vfs: check userland buffers before reading them.

[haiku.git] / headers / libs / libcxxrt / dwarf_eh.h

/* 
 * Copyright 2010-2011 PathScale, Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS
 * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
/**
 * dwarf_eh.h - Defines some helper functions for parsing DWARF exception
 * handling tables.
 *
 * This file contains various helper functions that are independent of the
 * language-specific code.  It can be used in any personality function for the
 * Itanium ABI.
 */
#include <assert.h>

// TODO: Factor out Itanium / ARM differences.  We probably want an itanium.h
// and arm.h that can be included by this file depending on the target ABI.

// _GNU_SOURCE must be defined for unwind.h to expose some of the functions
// that we want.  If it isn't, then we define it and undefine it to make sure
// that it doesn't impact the rest of the program.
#ifndef _GNU_SOURCE
#       define _GNU_SOURCE 1
#       include "unwind.h"
#       undef _GNU_SOURCE
#else
#       include "unwind.h"
#endif

#include <stdint.h>

/// Type used for pointers into DWARF data
typedef unsigned char *dw_eh_ptr_t;

// Flag indicating a signed quantity
#define DW_EH_PE_signed 0x08
/// DWARF data encoding types.  
enum dwarf_data_encoding
{
        /// Absolute pointer value
        DW_EH_PE_absptr   = 0x00,
        /// Unsigned, little-endian, base 128-encoded (variable length).
        DW_EH_PE_uleb128 = 0x01,
        /// Unsigned 16-bit integer.
        DW_EH_PE_udata2  = 0x02,
        /// Unsigned 32-bit integer.
        DW_EH_PE_udata4  = 0x03,
        /// Unsigned 64-bit integer.
        DW_EH_PE_udata8  = 0x04,
        /// Signed, little-endian, base 128-encoded (variable length)
        DW_EH_PE_sleb128 = DW_EH_PE_uleb128 | DW_EH_PE_signed,
        /// Signed 16-bit integer.
        DW_EH_PE_sdata2  = DW_EH_PE_udata2 | DW_EH_PE_signed,
        /// Signed 32-bit integer.
        DW_EH_PE_sdata4  = DW_EH_PE_udata4 | DW_EH_PE_signed,
        /// Signed 32-bit integer.
        DW_EH_PE_sdata8  = DW_EH_PE_udata8 | DW_EH_PE_signed
};

/**
 * Returns the encoding for a DWARF EH table entry.  The encoding is stored in
 * the low four of an octet.  The high four bits store the addressing mode.
 */
static inline enum dwarf_data_encoding get_encoding(unsigned char x)
{
        return static_cast<enum dwarf_data_encoding>(x & 0xf);
}

/**
 * DWARF addressing mode constants.  When reading a pointer value from a DWARF
 * exception table, you must know how it is stored and what the addressing mode
 * is.  The low four bits tell you the encoding, allowing you to decode a
 * number.  The high four bits tell you the addressing mode, allowing you to
 * turn that number into an address in memory.
 */
enum dwarf_data_relative
{
        /// Value is omitted
        DW_EH_PE_omit     = 0xff,
        /// Value relative to program counter
        DW_EH_PE_pcrel    = 0x10,
        /// Value relative to the text segment
        DW_EH_PE_textrel  = 0x20,
        /// Value relative to the data segment
        DW_EH_PE_datarel  = 0x30,
        /// Value relative to the start of the function
        DW_EH_PE_funcrel  = 0x40,
        /// Aligned pointer (Not supported yet - are they actually used?)
        DW_EH_PE_aligned  = 0x50,
        /// Pointer points to address of real value
        DW_EH_PE_indirect = 0x80
};
/**
 * Returns the addressing mode component of this encoding.
 */
static inline enum dwarf_data_relative get_base(unsigned char x)
{
        return static_cast<enum dwarf_data_relative>(x & 0x70);
}
/**
 * Returns whether an encoding represents an indirect address.
 */
static int is_indirect(unsigned char x)
{
        return ((x & DW_EH_PE_indirect) == DW_EH_PE_indirect);
}

