Significant disambiguation between host and target. (#10969)

[mono-project.git] / mono / mini / exceptions-x86.c

/**
 * \file
 * exception support for x86
 *
 * Authors:
 *   Dietmar Maurer (dietmar@ximian.com)
 *
 * (C) 2001 Ximian, Inc.
 */

#include <config.h>

#include <glib.h>
#include <signal.h>
#include <string.h>
#ifdef HAVE_UCONTEXT_H
#include <ucontext.h>
#endif

#include <mono/metadata/abi-details.h>
#include <mono/arch/x86/x86-codegen.h>
#include <mono/metadata/appdomain.h>
#include <mono/metadata/tabledefs.h>
#include <mono/metadata/threads.h>
#include <mono/metadata/debug-helpers.h>
#include <mono/metadata/exception.h>
#include <mono/metadata/gc-internals.h>
#include <mono/metadata/mono-debug.h>
#include <mono/utils/mono-mmap.h>

#include "mini.h"
#include "mini-x86.h"
#include "mini-runtime.h"
#include "tasklets.h"
#include "aot-runtime.h"

static gpointer signal_exception_trampoline;

gpointer
mono_x86_get_signal_exception_trampoline (MonoTrampInfo **info, gboolean aot);

#ifdef TARGET_WIN32
static void (*restore_stack) (void *);

static MonoW32ExceptionHandler fpe_handler;
static MonoW32ExceptionHandler ill_handler;
static MonoW32ExceptionHandler segv_handler;

LPTOP_LEVEL_EXCEPTION_FILTER mono_old_win_toplevel_exception_filter;
gpointer mono_win_vectored_exception_handle;
extern int (*gUnhandledExceptionHandler)(EXCEPTION_POINTERS*);

#ifndef PROCESS_CALLBACK_FILTER_ENABLED
#       define PROCESS_CALLBACK_FILTER_ENABLED 1
#endif

#define W32_SEH_HANDLE_EX(_ex) \
        if (_ex##_handler) _ex##_handler(0, ep, ctx)

LONG CALLBACK seh_unhandled_exception_filter(EXCEPTION_POINTERS* ep)
{
#ifndef MONO_CROSS_COMPILE
        if (mono_old_win_toplevel_exception_filter) {
                return (*mono_old_win_toplevel_exception_filter)(ep);
        }
#endif

        mono_handle_native_crash ("SIGSEGV", NULL, NULL);

        return EXCEPTION_CONTINUE_SEARCH;
}

/*
 * mono_win32_get_handle_stackoverflow (void):
 *
 * Returns a pointer to a method which restores the current context stack
 * and calls handle_exceptions, when done restores the original stack.
 */
static gpointer
mono_win32_get_handle_stackoverflow (void)
{
        static guint8 *start = NULL;
        guint8 *code;

        if (start)
                return start;

        /* restore_contect (void *sigctx) */
        start = code = mono_global_codeman_reserve (128);

        /* load context into ebx */
        x86_mov_reg_membase (code, X86_EBX, X86_ESP, 4, 4);

        /* move current stack into edi for later restore */
        x86_mov_reg_reg (code, X86_EDI, X86_ESP);

        /* use the new freed stack from sigcontext */
        /* XXX replace usage of struct sigcontext with MonoContext so we can use MONO_STRUCT_OFFSET */
        x86_mov_reg_membase (code, X86_ESP, X86_EBX,  G_STRUCT_OFFSET (struct sigcontext, esp), 4);

        /* get the current domain */
        x86_call_code (code, mono_domain_get);

        /* get stack overflow exception from domain object */
        x86_mov_reg_membase (code, X86_EAX, X86_EAX, G_STRUCT_OFFSET (MonoDomain, stack_overflow_ex), 4);

        /* call mono_arch_handle_exception (sctx, stack_overflow_exception_obj) */
        x86_push_reg (code, X86_EAX);
        x86_push_reg (code, X86_EBX);
        x86_call_code (code, mono_arch_handle_exception);

        /* restore the SEH handler stack */
        x86_mov_reg_reg (code, X86_ESP, X86_EDI);

        /* return */
        x86_ret (code);

        mono_arch_flush_icache (start, code - start);
        MONO_PROFILER_RAISE (jit_code_buffer, (start, code - start, MONO_PROFILER_CODE_BUFFER_EXCEPTION_HANDLING, NULL));

        return start;
}

/* Special hack to workaround the fact that the
 * when the SEH handler is called the stack is
 * to small to recover.
 *
 * Stack walking part of this method is from mono_handle_exception
 *
 * The idea is simple; 
 *  - walk the stack to free some space (64k)
 *  - set esp to new stack location
 *  - call mono_arch_handle_exception with stack overflow exception
 *  - set esp to SEH handlers stack
 *  - done
 */
static void 
win32_handle_stack_overflow (EXCEPTION_POINTERS* ep, CONTEXT *sctx)
{
        SYSTEM_INFO si;
        DWORD page_size;
        MonoDomain *domain = mono_domain_get ();
        MonoJitInfo rji;
        MonoJitTlsData *jit_tls = mono_tls_get_jit_tls ();
        MonoLMF *lmf = jit_tls->lmf;            
        MonoContext initial_ctx;
        MonoContext ctx;
        guint32 free_stack = 0;
        StackFrameInfo frame;

        mono_sigctx_to_monoctx (sctx, &ctx);
        
        /* get our os page size */
        GetSystemInfo(&si);
        page_size = si.dwPageSize;

        /* Let's walk the stack to recover
         * the needed stack space (if possible)
         */
        memset (&rji, 0, sizeof (rji));

        initial_ctx = ctx;
        free_stack = (guint8*)(MONO_CONTEXT_GET_BP (&ctx)) - (guint8*)(MONO_CONTEXT_GET_BP (&initial_ctx));

        /* try to free 64kb from our stack */
        do {
                MonoContext new_ctx;

                mono_arch_unwind_frame (domain, jit_tls, &rji, &ctx, &new_ctx, &lmf, NULL, &frame);
                if (!frame.ji) {
                        g_warning ("Exception inside function without unwind info");
                        g_assert_not_reached ();
                }

                if (frame.ji != (gpointer)-1) {
                        free_stack = (guint8*)(MONO_CONTEXT_GET_BP (&ctx)) - (guint8*)(MONO_CONTEXT_GET_BP (&initial_ctx));
                }

