lib/gcc_personality_v0.c

//===-- gcc_personality_v0.c - Implement __gcc_personality_v0 -------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

//
// _Unwind_* stuff based on C++ ABI public documentation
// http://refspecs.freestandards.org/abi-eh-1.21.html
//
typedef enum {
    _URC_NO_REASON = 0,
    _URC_FOREIGN_EXCEPTION_CAUGHT = 1,
    _URC_FATAL_PHASE2_ERROR = 2,
    _URC_FATAL_PHASE1_ERROR = 3,
    _URC_NORMAL_STOP = 4,
    _URC_END_OF_STACK = 5,
    _URC_HANDLER_FOUND = 6,
    _URC_INSTALL_CONTEXT = 7,
    _URC_CONTINUE_UNWIND = 8
} _Unwind_Reason_Code;

typedef enum {
    _UA_SEARCH_PHASE = 1,
    _UA_CLEANUP_PHASE = 2,
    _UA_HANDLER_FRAME = 4,
    _UA_FORCE_UNWIND = 8,
    _UA_END_OF_STACK = 16
} _Unwind_Action;

typedef struct _Unwind_Context* _Unwind_Context_t;

struct _Unwind_Exception {
    uint64_t                exception_class;
    _Unwind_Reason_Code        (*exception_cleanup)(_Unwind_Reason_Code reason, 
                                                struct _Unwind_Exception* exc);
    uintptr_t                private_1;    
    uintptr_t                private_2;    
};

extern const uint8_t*    _Unwind_GetLanguageSpecificData(_Unwind_Context_t c);
extern void              _Unwind_SetGR(_Unwind_Context_t c, int i, uintptr_t n);
extern void              _Unwind_SetIP(_Unwind_Context_t, uintptr_t new_value);
extern uintptr_t         _Unwind_GetIP(_Unwind_Context_t context);
extern uintptr_t         _Unwind_GetRegionStart(_Unwind_Context_t context);


// 
// Pointer encodings documented at:
//   http://refspecs.freestandards.org/LSB_1.3.0/gLSB/gLSB/ehframehdr.html
//
#define DW_EH_PE_omit      0xff  // no data follows

#define DW_EH_PE_absptr    0x00
#define DW_EH_PE_uleb128   0x01
#define DW_EH_PE_udata2    0x02
#define DW_EH_PE_udata4    0x03
#define DW_EH_PE_udata8    0x04
#define DW_EH_PE_sleb128   0x09
#define DW_EH_PE_sdata2    0x0A
#define DW_EH_PE_sdata4    0x0B
#define DW_EH_PE_sdata8    0x0C

#define DW_EH_PE_pcrel     0x10
#define DW_EH_PE_textrel   0x20
#define DW_EH_PE_datarel   0x30
#define DW_EH_PE_funcrel   0x40
#define DW_EH_PE_aligned   0x50  
#define DW_EH_PE_indirect  0x80 // gcc extension



// read a uleb128 encoded value and advance pointer
static uintptr_t readULEB128(const uint8_t** data)
{
    uintptr_t result = 0;
    uintptr_t shift = 0;
    unsigned char byte;
    const uint8_t* p = *data;
    do {
        byte = *p++;
        result |= (byte & 0x7f) << shift;
        shift += 7;
    } while (byte & 0x80);
    *data = p;
    return result;
}

// read a pointer encoded value and advance pointer
static uintptr_t readEncodedPointer(const uint8_t** data, uint8_t encoding)
{
    const uint8_t* p = *data;
    uintptr_t result = 0;

    if ( encoding == DW_EH_PE_omit ) 
        return 0;

    // first get value
    switch (encoding & 0x0F) {
        case DW_EH_PE_absptr:
            result = *((uintptr_t*)p);
            p += sizeof(uintptr_t);
            break;
        case DW_EH_PE_uleb128:
            result = readULEB128(&p);
            break;
        case DW_EH_PE_udata2:
            result = *((uint16_t*)p);
            p += sizeof(uint16_t);
            break;
        case DW_EH_PE_udata4:
            result = *((uint32_t*)p);
            p += sizeof(uint32_t);
            break;
        case DW_EH_PE_udata8:
            result = *((uint64_t*)p);
            p += sizeof(uint64_t);
            break;
        case DW_EH_PE_sdata2:
            result = *((int16_t*)p);
            p += sizeof(int16_t);
            break;
        case DW_EH_PE_sdata4:
            result = *((int32_t*)p);
            p += sizeof(int32_t);
            break;
        case DW_EH_PE_sdata8:
            result = *((int64_t*)p);
            p += sizeof(int64_t);
            break;
        case DW_EH_PE_sleb128:
        default:
            // not supported
            abort();
            break;
    }

