/*++
Function:
PAL_VirtualUnwindOutOfProc
Unwind the stack given the context for a "remote" target using the
provided read memory callback.
Assumes the IP is in the module of the base address provided (coreclr).
Parameters:
context - the start context in the target
contextPointers - the context of the next frame
baseAddress - base address of the module to find the unwind info
readMemoryCallback - reads memory from the target
--*/
BOOL
PALAPI
PAL_VirtualUnwindOutOfProc(CONTEXT *context, KNONVOLATILE_CONTEXT_POINTERS *contextPointers, SIZE_T baseAddress, UnwindReadMemoryCallback readMemoryCallback)
{
unw_addr_space_t addrSpace = 0;
unw_cursor_t cursor;
libunwindInfo info;
BOOL result = FALSE;
int st;
info.BaseAddress = baseAddress;
info.Context = context;
info.ReadMemory = readMemoryCallback;
addrSpace = unw_create_addr_space(&unwind_accessors, 0);
st = unw_init_remote(&cursor, addrSpace, &info);
if (st < 0)
{
result = FALSE;
goto exit;
}
st = unw_step(&cursor);
if (st < 0)
{
result = FALSE;
goto exit;
}
UnwindContextToWinContext(&cursor, context);
if (contextPointers != NULL)
{
GetContextPointers(&cursor, NULL, contextPointers);
}
result = TRUE;
exit:
if (addrSpace != 0)
{
unw_destroy_addr_space(addrSpace);
}
return result;
}
BOOL PAL_VirtualUnwindOutOfProc(CONTEXT *context,
KNONVOLATILE_CONTEXT_POINTERS *contextPointers,
DWORD pid,
ReadMemoryWordCallback readMemCallback)
{
// This function can be executed only by one thread at a time.
// The reason for this is that we need to pass context and read mem function to libunwind callbacks
// but "arg" is already used by the pointer returned from _UPT_create().
// So we resort to using global variables and a lock.
struct Lock
{
CRITICAL_SECTION cs;
Lock()
{
// ctor of a static variable is a thread-safe way to initialize critical section exactly once (clang,gcc)
InitializeCriticalSection(&cs);
}
};
struct LockHolder
{
CRITICAL_SECTION *cs;
LockHolder(CRITICAL_SECTION *cs)
{
this->cs = cs;
EnterCriticalSection(cs);
}
~LockHolder()
{
LeaveCriticalSection(cs);
cs = NULL;
}
};
static Lock lock;
LockHolder lockHolder(&lock.cs);
int st;
unw_context_t unwContext;
unw_cursor_t cursor;
unw_addr_space_t addrSpace = 0;
void *libunwindUptPtr = NULL;
BOOL result = FALSE;
LibunwindCallbacksInfo.Context = context;
LibunwindCallbacksInfo.readMemCallback = readMemCallback;
WinContextToUnwindContext(context, &unwContext);
addrSpace = unw_create_addr_space(&unwind_accessors, 0);
libunwindUptPtr = _UPT_create(pid);
st = unw_init_remote(&cursor, addrSpace, libunwindUptPtr);
if (st < 0)
{
result = FALSE;
goto Exit;
}
st = unw_step(&cursor);
if (st < 0)
{
result = FALSE;
goto Exit;
}
UnwindContextToWinContext(&cursor, context);
if (contextPointers != NULL)
{
GetContextPointers(&cursor, &unwContext, contextPointers);
}
result = TRUE;
Exit:
if (libunwindUptPtr != nullptr)
{
_UPT_destroy(libunwindUptPtr);
}
if (addrSpace != 0)
{
unw_destroy_addr_space(addrSpace);
}
return result;
}
BOOL PAL_VirtualUnwind(CONTEXT *context, KNONVOLATILE_CONTEXT_POINTERS *contextPointers)
{
int st;
unw_context_t unwContext;
unw_cursor_t cursor;
#if defined(__APPLE__) || defined(__FreeBSD__) || defined(_ARM64_)
DWORD64 curPc;
#endif
if ((context->ContextFlags & CONTEXT_EXCEPTION_ACTIVE) != 0)
{
// The current frame is a source of hardware exception. Due to the fact that
// we use the low level unwinder to unwind just one frame a time, the
// unwinder doesn't have the signal_frame flag set. So it doesn't
// know that it should not decrement the PC before looking up the unwind info.