                /* todo: we should call abort if ji is -1 */
                ctx = new_ctx;
        } while (free_stack < 64 * 1024 && frame.ji != (gpointer) -1);

        mono_monoctx_to_sigctx (&ctx, sctx);

        /* todo: install new stack-guard page */

        /* use the new stack and call mono_arch_handle_exception () */
        restore_stack (sctx);
}

/*
 * Unhandled Exception Filter
 * Top-level per-process exception handler.
 */
LONG CALLBACK seh_vectored_exception_handler(EXCEPTION_POINTERS* ep)
{
        EXCEPTION_RECORD* er;
        CONTEXT* ctx;
        LONG res;
        MonoJitTlsData *jit_tls = mono_tls_get_jit_tls ();

        /* If the thread is not managed by the runtime return early */
        if (!jit_tls)
                return EXCEPTION_CONTINUE_SEARCH;

        jit_tls->mono_win_chained_exception_needs_run = FALSE;
        res = EXCEPTION_CONTINUE_EXECUTION;

        er = ep->ExceptionRecord;
        ctx = ep->ContextRecord;

        switch (er->ExceptionCode) {
        case EXCEPTION_STACK_OVERFLOW:
                win32_handle_stack_overflow (ep, ctx);
                break;
        case EXCEPTION_ACCESS_VIOLATION:
                W32_SEH_HANDLE_EX(segv);
                break;
        case EXCEPTION_ILLEGAL_INSTRUCTION:
                W32_SEH_HANDLE_EX(ill);
                break;
        case EXCEPTION_INT_DIVIDE_BY_ZERO:
        case EXCEPTION_INT_OVERFLOW:
        case EXCEPTION_FLT_DIVIDE_BY_ZERO:
        case EXCEPTION_FLT_OVERFLOW:
        case EXCEPTION_FLT_UNDERFLOW:
        case EXCEPTION_FLT_INEXACT_RESULT:
                W32_SEH_HANDLE_EX(fpe);
                break;
        default:
                jit_tls->mono_win_chained_exception_needs_run = TRUE;
                break;
        }

        if (jit_tls->mono_win_chained_exception_needs_run) {
                /* Don't copy context back if we chained exception
                * as the handler may have modfied the EXCEPTION_POINTERS
                * directly. We don't pass sigcontext to chained handlers.
                * Return continue search so the UnhandledExceptionFilter
                * can correctly chain the exception.
                */
                res = EXCEPTION_CONTINUE_SEARCH;
        }

        return res;
}

void win32_seh_init()
{
        /* install restore stack helper */
        if (!restore_stack)
                restore_stack = (void (*) (void*))mono_win32_get_handle_stackoverflow ();

        mono_old_win_toplevel_exception_filter = SetUnhandledExceptionFilter(seh_unhandled_exception_filter);
        mono_win_vectored_exception_handle = AddVectoredExceptionHandler (1, seh_vectored_exception_handler);
}

void win32_seh_cleanup()
{
        if (mono_old_win_toplevel_exception_filter)
                SetUnhandledExceptionFilter(mono_old_win_toplevel_exception_filter);
        RemoveVectoredExceptionHandler (mono_win_vectored_exception_handle);
}

void win32_seh_set_handler(int type, MonoW32ExceptionHandler handler)
{
        switch (type) {
        case SIGFPE:
                fpe_handler = handler;
                break;
        case SIGILL:
                ill_handler = handler;
                break;
        case SIGSEGV:
                segv_handler = handler;
                break;
        default:
                break;
        }
}

#endif /* TARGET_WIN32 */

/*
 * mono_arch_get_restore_context:
 *
 * Returns a pointer to a method which restores a previously saved sigcontext.
 */
gpointer
mono_arch_get_restore_context (MonoTrampInfo **info, gboolean aot)
{
        guint8 *start = NULL;
        guint8 *code;
        MonoJumpInfo *ji = NULL;
        GSList *unwind_ops = NULL;

        /* restore_contect (MonoContext *ctx) */

        start = code = mono_global_codeman_reserve (128);
        
        /* load ctx */
        x86_mov_reg_membase (code, X86_EAX, X86_ESP, 4, 4);

        /* restore EBX */
        x86_mov_reg_membase (code, X86_EBX, X86_EAX,  MONO_STRUCT_OFFSET (MonoContext, ebx), 4);

        /* restore EDI */
        x86_mov_reg_membase (code, X86_EDI, X86_EAX,  MONO_STRUCT_OFFSET (MonoContext, edi), 4);

        /* restore ESI */
        x86_mov_reg_membase (code, X86_ESI, X86_EAX,  MONO_STRUCT_OFFSET (MonoContext, esi), 4);

        /* restore EDX */
        x86_mov_reg_membase (code, X86_EDX, X86_EAX,  MONO_STRUCT_OFFSET (MonoContext, edx), 4);

        /*
         * The context resides on the stack, in the stack frame of the
         * caller of this function.  The stack pointer that we need to
         * restore is potentially many stack frames higher up, so the
         * distance between them can easily be more than the red zone
         * size.  Hence the stack pointer can be restored only after
         * we have finished loading everything from the context.
         */

        /* load ESP into EBP */
        x86_mov_reg_membase (code, X86_EBP, X86_EAX,  MONO_STRUCT_OFFSET (MonoContext, esp), 4);
        /* load return address into ECX */
        x86_mov_reg_membase (code, X86_ECX, X86_EAX,  MONO_STRUCT_OFFSET (MonoContext, eip), 4);
        /* save the return addr to the restored stack - 4 */
        x86_mov_membase_reg (code, X86_EBP, -4, X86_ECX, 4);

        /* load EBP into ECX */
        x86_mov_reg_membase (code, X86_ECX, X86_EAX,  MONO_STRUCT_OFFSET (MonoContext, ebp), 4);
        /* save EBP to the restored stack - 8 */
        x86_mov_membase_reg (code, X86_EBP, -8, X86_ECX, 4);