    // then add relative offset
    switch ( encoding & 0x70 ) {
        case DW_EH_PE_absptr:
            // do nothing
            break;
        case DW_EH_PE_pcrel:
            result += (uintptr_t)(*data);
            break;
        case DW_EH_PE_textrel:
        case DW_EH_PE_datarel:
        case DW_EH_PE_funcrel:
        case DW_EH_PE_aligned:
        default:
            // not supported
            abort();
            break;
    }

    // then apply indirection
    if (encoding & DW_EH_PE_indirect) {
        result = *((uintptr_t*)result);
    }

    *data = p;
    return result;
}


//
// The C compiler makes references to __gcc_personality_v0 in
// the dwarf unwind information for translation units that use
// __attribute__((cleanup(xx))) on local variables.
// This personality routine is called by the system unwinder
// on each frame as the stack is unwound during a C++ exception
// throw through a C function compiled with -fexceptions.
//
_Unwind_Reason_Code __gcc_personality_v0(int version, _Unwind_Action actions,
         uint64_t exceptionClass, struct _Unwind_Exception* exceptionObject,
         _Unwind_Context_t context)
{
    // Since C does not have catch clauses, there is nothing to do during
    // phase 1 (the search phase).
    if ( actions & _UA_SEARCH_PHASE ) 
        return _URC_CONTINUE_UNWIND;
        
    // There is nothing to do if there is no LSDA for this frame.
    const uint8_t* lsda = _Unwind_GetLanguageSpecificData(context);
    if ( lsda == NULL )
        return _URC_CONTINUE_UNWIND;

    uintptr_t pc = _Unwind_GetIP(context)-1;
    uintptr_t funcStart = _Unwind_GetRegionStart(context);
    uintptr_t pcOffset = pc - funcStart;

    // Parse LSDA header.
    uint8_t lpStartEncoding = *lsda++;
    if (lpStartEncoding != DW_EH_PE_omit) {
        readEncodedPointer(&lsda, lpStartEncoding); 
    }
    uint8_t ttypeEncoding = *lsda++;
    if (ttypeEncoding != DW_EH_PE_omit) {
        readULEB128(&lsda);  
    }
    // Walk call-site table looking for range that includes current PC.
    uint8_t         callSiteEncoding = *lsda++;
    uint32_t        callSiteTableLength = readULEB128(&lsda);
    const uint8_t*  callSiteTableStart = lsda;
    const uint8_t*  callSiteTableEnd = callSiteTableStart + callSiteTableLength;
    const uint8_t* p=callSiteTableStart;
    while (p < callSiteTableEnd) {
        uintptr_t start = readEncodedPointer(&p, callSiteEncoding);
        uintptr_t length = readEncodedPointer(&p, callSiteEncoding);
        uintptr_t landingPad = readEncodedPointer(&p, callSiteEncoding);
        readULEB128(&p); // action value not used for C code
        if ( landingPad == 0 )
            continue; // no landing pad for this entry
        if ( (start <= pcOffset) && (pcOffset < (start+length)) ) {
            // Found landing pad for the PC.
            // Set Instruction Pointer to so we re-enter function 
            // at landing pad. The landing pad is created by the compiler
            // to take two parameters in registers.
            _Unwind_SetGR(context, __builtin_eh_return_data_regno(0), 
                                                (uintptr_t)exceptionObject);
            _Unwind_SetGR(context, __builtin_eh_return_data_regno(1), 0);
            _Unwind_SetIP(context, funcStart+landingPad);
            return _URC_INSTALL_CONTEXT;
        }
    }
    
    // No landing pad found, continue unwinding.
    return _URC_CONTINUE_UNWIND;
}