// So we compensate it by incrementing the PC before passing it to the unwinder.
// Without it, the unwinder would not find unwind info if the hardware exception
// happened in the first instruction of a function.
SetPc(context, GetPc(context) + 1);
}
#if UNWIND_CONTEXT_IS_UCONTEXT_T
WinContextToUnwindContext(context, &unwContext);
#else
st = unw_getcontext(&unwContext);
if (st < 0)
{
return FALSE;
}
#endif
st = unw_init_local(&cursor, &unwContext);
if (st < 0)
{
return FALSE;
}
#if !UNWIND_CONTEXT_IS_UCONTEXT_T
// Set the unwind context to the specified windows context
WinContextToUnwindCursor(context, &cursor);
#endif
#if defined(__APPLE__) || defined(__FreeBSD__) || defined(_ARM64_)
// OSX and FreeBSD appear to do two different things when unwinding
// 1: If it reaches where it cannot unwind anymore, say a
// managed frame. It wil return 0, but also update the $pc
// 2: If it unwinds all the way to _start it will return
// 0 from the step, but $pc will stay the same.
// The behaviour of libunwind from nongnu.org is to null the PC
// So we bank the original PC here, so we can compare it after
// the step
curPc = GetPc(context);
#endif
st = unw_step(&cursor);
if (st < 0)
{
return FALSE;
}
// Check if the frame we have unwound to is a frame that caused
// synchronous signal, like a hardware exception and record it
// in the context flags.
st = unw_is_signal_frame(&cursor);
if (st > 0)
{
context->ContextFlags |= CONTEXT_EXCEPTION_ACTIVE;
}
else
{
context->ContextFlags &= ~CONTEXT_EXCEPTION_ACTIVE;
}
// Update the passed in windows context to reflect the unwind
//
UnwindContextToWinContext(&cursor, context);
#if defined(__APPLE__) || defined(__FreeBSD__) || defined(_ARM64_)
if (st == 0 && GetPc(context) == curPc)
{
SetPc(context, 0);
}
#endif
if (contextPointers != NULL)
{
GetContextPointers(&cursor, &unwContext, contextPointers);
}
return TRUE;
}
BOOL PAL_VirtualUnwind(CONTEXT *context, KNONVOLATILE_CONTEXT_POINTERS *contextPointers)
{
int st;
unw_context_t unwContext;
unw_cursor_t cursor;
DWORD64 curPc = CONTEXTGetPC(context);
#ifndef __APPLE__
// Check if the PC is the return address from the SEHProcessException in the common_signal_handler.
// If that's the case, extract its local variable containing the windows style context of the hardware
// exception and return that. This skips the hardware signal handler trampoline that the libunwind
// cannot cross on some systems.
if ((void*)curPc == g_SEHProcessExceptionReturnAddress)
{
CONTEXT* signalContext = (CONTEXT*)(CONTEXTGetFP(context) + g_common_signal_handler_context_locvar_offset);
memcpy_s(context, sizeof(CONTEXT), signalContext, sizeof(CONTEXT));
return TRUE;
}
#endif
if ((context->ContextFlags & CONTEXT_EXCEPTION_ACTIVE) != 0)
{
// The current frame is a source of hardware exception. Due to the fact that
// we use the low level unwinder to unwind just one frame a time, the
// unwinder doesn't have the signal_frame flag set. So it doesn't
// know that it should not decrement the PC before looking up the unwind info.
// So we compensate it by incrementing the PC before passing it to the unwinder.
// Without it, the unwinder would not find unwind info if the hardware exception
// happened in the first instruction of a function.