/**
 * Returns the size of a fixed-size encoding.  This function will abort if
 * called with a value that is not a fixed-size encoding.
 */
static inline int dwarf_size_of_fixed_size_field(unsigned char type)
{
        switch (get_encoding(type))
        {
                default: abort();
                case DW_EH_PE_sdata2: 
                case DW_EH_PE_udata2: return 2;
                case DW_EH_PE_sdata4:
                case DW_EH_PE_udata4: return 4;
                case DW_EH_PE_sdata8:
                case DW_EH_PE_udata8: return 8;
                case DW_EH_PE_absptr: return sizeof(void*);
        }
}

/** 
 * Read an unsigned, little-endian, base-128, DWARF value.  Updates *data to
 * point to the end of the value.  Stores the number of bits read in the value
 * pointed to by b, allowing you to determine the value of the highest bit, and
 * therefore the sign of a signed value.
 *
 * This function is not intended to be called directly.  Use read_sleb128() or
 * read_uleb128() for reading signed and unsigned versions, respectively.
 */
static uint64_t read_leb128(dw_eh_ptr_t *data, int *b)
{
        uint64_t uleb = 0;
        unsigned int bit = 0;
        unsigned char digit = 0;
        // We have to read at least one octet, and keep reading until we get to one
        // with the high bit unset
        do
        {
                // This check is a bit too strict - we should also check the highest
                // bit of the digit.
                assert(bit < sizeof(uint64_t) * 8);
                // Get the base 128 digit 
                digit = (**data) & 0x7f;
                // Add it to the current value
                uleb += digit << bit;
                // Increase the shift value
                bit += 7;
                // Proceed to the next octet
                (*data)++;
                // Terminate when we reach a value that does not have the high bit set
                // (i.e. which was not modified when we mask it with 0x7f)
        } while ((*(*data - 1)) != digit);
        *b = bit;

        return uleb;
}

/**
 * Reads an unsigned little-endian base-128 value starting at the address
 * pointed to by *data.  Updates *data to point to the next byte after the end
 * of the variable-length value.
 */
static int64_t read_uleb128(dw_eh_ptr_t *data)
{
        int b;
        return read_leb128(data, &b);
}

/**
 * Reads a signed little-endian base-128 value starting at the address pointed
 * to by *data.  Updates *data to point to the next byte after the end of the
 * variable-length value.
 */
static int64_t read_sleb128(dw_eh_ptr_t *data)
{
        int bits;
        // Read as if it's signed
        uint64_t uleb = read_leb128(data, &bits);
        // If the most significant bit read is 1, then we need to sign extend it
        if ((uleb >> (bits-1)) == 1)
        {
                // Sign extend by setting all bits in front of it to 1
                uleb |= static_cast<int64_t>(-1) << bits;
        }
        return static_cast<int64_t>(uleb);
}
/**
 * Reads a value using the specified encoding from the address pointed to by
 * *data.  Updates the value of *data to point to the next byte after the end
 * of the data.
 */
static uint64_t read_value(char encoding, dw_eh_ptr_t *data)
{
        enum dwarf_data_encoding type = get_encoding(encoding);
        switch (type)
        {
                // Read fixed-length types
#define READ(dwarf, type) \
                case dwarf:\
                {\
                        type t;\
                        memcpy(&t, *data, sizeof t);\
                        *data += sizeof t;\
                        return static_cast<uint64_t>(t);\
                }
                READ(DW_EH_PE_udata2, uint16_t)
                READ(DW_EH_PE_udata4, uint32_t)
                READ(DW_EH_PE_udata8, uint64_t)
                READ(DW_EH_PE_sdata2, int16_t)
                READ(DW_EH_PE_sdata4, int32_t)
                READ(DW_EH_PE_sdata8, int64_t)
                READ(DW_EH_PE_absptr, intptr_t)
#undef READ
                // Read variable-length types
                case DW_EH_PE_sleb128:
                        return read_sleb128(data);
                case DW_EH_PE_uleb128:
                        return read_uleb128(data);
                default: abort();
        }
}

