepWithCompactEncoding(Registers_arm64 &) {
     return CompactUnwinder_arm64<A>::stepWithCompactEncoding(
         _info.format, _info.start_ip, _addressSpace, _registers);
   }
 #endif
 
+#if defined(_LIBUNWIND_TARGET_MIPS_O32)
+  int stepWithCompactEncoding(Registers_mips_o32 &) {
+    return UNW_EINVAL;
+  }
+#endif
+
+#if defined(_LIBUNWIND_TARGET_MIPS_N64)
+  int stepWithCompactEncoding(Registers_mips_n64 &) {
+    return UNW_EINVAL;
+  }
+#endif
+
   bool compactSaysUseDwarf(uint32_t *offset=NULL) const {
     R dummy;
     return compactSaysUseDwarf(dummy, offset);
   }
 
 #if defined(_LIBUNWIND_TARGET_X86_64)
   bool compactSaysUseDwarf(Registers_x86_64 &, uint32_t *offset) const {
     if ((_info.format & UNWIND_X86_64_MODE_MASK) == UNWIND_X86_64_MODE_DWARF) {
bool compactSaysUseDwarf(Registers_arm64 &, uint32_t *offset) const {
     if ((_info.format & UNWIND_ARM64_MODE_MASK) == UNWIND_ARM64_MODE_DWARF) {
       if (offset)
         *offset = (_info.format & UNWIND_ARM64_DWARF_SECTION_OFFSET);
       return true;
     }
     return false;
   }
 #endif
+
+#if defined(_LIBUNWIND_TARGET_MIPS_O32)
+  bool compactSaysUseDwarf(Registers_mips_o32 &, uint32_t *) const {
+    return true;
+  }
+#endif
+
+#if defined(_LIBUNWIND_TARGET_MIPS_N64)
+  bool compactSaysUseDwarf(Registers_mips_n64 &, uint32_t *) const {
+    return true;
+  }
+#endif
 #endif // defined(_LIBUNWIND_SUPPORT_COMPACT_UNWIND)
 
 #if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
   compact_unwind_encoding_t dwarfEncoding() const {
     R dummy;
     return dwarfEncoding(dummy);
   }
 
#if defined(_LIBUNWIND_TARGET_AARCH64)
   }
 #endif
 
 #if defined (_LIBUNWIND_TARGET_OR1K)
   compact_unwind_encoding_t dwarfEncoding(Registers_or1k &) const {
     return 0;
   }
 #endif
+
+#if defined (_LIBUNWIND_TARGET_MIPS_O32)
+  compact_unwind_encoding_t dwarfEncoding(Registers_mips_o32 &) const {
+    return 0;
+  }
+#endif
+
+#if defined (_LIBUNWIND_TARGET_MIPS_N64)
+  compact_unwind_encoding_t dwarfEncoding(Registers_mips_n64 &) const {
+    return 0;
+  }
+#endif
 #endif // defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
 
 
   A               &_addressSpace;
   R                _registers;
   unw_proc_info_t  _info;
   bool             _unwindInfoMissing;
   bool             _isSignalFrame;

