llvm-project/compiler-rt/lib/builtins/gcc_personality_v0.c

/* ===-- gcc_personality_v0.c - Implement __gcc_personality_v0 -------------===
 *
 *      	       The LLVM Compiler Infrastructure
 *
 * This file is dual licensed under the MIT and the University of Illinois Open
 * Source Licenses. See LICENSE.TXT for details.
 *
 * ===----------------------------------------------------------------------===
 *
 */

#include "int_lib.h"

#include <unwind.h>

/*
 * 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 = *((const uintptr_t*)p);
            p += sizeof(uintptr_t);
            break;
        case DW_EH_PE_uleb128:
            result = readULEB128(&p);
            break;
        case DW_EH_PE_udata2:
            result = *((const uint16_t*)p);
            p += sizeof(uint16_t);
            break;
        case DW_EH_PE_udata4:
            result = *((const uint32_t*)p);
            p += sizeof(uint32_t);
            break;
        case DW_EH_PE_udata8:
            result = *((const uint64_t*)p);
            p += sizeof(uint64_t);
            break;
        case DW_EH_PE_sdata2:
            result = *((const int16_t*)p);
            p += sizeof(int16_t);
            break;
        case DW_EH_PE_sdata4:
            result = *((const int32_t*)p);
            p += sizeof(int32_t);
            break;
        case DW_EH_PE_sdata8:
            result = *((const int64_t*)p);
            p += sizeof(int64_t);
            break;
        case DW_EH_PE_sleb128:
        default:
            /* not supported */
            compilerrt_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 */
            compilerrt_abort();
            break;
    }

    /* then apply indirection */
    if (encoding & DW_EH_PE_indirect) {
        result = *((const 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.
 */
#if __USING_SJLJ_EXCEPTIONS__
/* the setjump-longjump based exceptions personality routine has a
 * different name */
COMPILER_RT_ABI _Unwind_Reason_Code
__gcc_personality_sj0(int version, _Unwind_Action actions,
         uint64_t exceptionClass, struct _Unwind_Exception* exceptionObject,
         struct _Unwind_Context *context)
#else
COMPILER_RT_ABI _Unwind_Reason_Code
__gcc_personality_v0(int version, _Unwind_Action actions,
         uint64_t exceptionClass, struct _Unwind_Exception* exceptionObject,
         struct _Unwind_Context *context)
#endif
{
    /* 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 = (uint8_t*)_Unwind_GetLanguageSpecificData(context);
    if ( lsda == (uint8_t*) 0 )
        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;
}