/**
 * Resolves an indirect value.  This expects an unwind context, an encoding, a
 * decoded value, and the start of the region as arguments.  The returned value
 * is a pointer to the address identified by the encoded value.
 *
 * If the encoding does not specify an indirect value, then this returns v.
 */
static uint64_t resolve_indirect_value(_Unwind_Context *c,
                                       unsigned char encoding,
                                       int64_t v,
                                       dw_eh_ptr_t start)
{
        switch (get_base(encoding))
        {
                case DW_EH_PE_pcrel:
                        v += reinterpret_cast<uint64_t>(start);
                        break;
                case DW_EH_PE_textrel:
                        v += static_cast<uint64_t>(static_cast<uintptr_t>(_Unwind_GetTextRelBase(c)));
                        break;
                case DW_EH_PE_datarel:
                        v += static_cast<uint64_t>(static_cast<uintptr_t>(_Unwind_GetDataRelBase(c)));
                        break;
                case DW_EH_PE_funcrel:
                        v += static_cast<uint64_t>(static_cast<uintptr_t>(_Unwind_GetRegionStart(c)));
                default:
                        break;
        }
        // If this is an indirect value, then it is really the address of the real
        // value
        // TODO: Check whether this should really always be a pointer - it seems to
        // be a GCC extensions, so not properly documented...
        if (is_indirect(encoding))
        {
                v = static_cast<uint64_t>(reinterpret_cast<uintptr_t>(*reinterpret_cast<void**>(v)));
        }
        return v;
}


/**
 * Reads an encoding and a value, updating *data to point to the next byte.  
 */
static inline void read_value_with_encoding(_Unwind_Context *context,
                                            dw_eh_ptr_t *data,
                                            uint64_t *out)
{
        dw_eh_ptr_t start = *data;
        unsigned char encoding = *((*data)++);
        // If this value is omitted, skip it and don't touch the output value
        if (encoding == DW_EH_PE_omit) { return; }

        *out = read_value(encoding, data);
        *out = resolve_indirect_value(context, encoding, *out, start);
}

/**
 * Structure storing a decoded language-specific data area.  Use parse_lsda()
 * to generate an instance of this structure from the address returned by the
 * generic unwind library.  
 *
 * You should not need to inspect the fields of this structure directly if you
 * are just using this header.  The structure stores the locations of the
 * various tables used for unwinding exceptions and is used by the functions
 * for reading values from these tables.
 */
struct dwarf_eh_lsda
{
        /// The start of the region.  This is a cache of the value returned by
        /// _Unwind_GetRegionStart().
        dw_eh_ptr_t region_start;
        /// The start of the landing pads table.
        dw_eh_ptr_t landing_pads;
        /// The start of the type table.
        dw_eh_ptr_t type_table;
        /// The encoding used for entries in the type tables.
        unsigned char type_table_encoding;
        /// The location of the call-site table.
        dw_eh_ptr_t call_site_table;
        /// The location of the action table.
        dw_eh_ptr_t action_table;
        /// The encoding used for entries in the call-site table.
        unsigned char callsite_encoding;
};

/**
 * Parse the header on the language-specific data area and return a structure
 * containing the addresses and encodings of the various tables.
 */
static inline struct dwarf_eh_lsda parse_lsda(_Unwind_Context *context,
                                              unsigned char *data)
{
        struct dwarf_eh_lsda lsda;

        lsda.region_start = reinterpret_cast<dw_eh_ptr_t>(_Unwind_GetRegionStart(context));

        // If the landing pads are relative to anything other than the start of
        // this region, find out where.  This is @LPStart in the spec, although the
        // encoding that GCC uses does not quite match the spec.
        uint64_t v = static_cast<uint64_t>(reinterpret_cast<uintptr_t>(lsda.region_start));
        read_value_with_encoding(context, &data, &v);
        lsda.landing_pads = reinterpret_cast<dw_eh_ptr_t>(static_cast<uintptr_t>(v));

        // If there is a type table, find out where it is.  This is @TTBase in the
        // spec.  Note: we find whether there is a type table pointer by checking
        // whether the leading byte is DW_EH_PE_omit (0xff), which is not what the
        // spec says, but does seem to be how G++ indicates this.
        lsda.type_table = 0;
        lsda.type_table_encoding = *data++;
        if (lsda.type_table_encoding != DW_EH_PE_omit)
        {
                v = read_uleb128(&data);
                dw_eh_ptr_t type_table = data;
                type_table += v;
                lsda.type_table = type_table;
                //lsda.type_table = (uintptr_t*)(data + v);
        }
#if defined(__arm__) && !defined(__ARM_DWARF_EH__)
        lsda.type_table_encoding = (DW_EH_PE_pcrel | DW_EH_PE_indirect);
#endif

        lsda.callsite_encoding = static_cast<enum dwarf_data_encoding>(*(data++));

