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Diffstat (limited to 'contrib/libcxxrt/dwarf_eh.h')
| -rw-r--r-- | contrib/libcxxrt/dwarf_eh.h | 454 |
1 files changed, 454 insertions, 0 deletions
diff --git a/contrib/libcxxrt/dwarf_eh.h b/contrib/libcxxrt/dwarf_eh.h new file mode 100644 index 0000000..52e6369 --- /dev/null +++ b/contrib/libcxxrt/dwarf_eh.h @@ -0,0 +1,454 @@ +/** + * 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 +{ + /// 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 (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, + /// Absolute pointer value + DW_EH_PE_absptr = 0x00, + /// 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 (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 |= ((int64_t)-1) << bits; + } + return (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); + uint64_t v; + switch (type) + { + // Read fixed-length types +#define READ(dwarf, type) \ + case dwarf:\ + v = (uint64_t)(*(type*)(*data));\ + *data += sizeof(type);\ + break; + 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: + v = read_sleb128(data); + break; + case DW_EH_PE_uleb128: + v = read_uleb128(data); + break; + default: abort(); + } + + return v; +} + +/** + * 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 += (uint64_t)start; + break; + case DW_EH_PE_textrel: + v += (uint64_t)_Unwind_GetTextRelBase(c); + break; + case DW_EH_PE_datarel: + v += (uint64_t)_Unwind_GetDataRelBase(c); + break; + case DW_EH_PE_funcrel: + v += (uint64_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 = (uint64_t)(uintptr_t)*(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 = (dw_eh_ptr_t)(uintptr_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 = (uint64_t)(uintptr_t)lsda.region_start; + read_value_with_encoding(context, &data, &v); + lsda.landing_pads = (dw_eh_ptr_t)(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 __arm__ + lsda.type_table_encoding = (DW_EH_PE_pcrel | DW_EH_PE_indirect); +#endif + + lsda.callsite_encoding = (enum dwarf_data_encoding)(*(data++)); + + // Action table is immediately after the call site table + lsda.action_table = data; + uintptr_t callsite_size = (uintptr_t)read_uleb128(&data); + lsda.action_table = data + callsite_size; + // Call site table is immediately after the header + lsda.call_site_table = (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 = (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) \ + (((uint64_t)a << 56) +\ + ((uint64_t)b << 48) +\ + ((uint64_t)c << 40) +\ + ((uint64_t)d << 32) +\ + ((uint64_t)e << 24) +\ + ((uint64_t)f << 16) +\ + ((uint64_t)g << 8) +\ + ((uint64_t)h)) + +#define GENERIC_EXCEPTION_CLASS(e,f,g,h) \ + ((uint32_t)e << 24) +\ + ((uint32_t)f << 16) +\ + ((uint32_t)g << 8) +\ + ((uint32_t)h) |