        /* load EAX into ECX */
        x86_mov_reg_membase (code, X86_ECX, X86_EAX,  MONO_STRUCT_OFFSET (MonoContext, eax), 4);
        /* save EAX to the restored stack - 12 */
        x86_mov_membase_reg (code, X86_EBP, -12, X86_ECX, 4);

        /* restore ECX */
        x86_mov_reg_membase (code, X86_ECX, X86_EAX,  MONO_STRUCT_OFFSET (MonoContext, ecx), 4);

        /* restore ESP - 12 */
        x86_lea_membase (code, X86_ESP, X86_EBP, -12);
        /* restore EAX */
        x86_pop_reg (code, X86_EAX);
        /* restore EBP */
        x86_pop_reg (code, X86_EBP);
        /* jump to the saved IP */
        x86_ret (code);

        if (info)
                *info = mono_tramp_info_create ("restore_context", start, code - start, ji, unwind_ops);
        else {
                GSList *l;

                for (l = unwind_ops; l; l = l->next)
                        g_free (l->data);
                g_slist_free (unwind_ops);
        }

        mono_arch_flush_icache (start, code - start);
        MONO_PROFILER_RAISE (jit_code_buffer, (start, code - start, MONO_PROFILER_CODE_BUFFER_EXCEPTION_HANDLING, NULL));

        return start;
}

/*
 * mono_arch_get_call_filter:
 *
 * Returns a pointer to a method which calls an exception filter. We
 * also use this function to call finally handlers (we pass NULL as 
 * @exc object in this case).
 */
gpointer
mono_arch_get_call_filter (MonoTrampInfo **info, gboolean aot)
{
        guint8* start;
        guint8 *code;
        MonoJumpInfo *ji = NULL;
        GSList *unwind_ops = NULL;
        guint kMaxCodeSize = 64;

        /* call_filter (MonoContext *ctx, unsigned long eip) */
        start = code = mono_global_codeman_reserve (kMaxCodeSize);

        x86_push_reg (code, X86_EBP);
        x86_mov_reg_reg (code, X86_EBP, X86_ESP);
        x86_push_reg (code, X86_EBX);
        x86_push_reg (code, X86_EDI);
        x86_push_reg (code, X86_ESI);

        /* load ctx */
        x86_mov_reg_membase (code, X86_EAX, X86_EBP, 8, 4);
        /* load eip */
        x86_mov_reg_membase (code, X86_ECX, X86_EBP, 12, 4);
        /* save EBP */
        x86_push_reg (code, X86_EBP);

        /* set new EBP */
        x86_mov_reg_membase (code, X86_EBP, X86_EAX,  MONO_STRUCT_OFFSET (MonoContext, ebp), 4);
        /* restore registers used by global register allocation (EBX & ESI) */
        x86_mov_reg_membase (code, X86_EBX, X86_EAX,  MONO_STRUCT_OFFSET (MonoContext, ebx), 4);
        x86_mov_reg_membase (code, X86_ESI, X86_EAX,  MONO_STRUCT_OFFSET (MonoContext, esi), 4);
        x86_mov_reg_membase (code, X86_EDI, X86_EAX,  MONO_STRUCT_OFFSET (MonoContext, edi), 4);

        /* align stack and save ESP */
        x86_mov_reg_reg (code, X86_EDX, X86_ESP);
        x86_alu_reg_imm (code, X86_AND, X86_ESP, -MONO_ARCH_FRAME_ALIGNMENT);
        g_assert (MONO_ARCH_FRAME_ALIGNMENT >= 8);
        x86_alu_reg_imm (code, X86_SUB, X86_ESP, MONO_ARCH_FRAME_ALIGNMENT - 8);
        x86_push_reg (code, X86_EDX);

        /* call the handler */
        x86_call_reg (code, X86_ECX);

        /* restore ESP */
        x86_pop_reg (code, X86_ESP);

        /* restore EBP */
        x86_pop_reg (code, X86_EBP);

        /* restore saved regs */
        x86_pop_reg (code, X86_ESI);
        x86_pop_reg (code, X86_EDI);
        x86_pop_reg (code, X86_EBX);
        x86_leave (code);
        x86_ret (code);

        if (info)
                *info = mono_tramp_info_create ("call_filter", start, code - start, ji, unwind_ops);
        else {
                GSList *l;

                for (l = unwind_ops; l; l = l->next)
                        g_free (l->data);
                g_slist_free (unwind_ops);
        }

        mono_arch_flush_icache (start, code - start);
        MONO_PROFILER_RAISE (jit_code_buffer, (start, code - start, MONO_PROFILER_CODE_BUFFER_EXCEPTION_HANDLING, NULL));

        g_assert ((code - start) < kMaxCodeSize);
        return start;
}

/*
 * mono_x86_throw_exception:
 *
 *   C function called from the throw trampolines.
 */
void
mono_x86_throw_exception (host_mgreg_t *regs, MonoObject *exc,
                                                  host_mgreg_t eip, gboolean rethrow, gboolean preserve_ips)
{
        ERROR_DECL (error);
        MonoContext ctx;

        ctx.esp = regs [X86_ESP];
        ctx.eip = eip;
        ctx.ebp = regs [X86_EBP];
        ctx.edi = regs [X86_EDI];
        ctx.esi = regs [X86_ESI];
        ctx.ebx = regs [X86_EBX];
        ctx.edx = regs [X86_EDX];
        ctx.ecx = regs [X86_ECX];
        ctx.eax = regs [X86_EAX];

#ifdef __APPLE__
        /* The OSX ABI specifies 16 byte alignment at call sites */
        g_assert ((ctx.esp % MONO_ARCH_FRAME_ALIGNMENT) == 0);
#endif

        if (mono_object_isinst_checked (exc, mono_defaults.exception_class, error)) {
                MonoException *mono_ex = (MonoException*)exc;
                if (!rethrow) {
                        mono_ex->stack_trace = NULL;
                        mono_ex->trace_ips = NULL;
                } else if (preserve_ips) {
                        mono_ex->caught_in_unmanaged = TRUE;
                }
        }
        mono_error_assert_ok (error);