        // Action table is immediately after the call site table
        lsda.action_table = data;
        uintptr_t callsite_size = static_cast<uintptr_t>(read_uleb128(&data));
        lsda.action_table = data + callsite_size;
        // Call site table is immediately after the header
        lsda.call_site_table = static_cast<dw_eh_ptr_t>(data);


        return lsda;
}

/**
 * Structure representing an action to be performed while unwinding.  This
 * contains the address that should be unwound to and the action record that
 * provoked this action.
 */
struct dwarf_eh_action
{
        /** 
         * The address that this action directs should be the new program counter
         * value after unwinding.
         */
        dw_eh_ptr_t landing_pad;
        /// The address of the action record.
        dw_eh_ptr_t action_record;
};

/**
 * Look up the landing pad that corresponds to the current invoke.
 * Returns true if record exists.  The context is provided by the generic
 * unwind library and the lsda should be the result of a call to parse_lsda().
 *
 * The action record is returned via the result parameter.  
 */
static bool dwarf_eh_find_callsite(struct _Unwind_Context *context,
                                   struct dwarf_eh_lsda *lsda,
                                   struct dwarf_eh_action *result)
{
        result->action_record = 0;
        result->landing_pad = 0;
        // The current instruction pointer offset within the region
        uint64_t ip = _Unwind_GetIP(context) - _Unwind_GetRegionStart(context);
        unsigned char *callsite_table = static_cast<unsigned char*>(lsda->call_site_table);

        while (callsite_table <= lsda->action_table)
        {
                // Once again, the layout deviates from the spec.
                uint64_t call_site_start, call_site_size, landing_pad, action;
                call_site_start = read_value(lsda->callsite_encoding, &callsite_table);
                call_site_size = read_value(lsda->callsite_encoding, &callsite_table);

                // Call site entries are sorted, so if we find a call site that's after
                // the current instruction pointer then there is no action associated
                // with this call and we should unwind straight through this frame
                // without doing anything.
                if (call_site_start > ip) { break; }

                // Read the address of the landing pad and the action from the call
                // site table.
                landing_pad = read_value(lsda->callsite_encoding, &callsite_table);
                action = read_uleb128(&callsite_table);

                // We should not include the call_site_start (beginning of the region)
                // address in the ip range. For each call site:
                //
                // address1: call proc
                // address2: next instruction
                //
                // The call stack contains address2 and not address1, address1 can be
                // at the end of another EH region.
                if (call_site_start < ip && ip <= call_site_start + call_site_size)
                {
                        if (action)
                        {
                                // Action records are 1-biased so both no-record and zeroth
                                // record can be stored.
                                result->action_record = lsda->action_table + action - 1;
                        }
                        // No landing pad means keep unwinding.
                        if (landing_pad)
                        {
                                // Landing pad is the offset from the value in the header
                                result->landing_pad = lsda->landing_pads + landing_pad;
                        }
                        return true;
                }
        }
        return false;
}

/// Defines an exception class from 8 bytes (endian independent)
#define EXCEPTION_CLASS(a,b,c,d,e,f,g,h) \
        ((static_cast<uint64_t>(a) << 56) +\
         (static_cast<uint64_t>(b) << 48) +\
         (static_cast<uint64_t>(c) << 40) +\
         (static_cast<uint64_t>(d) << 32) +\
         (static_cast<uint64_t>(e) << 24) +\
         (static_cast<uint64_t>(f) << 16) +\
         (static_cast<uint64_t>(g) << 8) +\
         (static_cast<uint64_t>(h)))

#define GENERIC_EXCEPTION_CLASS(e,f,g,h) \
         (static_cast<uint32_t>(e) << 24) +\
         (static_cast<uint32_t>(f) << 16) +\
         (static_cast<uint32_t>(g) << 8) +\
         (static_cast<uint32_t>(h))