src/UnwindRegistersRestore.S

#
 
   # at last, restore r3
   l.lwz    r3,  12(r3)
 
   # jump to pc
   l.jr     r9
    l.nop
 
+#elif defined(__mips__) && defined(_ABIO32) && defined(__mips_soft_float)
+
+//
+// void libunwind::Registers_mips_o32::jumpto()
+//
+// On entry:
+//  thread state pointer is in a0 ($4)
+//
+DEFINE_LIBUNWIND_PRIVATE_FUNCTION(_ZN9libunwind18Registers_mips_o326jumptoEv)
+  .set push
+  .set noat
+  .set noreorder
+  .set nomacro
+  // restore hi and lo
+  lw    $8, (4 * 33)($4)
+  mthi  $8
+  lw    $8, (4 * 34)($4)
+  mtlo  $8
+  // r0 is zero
+  lw    $1, (4 * 1)($4)
+  lw    $2, (4 * 2)($4)
+  lw    $3, (4 * 3)($4)
+  // skip a0 for now
+  lw    $5, (4 * 5)($4)
+  lw    $6, (4 * 6)($4)
+  lw    $7, (4 * 7)($4)
+  lw    $8, (4 * 8)($4)
+  lw    $9, (4 * 9)($4)
+  lw    $10, (4 * 10)($4)
+  lw    $11, (4 * 11)($4)
+  lw    $12, (4 * 12)($4)
+  lw    $13, (4 * 13)($4)
+  lw    $14, (4 * 14)($4)
+  lw    $15, (4 * 15)($4)
+  lw    $16, (4 * 16)($4)
+  lw    $17, (4 * 17)($4)
+  lw    $18, (4 * 18)($4)
+  lw    $19, (4 * 19)($4)
+  lw    $20, (4 * 20)($4)
+  lw    $21, (4 * 21)($4)
+  lw    $22, (4 * 22)($4)
+  lw    $23, (4 * 23)($4)
+  lw    $24, (4 * 24)($4)
+  lw    $25, (4 * 25)($4)
+  lw    $26, (4 * 26)($4)
+  lw    $27, (4 * 27)($4)
+  lw    $28, (4 * 28)($4)
+  lw    $29, (4 * 29)($4)
+  lw    $30, (4 * 30)($4)
+  // load new pc into ra
+  lw    $31, (4 * 32)($4)
+  // jump to ra, load a0 in the delay slot
+  jr    $31
+  lw    $4, (4 * 4)($4)
+  .set pop
+
+#elif defined(__mips__) && defined(_ABI64) && defined(__mips_soft_float)
+
+//
+// void libunwind::Registers_mips_n64::jumpto()
+//
+// On entry:
+//  thread state pointer is in a0 ($4)
+//
+DEFINE_LIBUNWIND_PRIVATE_FUNCTION(_ZN9libunwind18Registers_mips_n646jumptoEv)
+  .set push
+  .set noat
+  .set noreorder
+  .set nomacro
+  // restore hi and lo
+  ld    $8, (8 * 33)($4)
+  mthi  $8
+  ld    $8, (8 * 34)($4)
+  mtlo  $8
+  // r0 is zero
+  ld    $1, (8 * 1)($4)
+  ld    $2, (8 * 2)($4)
+  ld    $3, (8 * 3)($4)
+  // skip a0 for now
+  ld    $5, (8 * 5)($4)
+  ld    $6, (8 * 6)($4)
+  ld    $7, (8 * 7)($4)
+  ld    $8, (8 * 8)($4)
+  ld    $9, (8 * 9)($4)
+  ld    $10, (8 * 10)($4)
+  ld    $11, (8 * 11)($4)
+  ld    $12, (8 * 12)($4)
+  ld    $13, (8 * 13)($4)
+  ld    $14, (8 * 14)($4)
+  ld    $15, (8 * 15)($4)
+  ld    $16, (8 * 16)($4)
+  ld    $17, (8 * 17)($4)
+  ld    $18, (8 * 18)($4)
+  ld    $19, (8 * 19)($4)
+  ld    $20, (8 * 20)($4)
+  ld    $21, (8 * 21)($4)
+  ld    $22, (8 * 22)($4)
+  ld    $23, (8 * 23)($4)
+  ld    $24, (8 * 24)($4)
+  ld    $25, (8 * 25)($4)
+  ld    $26, (8 * 26)($4)
+  ld    $27, (8 * 27)($4)
+  ld    $28, (8 * 28)($4)
+  ld    $29, (8 * 29)($4)
+  ld    $30, (8 * 30)($4)
+  // load new pc into ra
+  ld    $31, (8 * 32)($4)
+  // jump to ra, load a0 in the delay slot
+  jr    $31
+  ld    $4, (8 * 4)($4)
+  .set pop
+
 #endif
 
 #endif /* !defined(__USING_SJLJ_EXCEPTIONS__) */
 
 NO_EXEC_STACK_DIRECTIVE
 

src/UnwindRegistersSave.S

#if defined(_WIN64)
   movdqu %xmm12,368(PTR)
   movdqu %xmm13,384(PTR)
   movdqu %xmm14,400(PTR)
   movdqu %xmm15,416(PTR)
 #endif
   xorl  %eax, %eax    # return UNW_ESUCCESS
   ret
 