        /* adjust eip so that it point into the call instruction */
        ctx.eip -= 1;

        mono_handle_exception (&ctx, exc);

        mono_restore_context (&ctx);

        g_assert_not_reached ();
}

void
mono_x86_throw_corlib_exception (host_mgreg_t *regs, guint32 ex_token_index, 
                                                                 host_mgreg_t eip, gint32 pc_offset)
{
        guint32 ex_token = MONO_TOKEN_TYPE_DEF | ex_token_index;
        MonoException *ex;

        ex = mono_exception_from_token (m_class_get_image (mono_defaults.exception_class), ex_token);

        eip -= pc_offset;

        /* Negate the ip adjustment done in mono_x86_throw_exception () */
        eip += 1;

        mono_x86_throw_exception (regs, (MonoObject*)ex, eip, FALSE, FALSE);
}

static void
mono_x86_resume_unwind (host_mgreg_t *regs, MonoObject *exc, 
                                                host_mgreg_t eip, gboolean rethrow)
{
        MonoContext ctx;

        ctx.esp = regs [X86_ESP];
        ctx.eip = eip;
        ctx.ebp = regs [X86_EBP];
        ctx.edi = regs [X86_EDI];
        ctx.esi = regs [X86_ESI];
        ctx.ebx = regs [X86_EBX];
        ctx.edx = regs [X86_EDX];
        ctx.ecx = regs [X86_ECX];
        ctx.eax = regs [X86_EAX];

        mono_resume_unwind (&ctx);
}

/*
 * get_throw_trampoline:
 *
 *  Generate a call to mono_x86_throw_exception/
 * mono_x86_throw_corlib_exception.
 * If LLVM is true, generate code which assumes the caller is LLVM generated code, 
 * which doesn't push the arguments.
 */
static guint8*
get_throw_trampoline (const char *name, gboolean rethrow, gboolean llvm, gboolean corlib, gboolean llvm_abs, gboolean resume_unwind, MonoTrampInfo **info, gboolean aot, gboolean preserve_ips)
{
        guint8 *start, *code, *labels [16];
        int i, stack_size, stack_offset, arg_offsets [5], regs_offset;
        MonoJumpInfo *ji = NULL;
        GSList *unwind_ops = NULL;
        guint kMaxCodeSize = 192;

        start = code = mono_global_codeman_reserve (kMaxCodeSize);

        stack_size = 128;

        /* 
         * On apple, the stack is misaligned by the pushing of the return address.
         */
        if (!llvm && corlib)
                /* On OSX, we don't generate alignment code to save space */
                stack_size += 4;
        else
                stack_size += MONO_ARCH_FRAME_ALIGNMENT - 4;

        /*
         * The stack looks like this:
         * <pc offset> (only if corlib is TRUE)
         * <exception object>/<type token>
         * <return addr> <- esp (unaligned on apple)
         */

        unwind_ops = mono_arch_get_cie_program ();

        /* Alloc frame */
        x86_alu_reg_imm (code, X86_SUB, X86_ESP, stack_size);
        mono_add_unwind_op_def_cfa_offset (unwind_ops, code, start, stack_size + 4);

        arg_offsets [0] = 0;
        arg_offsets [1] = 4;
        arg_offsets [2] = 8;
        arg_offsets [3] = 12;
        arg_offsets [4] = 16;
        regs_offset = 20;

        /* Save registers */
        for (i = 0; i < X86_NREG; ++i)
                if (i != X86_ESP)
                        x86_mov_membase_reg (code, X86_ESP, regs_offset + (i * 4), i, 4);
        /* Calculate the offset between the current sp and the sp of the caller */
        if (llvm) {
                /* LLVM doesn't push the arguments */
                stack_offset = stack_size + 4;
        } else {
                if (corlib) {
                        /* Two arguments */
                        stack_offset = stack_size + 4 + 8;
#ifdef __APPLE__
                        /* We don't generate stack alignment code on osx to save space */
#endif
                } else {
                        /* One argument + stack alignment */
                        stack_offset = stack_size + 4 + 4;
#ifdef __APPLE__
                        /* Pop the alignment added by OP_THROW too */
                        stack_offset += MONO_ARCH_FRAME_ALIGNMENT - 4;
#else
                        if (mono_do_x86_stack_align)
                                stack_offset += MONO_ARCH_FRAME_ALIGNMENT - 4;
#endif
                }
        }
        /* Save ESP */
        x86_lea_membase (code, X86_EAX, X86_ESP, stack_offset);
        x86_mov_membase_reg (code, X86_ESP, regs_offset + (X86_ESP * 4), X86_EAX, 4);

        /* Clear fp stack */
        labels [0] = code;
        x86_fnstsw (code);
        x86_shift_reg_imm (code, X86_SHR, X86_EAX, 11);
        x86_alu_reg_imm (code, X86_AND, X86_EAX, 7);
        x86_alu_reg_imm (code, X86_CMP, X86_EAX, 0);
        labels [1] = code;
        x86_branch8 (code, X86_CC_EQ, 0, FALSE);
        x86_fstp (code, 0);
        x86_jump_code (code, labels [0]);
        mono_x86_patch (labels [1], code);

        /* Set arg1 == regs */
        x86_lea_membase (code, X86_EAX, X86_ESP, regs_offset);
        x86_mov_membase_reg (code, X86_ESP, arg_offsets [0], X86_EAX, 4);
        /* Set arg2 == exc/ex_token_index */
        if (resume_unwind)
                x86_mov_reg_imm (code, X86_EAX, 0);
        else
                x86_mov_reg_membase (code, X86_EAX, X86_ESP, stack_size + 4, 4);
        x86_mov_membase_reg (code, X86_ESP, arg_offsets [1], X86_EAX, 4);
        /* Set arg3 == eip */
        if (llvm_abs)
                x86_alu_reg_reg (code, X86_XOR, X86_EAX, X86_EAX);
        else
                x86_mov_reg_membase (code, X86_EAX, X86_ESP, stack_size, 4);
        x86_mov_membase_reg (code, X86_ESP, arg_offsets [2], X86_EAX, 4);
        /* Set arg4 == rethrow/pc_offset */
        if (resume_unwind) {
                x86_mov_membase_imm (code, X86_ESP, arg_offsets [3], 0, 4);
        } else if (corlib) {
                x86_mov_reg_membase (code, X86_EAX, X86_ESP, stack_size + 8, 4);
                if (llvm_abs) {
                        /* 
                         * The caller is LLVM code which passes the absolute address not a pc offset,
                         * so compensate by passing 0 as 'ip' and passing the negated abs address as
                         * the pc offset.
                         */
                        x86_neg_reg (code, X86_EAX);
                }
                x86_mov_membase_reg (code, X86_ESP, arg_offsets [3], X86_EAX, 4);
        } else {
                x86_mov_membase_imm (code, X86_ESP, arg_offsets [3], rethrow, 4);