CONTEXTSetPC(context, curPc + 1);
}
#if !UNWIND_CONTEXT_IS_UCONTEXT_T
st = unw_getcontext(&unwContext);
if (st < 0)
{
return FALSE;
}
#endif
WinContextToUnwindContext(context, &unwContext);
st = unw_init_local(&cursor, &unwContext);
if (st < 0)
{
return FALSE;
}
#if !UNWIND_CONTEXT_IS_UCONTEXT_T
// Set the unwind context to the specified windows context
WinContextToUnwindCursor(context, &cursor);
#endif
st = unw_step(&cursor);
if (st < 0)
{
return FALSE;
}
// Check if the frame we have unwound to is a frame that caused
// synchronous signal, like a hardware exception and record it
// in the context flags.
if (unw_is_signal_frame(&cursor) > 0)
{
context->ContextFlags |= CONTEXT_EXCEPTION_ACTIVE;
#if defined(_ARM_) || defined(_ARM64_) || defined(_X86_)
context->ContextFlags &= ~CONTEXT_UNWOUND_TO_CALL;
#endif // _ARM_ || _ARM64_
}
else
{
context->ContextFlags &= ~CONTEXT_EXCEPTION_ACTIVE;
#if defined(_ARM_) || defined(_ARM64_) || defined(_X86_)
context->ContextFlags |= CONTEXT_UNWOUND_TO_CALL;
#endif // _ARM_ || _ARM64_
}
// Update the passed in windows context to reflect the unwind
//
UnwindContextToWinContext(&cursor, context);
// FreeBSD, NetBSD, OSX and Alpine appear to do two different things when unwinding
// 1: If it reaches where it cannot unwind anymore, say a
// managed frame. It will return 0, but also update the $pc
// 2: If it unwinds all the way to _start it will return
// 0 from the step, but $pc will stay the same.
// So we detect that here and set the $pc to NULL in that case.
// This is the default behavior of the libunwind on Linux.
if (st == 0 && CONTEXTGetPC(context) == curPc)
{
CONTEXTSetPC(context, 0);
}
if (contextPointers != NULL)
{
GetContextPointers(&cursor, &unwContext, contextPointers);
}
return TRUE;
}
BOOL PAL_VirtualUnwind(CONTEXT *context, KNONVOLATILE_CONTEXT_POINTERS *contextPointers)
{
int st;
unw_context_t unwContext;
unw_cursor_t cursor;
#if defined(__APPLE__) || defined(__FreeBSD__) || defined(_ARM64_)
DWORD64 curPc;
#endif
#if UNWIND_CONTEXT_IS_UCONTEXT_T
WinContextToUnwindContext(context, &unwContext);
#else
st = unw_getcontext(&unwContext);
if (st < 0)
{
return FALSE;
}
#endif
st = unw_init_local(&cursor, &unwContext);
if (st < 0)
{
return FALSE;
}
#if !UNWIND_CONTEXT_IS_UCONTEXT_T
// Set the unwind context to the specified windows context
WinContextToUnwindCursor(context, &cursor);
#endif
#if defined(__APPLE__) || defined(__FreeBSD__) || defined(_ARM64_)
// OSX and FreeBSD appear to do two different things when unwinding
// 1: If it reaches where it cannot unwind anymore, say a
// managed frame. It wil return 0, but also update the $pc
// 2: If it unwinds all the way to _start it will return
// 0 from the step, but $pc will stay the same.
// The behaviour of libunwind from nongnu.org is to null the PC
// So we bank the original PC here, so we can compare it after
// the step
curPc = GetPc(context);
#endif
st = unw_step(&cursor);
if (st < 0)
{
return FALSE;
}
// Update the passed in windows context to reflect the unwind
//
UnwindContextToWinContext(&cursor, context);
#if defined(__APPLE__) || defined(__FreeBSD__) || defined(_ARM64_)
if (st == 0 && GetPc(context) == curPc)
{
SetPc(context, 0);
}
#endif
if (contextPointers != NULL)
{
GetContextPointers(&cursor, &unwContext, contextPointers);
}
return TRUE;
}