[libunwind] Convert x86, x86_64, arm64 register restore functions to …

…C calling convention and name mangling

Currently, the assembly functions for restoring register state have
been direct implementations of the Registers_*::jumpto() method
(contrary to the functions for saving register state, which are
implementations of the extern C function __unw_getcontext). This has
included having the assembly function name match the C++ mangling of
that method name (and having the function match the C++ member
function calling convention). To simplify the interface of the assembly
implementations, make the functions have C calling conventions and
name mangling.

This fixes building the library in with a MSVC C++ ABI with clang-cl,
which uses a significantly different method name mangling scheme.
(The library might not be of much use as C++ exception unwinder in such
an environment, but the libunwind.h interface for stepwise unwinding
still is usable, as is the _Unwind_Backtrace function.)

Differential Revision: https://reviews.llvm.org/D86041

libunwind/src/Registers.hpp

@@ -39,6 +39,8 @@ enum {
 };
 
 #if defined(_LIBUNWIND_TARGET_I386)
+class _LIBUNWIND_HIDDEN Registers_x86;
+extern "C" void __libunwind_Registers_x86_jumpto(Registers_x86 *);
 /// Registers_x86 holds the register state of a thread in a 32-bit intel
 /// process.
 class _LIBUNWIND_HIDDEN Registers_x86 {
@@ -56,7 +58,7 @@ class _LIBUNWIND_HIDDEN Registers_x86 {
   v128        getVectorRegister(int num) const;
   void        setVectorRegister(int num, v128 value);
   static const char *getRegisterName(int num);
-  void        jumpto();
+  void        jumpto() { __libunwind_Registers_x86_jumpto(this); }
   static int  lastDwarfRegNum() { return _LIBUNWIND_HIGHEST_DWARF_REGISTER_X86; }
   static int  getArch() { return REGISTERS_X86; }
 
@@ -248,6 +250,8 @@ inline void Registers_x86::setVectorRegister(int, v128) {
 #if defined(_LIBUNWIND_TARGET_X86_64)
 /// Registers_x86_64  holds the register state of a thread in a 64-bit intel
 /// process.
+class _LIBUNWIND_HIDDEN Registers_x86_64;
+extern "C" void __libunwind_Registers_x86_64_jumpto(Registers_x86_64 *);
 class _LIBUNWIND_HIDDEN Registers_x86_64 {
 public:
   Registers_x86_64();
@@ -263,7 +267,7 @@ class _LIBUNWIND_HIDDEN Registers_x86_64 {
   v128        getVectorRegister(int num) const;
   void        setVectorRegister(int num, v128 value);
   static const char *getRegisterName(int num);
-  void        jumpto();
+  void        jumpto() { __libunwind_Registers_x86_64_jumpto(this); }
   static int  lastDwarfRegNum() { return _LIBUNWIND_HIGHEST_DWARF_REGISTER_X86_64; }
   static int  getArch() { return REGISTERS_X86_64; }
 
@@ -1771,6 +1775,8 @@ inline const char *Registers_ppc64::getRegisterName(int regNum) {
 #if defined(_LIBUNWIND_TARGET_AARCH64)
 /// Registers_arm64  holds the register state of a thread in a 64-bit arm
 /// process.
+class _LIBUNWIND_HIDDEN Registers_arm64;
+extern "C" void __libunwind_Registers_arm64_jumpto(Registers_arm64 *);
 class _LIBUNWIND_HIDDEN Registers_arm64 {
 public:
   Registers_arm64();
@@ -1786,7 +1792,7 @@ class _LIBUNWIND_HIDDEN Registers_arm64 {
   v128        getVectorRegister(int num) const;
   void        setVectorRegister(int num, v128 value);
   static const char *getRegisterName(int num);
-  void        jumpto();
+  void        jumpto() { __libunwind_Registers_arm64_jumpto(this); }
   static int  lastDwarfRegNum() { return _LIBUNWIND_HIGHEST_DWARF_REGISTER_ARM64; }
   static int  getArch() { return REGISTERS_ARM64; }
 

libunwind/src/UnwindRegistersRestore.S

@@ -13,14 +13,10 @@
 #if !defined(__USING_SJLJ_EXCEPTIONS__)
 
 #if defined(__i386__)
-DEFINE_LIBUNWIND_FUNCTION(_ZN9libunwind13Registers_x866jumptoEv)
+DEFINE_LIBUNWIND_FUNCTION(__libunwind_Registers_x86_jumpto)
 #
-# void libunwind::Registers_x86::jumpto()
+# extern "C" void __libunwind_Registers_x86_jumpto(Registers_x86 *);
 #
-#if defined(_WIN32)
-# On windows, the 'this' pointer is passed in ecx instead of on the stack
-  movl   %ecx, %eax
-#else
 # On entry:
 #  +                       +
 #  +-----------------------+
@@ -30,7 +26,6 @@ DEFINE_LIBUNWIND_FUNCTION(_ZN9libunwind13Registers_x866jumptoEv)
 #  +-----------------------+   <-- SP
 #  +                       +
   movl   4(%esp), %eax
-#endif
   # set up eax and ret on new stack location
   movl  28(%eax), %edx # edx holds new stack pointer
   subl  $8,%edx
@@ -60,9 +55,9 @@ DEFINE_LIBUNWIND_FUNCTION(_ZN9libunwind13Registers_x866jumptoEv)
 
 #elif defined(__x86_64__)
 
-DEFINE_LIBUNWIND_FUNCTION(_ZN9libunwind16Registers_x86_646jumptoEv)
+DEFINE_LIBUNWIND_FUNCTION(__libunwind_Registers_x86_64_jumpto)
 #
-# void libunwind::Registers_x86_64::jumpto()
+# extern "C" void __libunwind_Registers_x86_64_jumpto(Registers_x86_64 *);
 #
 #if defined(_WIN64)
 # On entry, thread_state pointer is in rcx; move it into rdi
@@ -560,13 +555,13 @@ Lnovec:
 #elif defined(__aarch64__)
 
 //
-// void libunwind::Registers_arm64::jumpto()
+// extern "C" void __libunwind_Registers_arm64_jumpto(Registers_arm64 *);
 //
 // On entry:
 //  thread_state pointer is in x0
 //
   .p2align 2
-DEFINE_LIBUNWIND_FUNCTION(_ZN9libunwind15Registers_arm646jumptoEv)
+DEFINE_LIBUNWIND_FUNCTION(__libunwind_Registers_arm64_jumpto)
   // skip restore of x0,x1 for now
   ldp    x2, x3,  [x0, #0x010]
   ldp    x4, x5,  [x0, #0x020]