                /* Set arg4 == preserve_ips */
                x86_mov_membase_imm (code, X86_ESP, arg_offsets [4], preserve_ips, 4);
        }
        /* Make the call */
        if (aot) {
                // This can be called from runtime code, which can't guarantee that
                // ebx contains the got address.
                // So emit the got address loading code too
                code = mono_arch_emit_load_got_addr (start, code, NULL, &ji);
                code = mono_arch_emit_load_aotconst (start, code, &ji, MONO_PATCH_INFO_JIT_ICALL_ADDR, corlib ? "mono_x86_throw_corlib_exception" : "mono_x86_throw_exception");
                x86_call_reg (code, X86_EAX);
        } else {
                x86_call_code (code, resume_unwind ? (gpointer)(mono_x86_resume_unwind) : (corlib ? (gpointer)mono_x86_throw_corlib_exception : (gpointer)mono_x86_throw_exception));
        }
        x86_breakpoint (code);

        g_assert ((code - start) < kMaxCodeSize);

        if (info)
                *info = mono_tramp_info_create (name, start, code - start, ji, unwind_ops);
        else {
                GSList *l;

                for (l = unwind_ops; l; l = l->next)
                        g_free (l->data);
                g_slist_free (unwind_ops);
        }

        mono_arch_flush_icache (start, code - start);
        MONO_PROFILER_RAISE (jit_code_buffer, (start, code - start, MONO_PROFILER_CODE_BUFFER_EXCEPTION_HANDLING, NULL));

        return start;
}

/**
 * mono_arch_get_throw_exception:
 * \returns a function pointer which can be used to raise 
 * exceptions. The returned function has the following 
 * signature: void (*func) (MonoException *exc); 
 * For example to raise an arithmetic exception you can use:
 *
 * x86_push_imm (code, mono_get_exception_arithmetic ()); 
 * x86_call_code (code, arch_get_throw_exception ()); 
 *
 */
gpointer 
mono_arch_get_throw_exception (MonoTrampInfo **info, gboolean aot)
{
        return get_throw_trampoline ("throw_exception", FALSE, FALSE, FALSE, FALSE, FALSE, info, aot, FALSE);
}

gpointer 
mono_arch_get_rethrow_exception (MonoTrampInfo **info, gboolean aot)
{
        return get_throw_trampoline ("rethrow_exception", TRUE, FALSE, FALSE, FALSE, FALSE, info, aot, FALSE);
}

gpointer 
mono_arch_get_rethrow_preserve_exception (MonoTrampInfo **info, gboolean aot)
{
        return get_throw_trampoline ("rethrow_preserve_exception", TRUE, FALSE, FALSE, FALSE, FALSE, info, aot, TRUE);
}

/**
 * mono_arch_get_throw_corlib_exception:
 * \returns a function pointer which can be used to raise 
 * corlib exceptions. The returned function has the following 
 * signature: void (*func) (guint32 ex_token, guint32 offset); 
 * Here, offset is the offset which needs to be substracted from the caller IP 
 * to get the IP of the throw. Passing the offset has the advantage that it 
 * needs no relocations in the caller.
 */
gpointer 
mono_arch_get_throw_corlib_exception (MonoTrampInfo **info, gboolean aot)
{
        return get_throw_trampoline ("throw_corlib_exception", FALSE, FALSE, TRUE, FALSE, FALSE, info, aot, FALSE);
}

void
mono_arch_exceptions_init (void)
{
        guint8 *tramp;
        MonoTrampInfo *tinfo;

/* 
 * If we're running WoW64, we need to set the usermode exception policy 
 * for SEHs to behave. This requires hotfix http://support.microsoft.com/kb/976038
 * or (eventually) Windows 7 SP1.
 */
#ifdef TARGET_WIN32
        HMODULE kernel32 = LoadLibraryW (L"kernel32.dll");
        if (kernel32) {
                typedef BOOL (WINAPI * SetProcessUserModeExceptionPolicy_t) (DWORD dwFlags);
                typedef BOOL (WINAPI * GetProcessUserModeExceptionPolicy_t) (PDWORD dwFlags);
                GetProcessUserModeExceptionPolicy_t const getter = (GetProcessUserModeExceptionPolicy_t)GetProcAddress (kernel32, "GetProcessUserModeExceptionPolicy");
                if (getter) {
                        SetProcessUserModeExceptionPolicy_t const setter = (SetProcessUserModeExceptionPolicy_t)GetProcAddress (kernel32, "SetProcessUserModeExceptionPolicy");
                        if (setter) {
                                DWORD flags = 0;
                                if (getter (&flags))
                                        setter (flags & ~PROCESS_CALLBACK_FILTER_ENABLED);
                        }
                }
        }
#endif

        if (mono_aot_only) {
                signal_exception_trampoline = mono_aot_get_trampoline ("x86_signal_exception_trampoline");
                return;
        }