+#elif defined(__mips__) && defined(_ABIO32) && defined(__mips_soft_float)
+
+#
+# extern int unw_getcontext(unw_context_t* thread_state)
+#
+# On entry:
+#  thread_state pointer is in a0 ($4)
+#
+DEFINE_LIBUNWIND_FUNCTION(unw_getcontext)
+  .set push
+  .set noat
+  .set noreorder
+  .set nomacro
+  sw    $1, (4 * 1)($4)
+  sw    $2, (4 * 2)($4)
+  sw    $3, (4 * 3)($4)
+  sw    $4, (4 * 4)($4)
+  sw    $5, (4 * 5)($4)
+  sw    $6, (4 * 6)($4)
+  sw    $7, (4 * 7)($4)
+  sw    $8, (4 * 8)($4)
+  sw    $9, (4 * 9)($4)
+  sw    $10, (4 * 10)($4)
+  sw    $11, (4 * 11)($4)
+  sw    $12, (4 * 12)($4)
+  sw    $13, (4 * 13)($4)
+  sw    $14, (4 * 14)($4)
+  sw    $15, (4 * 15)($4)
+  sw    $16, (4 * 16)($4)
+  sw    $17, (4 * 17)($4)
+  sw    $18, (4 * 18)($4)
+  sw    $19, (4 * 19)($4)
+  sw    $20, (4 * 20)($4)
+  sw    $21, (4 * 21)($4)
+  sw    $22, (4 * 22)($4)
+  sw    $23, (4 * 23)($4)
+  sw    $24, (4 * 24)($4)
+  sw    $25, (4 * 25)($4)
+  sw    $26, (4 * 26)($4)
+  sw    $27, (4 * 27)($4)
+  sw    $28, (4 * 28)($4)
+  sw    $29, (4 * 29)($4)
+  sw    $30, (4 * 30)($4)
+  sw    $31, (4 * 31)($4)
+  # Store return address to pc
+  sw    $31, (4 * 32)($4)
+  # hi and lo
+  mfhi  $8
+  sw    $8,  (4 * 33)($4)
+  mflo  $8
+  sw    $8,  (4 * 34)($4)
+  jr  $31
+  # return UNW_ESUCCESS
+  or    $2, $0, $0
+  .set pop
+
+#elif defined(__mips__) && defined(_ABI64) && defined(__mips_soft_float)
+
+#
+# extern int unw_getcontext(unw_context_t* thread_state)
+#
+# On entry:
+#  thread_state pointer is in a0 ($4)
+#
+DEFINE_LIBUNWIND_FUNCTION(unw_getcontext)
+  .set push
+  .set noat
+  .set noreorder
+  .set nomacro
+  sd    $1, (8 * 1)($4)
+  sd    $2, (8 * 2)($4)
+  sd    $3, (8 * 3)($4)
+  sd    $4, (8 * 4)($4)
+  sd    $5, (8 * 5)($4)
+  sd    $6, (8 * 6)($4)
+  sd    $7, (8 * 7)($4)
+  sd    $8, (8 * 8)($4)
+  sd    $9, (8 * 9)($4)
+  sd    $10, (8 * 10)($4)
+  sd    $11, (8 * 11)($4)
+  sd    $12, (8 * 12)($4)
+  sd    $13, (8 * 13)($4)
+  sd    $14, (8 * 14)($4)
+  sd    $15, (8 * 15)($4)
+  sd    $16, (8 * 16)($4)
+  sd    $17, (8 * 17)($4)
+  sd    $18, (8 * 18)($4)
+  sd    $19, (8 * 19)($4)
+  sd    $20, (8 * 20)($4)
+  sd    $21, (8 * 21)($4)
+  sd    $22, (8 * 22)($4)
+  sd    $23, (8 * 23)($4)
+  sd    $24, (8 * 24)($4)
+  sd    $25, (8 * 25)($4)
+  sd    $26, (8 * 26)($4)
+  sd    $27, (8 * 27)($4)
+  sd    $28, (8 * 28)($4)
+  sd    $29, (8 * 29)($4)
+  sd    $30, (8 * 30)($4)
+  sd    $31, (8 * 31)($4)
+  # Store return address to pc
+  sd    $31, (8 * 32)($4)
+  # hi and lo
+  mfhi  $8
+  sd    $8,  (8 * 33)($4)
+  mflo  $8
+  sd    $8,  (8 * 34)($4)
+  jr  $31
+  # return UNW_ESUCCESS
+  or    $2, $0, $0
+  .set pop
+
 # elif defined(__mips__)
 
 #
 # extern int unw_getcontext(unw_context_t* thread_state)
 #
 # Just trap for the time being.
 DEFINE_LIBUNWIND_FUNCTION(unw_getcontext)
   teq $0, $0

src/config.h

 #if defined(__i386__) || defined(__x86_64__) || defined(__ppc__) || defined(__ppc64__)
 #define _LIBUNWIND_SUPPORT_FRAME_APIS
 #endif
 
 #if defined(__i386__) || defined(__x86_64__) ||                                \
     defined(__ppc__) || defined(__ppc64__) ||                                  \
     (!defined(__APPLE__) && defined(__arm__)) ||                               \
     (defined(__arm64__) || defined(__aarch64__)) ||                            \
-    (defined(__APPLE__) && defined(__mips__))
+    defined(__mips__)
 #define _LIBUNWIND_BUILD_ZERO_COST_APIS
 #endif
 
 #if defined(NDEBUG) && defined(_LIBUNWIND_IS_BAREMETAL)
 #define _LIBUNWIND_ABORT(msg)                                                  \
   do {                                                                         \
     abort();                                                                   \
   } while (0)

src/libunwind.cpp

 #elif defined(__ppc__)
 # define REGISTER_KIND Registers_ppc
 #elif defined(__aarch64__)
 # define REGISTER_KIND Registers_arm64
 #elif defined(_LIBUNWIND_ARM_EHABI)
 # define REGISTER_KIND Registers_arm
 #elif defined(__or1k__)
 # define REGISTER_KIND Registers_or1k
+#elif defined(__mips__) && defined(_ABIO32) && defined(__mips_soft_float)
+# define REGISTER_KIND Registers_mips_o32
+#elif defined(__mips__) && defined(_ABI64) && defined(__mips_soft_float)
+# define REGISTER_KIND Registers_mips_n64
 #elif defined(__mips__)
-# warning The MIPS architecture is not supported.
+# warning The MIPS architecture is not supported with this ABI and environment!
 #else
 # error Architecture not supported
 #endif
   // Use "placement new" to allocate UnwindCursor in the cursor buffer.
   new ((void *)cursor) UnwindCursor<LocalAddressSpace, REGISTER_KIND>(
                                  context, LocalAddressSpace::sThisAddressSpace);
 #undef REGISTER_KIND
   AbstractUnwindCursor *co = (AbstractUnwindCursor *)cursor;