        /* LLVM needs different throw trampolines */
        tramp = get_throw_trampoline ("llvm_throw_exception_trampoline", FALSE, TRUE, FALSE, FALSE, FALSE, &tinfo, FALSE,  FALSE);
        mono_register_jit_icall (tramp, "llvm_throw_exception_trampoline", NULL, TRUE);
        mono_tramp_info_register (tinfo, NULL);

        tramp = get_throw_trampoline ("llvm_rethrow_exception_trampoline", TRUE, TRUE, FALSE, FALSE, FALSE, &tinfo, FALSE, FALSE);
        mono_register_jit_icall (tramp, "llvm_rethrow_exception_trampoline", NULL, TRUE);
        mono_tramp_info_register (tinfo, NULL);

        tramp = get_throw_trampoline ("llvm_throw_corlib_exception_trampoline", FALSE, TRUE, TRUE, FALSE, FALSE, &tinfo, FALSE, FALSE);
        mono_register_jit_icall (tramp, "llvm_throw_corlib_exception_trampoline", NULL, TRUE);
        mono_tramp_info_register (tinfo, NULL);

        tramp = get_throw_trampoline ("llvm_throw_corlib_exception_abs_trampoline", FALSE, TRUE, TRUE, TRUE, FALSE, &tinfo, FALSE, FALSE);
        mono_register_jit_icall (tramp, "llvm_throw_corlib_exception_abs_trampoline", NULL, TRUE);
        mono_tramp_info_register (tinfo, NULL);

        tramp = get_throw_trampoline ("llvm_resume_unwind_trampoline", FALSE, FALSE, FALSE, FALSE, TRUE, &tinfo, FALSE, FALSE);
        mono_register_jit_icall (tramp, "llvm_resume_unwind_trampoline", NULL, TRUE);
        mono_tramp_info_register (tinfo, NULL);

        signal_exception_trampoline = mono_x86_get_signal_exception_trampoline (&tinfo, FALSE);
        mono_tramp_info_register (tinfo, NULL);
}

/*
 * mono_arch_unwind_frame:
 *
 * See exceptions-amd64.c for docs.
 */
gboolean
mono_arch_unwind_frame (MonoDomain *domain, MonoJitTlsData *jit_tls, 
                                                         MonoJitInfo *ji, MonoContext *ctx, 
                                                         MonoContext *new_ctx, MonoLMF **lmf,
                                                         host_mgreg_t **save_locations,
                                                         StackFrameInfo *frame)
{
        gpointer ip = MONO_CONTEXT_GET_IP (ctx);

        memset (frame, 0, sizeof (StackFrameInfo));
        frame->ji = ji;

        *new_ctx = *ctx;

        if (ji != NULL) {
                host_mgreg_t regs [MONO_MAX_IREGS + 1];
                guint8 *cfa;
                guint32 unwind_info_len;
                guint8 *unwind_info;

                if (ji->is_trampoline)
                        frame->type = FRAME_TYPE_TRAMPOLINE;
                else
                        frame->type = FRAME_TYPE_MANAGED;

                unwind_info = mono_jinfo_get_unwind_info (ji, &unwind_info_len);

                regs [X86_EAX] = new_ctx->eax;
                regs [X86_EBX] = new_ctx->ebx;
                regs [X86_ECX] = new_ctx->ecx;
                regs [X86_EDX] = new_ctx->edx;
                regs [X86_ESP] = new_ctx->esp;
                regs [X86_EBP] = new_ctx->ebp;
                regs [X86_ESI] = new_ctx->esi;
                regs [X86_EDI] = new_ctx->edi;
                regs [X86_NREG] = new_ctx->eip;

                mono_unwind_frame ((guint8*)unwind_info, unwind_info_len, (guint8*)ji->code_start,
                                                   (guint8*)ji->code_start + ji->code_size,
                                                   (guint8*)ip, NULL, regs, MONO_MAX_IREGS + 1,
                                                   save_locations, MONO_MAX_IREGS, &cfa);

                new_ctx->eax = regs [X86_EAX];
                new_ctx->ebx = regs [X86_EBX];
                new_ctx->ecx = regs [X86_ECX];
                new_ctx->edx = regs [X86_EDX];
                new_ctx->esp = regs [X86_ESP];
                new_ctx->ebp = regs [X86_EBP];
                new_ctx->esi = regs [X86_ESI];
                new_ctx->edi = regs [X86_EDI];
                new_ctx->eip = regs [X86_NREG];

                /* The CFA becomes the new SP value */
                new_ctx->esp = (gssize)cfa;

                /* Adjust IP */
                new_ctx->eip --;

                return TRUE;
        } else if (*lmf) {
                g_assert ((((gsize)(*lmf)->previous_lmf) & 2) == 0);

                if ((ji = mini_jit_info_table_find (domain, (gpointer)(*lmf)->eip, NULL))) {
                        frame->ji = ji;
                } else {
                        if (!(*lmf)->method)
                                return FALSE;
                        frame->method = (*lmf)->method;
                }

                new_ctx->esi = (*lmf)->esi;
                new_ctx->edi = (*lmf)->edi;
                new_ctx->ebx = (*lmf)->ebx;
                new_ctx->ebp = (*lmf)->ebp;
                new_ctx->eip = (*lmf)->eip;

                /* Adjust IP */
                new_ctx->eip --;

                frame->type = FRAME_TYPE_MANAGED_TO_NATIVE;

                /* Check if we are in a trampoline LMF frame */
                if ((gsize)((*lmf)->previous_lmf) & 1) {
                        /* lmf->esp is set by the trampoline code */
                        new_ctx->esp = (*lmf)->esp;
                }
                else
                        /* the lmf is always stored on the stack, so the following
                         * expression points to a stack location which can be used as ESP */
                        new_ctx->esp = (unsigned long)&((*lmf)->eip);

                *lmf = (MonoLMF*)(((gsize)(*lmf)->previous_lmf) & ~3);

                return TRUE;
        }

        return FALSE;
}

gpointer
mono_arch_ip_from_context (void *sigctx)
{
#if defined(HOST_WATCHOS)
        printf("WARNING: mono_arch_ip_from_context() called!\n");
        return (NULL);
#elif defined(MONO_CROSS_COMPILE)
        g_assert_not_reached ();
        return NULL;
#elif defined(MONO_ARCH_USE_SIGACTION)
        ucontext_t *ctx = (ucontext_t*)sigctx;
        return (gpointer)UCONTEXT_REG_EIP (ctx);
#elif defined(HOST_WIN32)
        return (gpointer)((CONTEXT*)sigctx)->Eip;
#else
        struct sigcontext *ctx = sigctx;
        return (gpointer)ctx->SC_EIP;
#endif
}

/*
 * handle_exception:
 *
 *   Called by resuming from a signal handler.
 */
static void
handle_signal_exception (gpointer obj)
{
        MonoJitTlsData *jit_tls = mono_tls_get_jit_tls ();
        MonoContext ctx;

        memcpy (&ctx, &jit_tls->ex_ctx, sizeof (MonoContext));

        mono_handle_exception (&ctx, (MonoObject*)obj);

        mono_restore_context (&ctx);
}

/*
 * mono_x86_get_signal_exception_trampoline:
 *
 *   This x86 specific trampoline is used to call handle_signal_exception.
 */
gpointer
mono_x86_get_signal_exception_trampoline (MonoTrampInfo **info, gboolean aot)
{
        guint8 *start, *code;
        MonoJumpInfo *ji = NULL;
        GSList *unwind_ops = NULL;
        int stack_size;

        start = code = mono_global_codeman_reserve (128);

        /* FIXME no unwind before we push ip */
        /* Caller ip */
        x86_push_reg (code, X86_ECX);

        mono_add_unwind_op_def_cfa (unwind_ops, code, start, X86_ESP, 4);
        mono_add_unwind_op_offset (unwind_ops, code, start, X86_NREG, -4);

        /* Fix the alignment to be what apple expects */
        stack_size = 12;

        x86_alu_reg_imm (code, X86_SUB, X86_ESP, stack_size);
        mono_add_unwind_op_def_cfa_offset (unwind_ops, code, start, stack_size + 4);

        /* Arg1 */
        x86_mov_membase_reg (code, X86_ESP, 0, X86_EAX, 4);
        /* Branch to target */
        x86_call_reg (code, X86_EDX);

        g_assert ((code - start) < 128);

        if (info)
                *info = mono_tramp_info_create ("x86_signal_exception_trampoline", start, code - start, ji, unwind_ops);
        else {
                GSList *l;

                for (l = unwind_ops; l; l = l->next)
                        g_free (l->data);
                g_slist_free (unwind_ops);
        }

        mono_arch_flush_icache (start, code - start);
        MONO_PROFILER_RAISE (jit_code_buffer, (start, code - start, MONO_PROFILER_CODE_BUFFER_EXCEPTION_HANDLING, NULL));

        return start;
}


void
mono_arch_setup_async_callback (MonoContext *ctx, void (*async_cb)(void *fun), gpointer user_data)
{
        /*
         * Can't pass the obj on the stack, since we are executing on the
         * same stack. Can't save it into MonoJitTlsData, since it needs GC tracking.
         * So put it into a register, and branch to a trampoline which
         * pushes it.
         */
        ctx->eax = (host_mgreg_t)(gsize)user_data;
        ctx->ecx = ctx->eip;
        ctx->edx = (host_mgreg_t)(gsize)async_cb;

        /*align the stack*/
        ctx->esp = (ctx->esp - 16) & ~15;
        ctx->eip = (host_mgreg_t)(gsize)signal_exception_trampoline;
}

gboolean
mono_arch_handle_exception (void *sigctx, gpointer obj)
{
#if defined(MONO_ARCH_USE_SIGACTION)
        MonoContext mctx;
        ucontext_t *ctx = (ucontext_t*)sigctx;

        /*
         * Handling the exception in the signal handler is problematic, since the original
         * signal is disabled, and we could run arbitrary code though the debugger. So
         * resume into the normal stack and do most work there if possible.
         */
        MonoJitTlsData *jit_tls = mono_tls_get_jit_tls ();

        /* Pass the ctx parameter in TLS */
        mono_sigctx_to_monoctx (ctx, &jit_tls->ex_ctx);

        mctx = jit_tls->ex_ctx;
        mono_setup_async_callback (&mctx, handle_signal_exception, obj);
        mono_monoctx_to_sigctx (&mctx, sigctx);

        return TRUE;
#elif defined (TARGET_WIN32)
        MonoContext mctx;
        MonoJitTlsData *jit_tls = mono_tls_get_jit_tls ();

        mono_sigctx_to_monoctx (sigctx, &jit_tls->ex_ctx);

        mctx = jit_tls->ex_ctx;
        mono_setup_async_callback (&mctx, handle_signal_exception, obj);
        mono_monoctx_to_sigctx (&mctx, sigctx);

        return TRUE;
#else
        MonoContext mctx;

        mono_sigctx_to_monoctx (sigctx, &mctx);

        mono_handle_exception (&mctx, obj);

        mono_monoctx_to_sigctx (&mctx, sigctx);

        return TRUE;
#endif
}

static MonoObject*
restore_soft_guard_pages (void)
{
        MonoJitTlsData *jit_tls = mono_tls_get_jit_tls ();

        if (jit_tls->stack_ovf_guard_base)
                mono_mprotect (jit_tls->stack_ovf_guard_base, jit_tls->stack_ovf_guard_size, MONO_MMAP_NONE);

        if (jit_tls->stack_ovf_pending) {
                MonoDomain *domain = mono_domain_get ();
                jit_tls->stack_ovf_pending = 0;
                return (MonoObject *) domain->stack_overflow_ex;
        }
        return NULL;
}

/* 
 * this function modifies mctx so that when it is restored, it
 * won't execcute starting at mctx.eip, but in a function that
 * will restore the protection on the soft-guard pages and return back to
 * continue at mctx.eip.
 */
static void
prepare_for_guard_pages (MonoContext *mctx)
{
        gpointer *sp;
        sp = (gpointer*)(mctx->esp);
        sp -= 1;
        /* the return addr */
        sp [0] = (gpointer)(mctx->eip);
        mctx->eip = (unsigned long)restore_soft_guard_pages;
        mctx->esp = (unsigned long)sp;
}


static void
altstack_handle_and_restore (MonoContext *ctx, gpointer obj, gboolean stack_ovf)
{
        MonoContext mctx;

        mctx = *ctx;

        mono_handle_exception (&mctx, (MonoObject*)obj);
        if (stack_ovf) {
                MonoJitTlsData *jit_tls = mono_tls_get_jit_tls ();
                jit_tls->stack_ovf_pending = 1;
                prepare_for_guard_pages (&mctx);
        }
        mono_restore_context (&mctx);
}

void
mono_arch_handle_altstack_exception (void *sigctx, MONO_SIG_HANDLER_INFO_TYPE *siginfo, gpointer fault_addr, gboolean stack_ovf)
{
#if defined(MONO_ARCH_USE_SIGACTION) && !defined(MONO_CROSS_COMPILE)
        MonoException *exc = NULL;
        ucontext_t *ctx = (ucontext_t*)sigctx;
        MonoJitInfo *ji = mini_jit_info_table_find (mono_domain_get (), (gpointer)UCONTEXT_REG_EIP (ctx), NULL);
        gpointer *sp;
        int frame_size;

        /* if we didn't find a managed method for the ip address and it matches the fault
         * address, we assume we followed a broken pointer during an indirect call, so
         * we try the lookup again with the return address pushed on the stack
         */
        if (!ji && fault_addr == (gpointer)UCONTEXT_REG_EIP (ctx)) {
                glong *sp = (glong*)UCONTEXT_REG_ESP (ctx);
                ji = mini_jit_info_table_find (mono_domain_get (), (gpointer)sp [0], NULL);
                if (ji)
                        UCONTEXT_REG_EIP (ctx) = sp [0];
        }
        if (stack_ovf)
                exc = mono_domain_get ()->stack_overflow_ex;
        if (!ji)
                mono_handle_native_crash ("SIGSEGV", sigctx, siginfo);
        /* setup a call frame on the real stack so that control is returned there
         * and exception handling can continue.
         * If this was a stack overflow the caller already ensured the stack pages
         * needed have been unprotected.
         * The frame looks like:
         *   ucontext struct
         *   test_only arg
         *   exception arg
         *   ctx arg
         *   return ip
         */
        // FIXME: test_only is no more.
        frame_size = sizeof (MonoContext) + sizeof (gpointer) * 4;
        frame_size += 15;
        frame_size &= ~15;
        sp = (gpointer*)(UCONTEXT_REG_ESP (ctx) & ~15);
        sp = (gpointer*)((char*)sp - frame_size);
        /* the incoming arguments are aligned to 16 bytes boundaries, so the return address IP
         * goes at sp [-1]
         */
        sp [-1] = (gpointer)UCONTEXT_REG_EIP (ctx);
        sp [0] = sp + 4;
        sp [1] = exc;
        sp [2] = (gpointer)stack_ovf;
        mono_sigctx_to_monoctx (sigctx, (MonoContext*)(sp + 4));
        /* at the return form the signal handler execution starts in altstack_handle_and_restore() */
        UCONTEXT_REG_EIP (ctx) = (unsigned long)altstack_handle_and_restore;
        UCONTEXT_REG_ESP (ctx) = (unsigned long)(sp - 1);
#endif
}

#if MONO_SUPPORT_TASKLETS
MonoContinuationRestore
mono_tasklets_arch_restore (void)
{
        static guint8* saved = NULL;
        guint8 *code, *start;

        if (saved)
                return (MonoContinuationRestore)saved;
        code = start = mono_global_codeman_reserve (48);
        /* the signature is: restore (MonoContinuation *cont, int state, MonoLMF **lmf_addr) */
        /* put cont in edx */
        x86_mov_reg_membase (code, X86_EDX, X86_ESP, 4, 4);
        /* state in eax, so it's setup as the return value */
        x86_mov_reg_membase (code, X86_EAX, X86_ESP, 8, 4);
        /* lmf_addr in ebx */
        x86_mov_reg_membase(code, X86_EBX, X86_ESP, 0x0C, 4);

        /* setup the copy of the stack */
        x86_mov_reg_membase (code, X86_ECX, X86_EDX, MONO_STRUCT_OFFSET (MonoContinuation, stack_used_size), 4);
        x86_shift_reg_imm (code, X86_SHR, X86_ECX, 2);
        x86_cld (code);
        x86_mov_reg_membase (code, X86_ESI, X86_EDX, MONO_STRUCT_OFFSET (MonoContinuation, saved_stack), 4);
        x86_mov_reg_membase (code, X86_EDI, X86_EDX, MONO_STRUCT_OFFSET (MonoContinuation, return_sp), 4);
        x86_prefix (code, X86_REP_PREFIX);
        x86_movsl (code);

        /* now restore the registers from the LMF */
        x86_mov_reg_membase (code, X86_ECX, X86_EDX, MONO_STRUCT_OFFSET (MonoContinuation, lmf), 4);
        x86_mov_reg_membase (code, X86_EBP, X86_ECX, MONO_STRUCT_OFFSET (MonoLMF, ebp), 4);
        x86_mov_reg_membase (code, X86_ESP, X86_ECX, MONO_STRUCT_OFFSET (MonoLMF, esp), 4);

        /* restore the lmf chain */
        /*x86_mov_reg_membase (code, X86_ECX, X86_ESP, 12, 4);
        x86_mov_membase_reg (code, X86_ECX, 0, X86_EDX, 4);*/

        x86_jump_membase (code, X86_EDX, MONO_STRUCT_OFFSET (MonoContinuation, return_ip));

        mono_arch_flush_icache (start, code - start);
        MONO_PROFILER_RAISE (jit_code_buffer, (start, code - start, MONO_PROFILER_CODE_BUFFER_EXCEPTION_HANDLING, NULL));
        g_assert ((code - start) <= 48);

        saved = start;
        return (MonoContinuationRestore)saved;
}
#endif

/*
 * mono_arch_setup_resume_sighandler_ctx:
 *
 *   Setup CTX so execution continues at FUNC.
 */
void
mono_arch_setup_resume_sighandler_ctx (MonoContext *ctx, gpointer func)
{
        int align = (((gint32)MONO_CONTEXT_GET_SP (ctx)) % MONO_ARCH_FRAME_ALIGNMENT + 4);

        if (align != 0)
                MONO_CONTEXT_SET_SP (ctx, (gsize)MONO_CONTEXT_GET_SP (ctx) - align);

        MONO_CONTEXT_SET_IP (ctx, func);
}