1/* ===-- gcc_personality_v0.c - Implement __gcc_personality_v0 -------------===
2 *
3 *      	       The LLVM Compiler Infrastructure
4 *
5 * This file is dual licensed under the MIT and the University of Illinois Open
6 * Source Licenses. See LICENSE.TXT for details.
7 *
8 * ===----------------------------------------------------------------------===
9 *
10 */
11
12#include "int_lib.h"
13
14#include <unwind.h>
15
16/*
17 * Pointer encodings documented at:
18 *   http://refspecs.freestandards.org/LSB_1.3.0/gLSB/gLSB/ehframehdr.html
19 */
20
21#define DW_EH_PE_omit      0xff  /* no data follows */
22
23#define DW_EH_PE_absptr    0x00
24#define DW_EH_PE_uleb128   0x01
25#define DW_EH_PE_udata2    0x02
26#define DW_EH_PE_udata4    0x03
27#define DW_EH_PE_udata8    0x04
28#define DW_EH_PE_sleb128   0x09
29#define DW_EH_PE_sdata2    0x0A
30#define DW_EH_PE_sdata4    0x0B
31#define DW_EH_PE_sdata8    0x0C
32
33#define DW_EH_PE_pcrel     0x10
34#define DW_EH_PE_textrel   0x20
35#define DW_EH_PE_datarel   0x30
36#define DW_EH_PE_funcrel   0x40
37#define DW_EH_PE_aligned   0x50
38#define DW_EH_PE_indirect  0x80 /* gcc extension */
39
40
41
42/* read a uleb128 encoded value and advance pointer */
43static uintptr_t readULEB128(const uint8_t** data)
44{
45    uintptr_t result = 0;
46    uintptr_t shift = 0;
47    unsigned char byte;
48    const uint8_t* p = *data;
49    do {
50        byte = *p++;
51        result |= (byte & 0x7f) << shift;
52        shift += 7;
53    } while (byte & 0x80);
54    *data = p;
55    return result;
56}
57
58/* read a pointer encoded value and advance pointer */
59static uintptr_t readEncodedPointer(const uint8_t** data, uint8_t encoding)
60{
61    const uint8_t* p = *data;
62    uintptr_t result = 0;
63
64    if ( encoding == DW_EH_PE_omit )
65        return 0;
66
67    /* first get value */
68    switch (encoding & 0x0F) {
69        case DW_EH_PE_absptr:
70            result = *((const uintptr_t*)p);
71            p += sizeof(uintptr_t);
72            break;
73        case DW_EH_PE_uleb128:
74            result = readULEB128(&p);
75            break;
76        case DW_EH_PE_udata2:
77            result = *((const uint16_t*)p);
78            p += sizeof(uint16_t);
79            break;
80        case DW_EH_PE_udata4:
81            result = *((const uint32_t*)p);
82            p += sizeof(uint32_t);
83            break;
84        case DW_EH_PE_udata8:
85            result = *((const uint64_t*)p);
86            p += sizeof(uint64_t);
87            break;
88        case DW_EH_PE_sdata2:
89            result = *((const int16_t*)p);
90            p += sizeof(int16_t);
91            break;
92        case DW_EH_PE_sdata4:
93            result = *((const int32_t*)p);
94            p += sizeof(int32_t);
95            break;
96        case DW_EH_PE_sdata8:
97            result = *((const int64_t*)p);
98            p += sizeof(int64_t);
99            break;
100        case DW_EH_PE_sleb128:
101        default:
102            /* not supported */
103            compilerrt_abort();
104            break;
105    }
106
107    /* then add relative offset */
108    switch ( encoding & 0x70 ) {
109        case DW_EH_PE_absptr:
110            /* do nothing */
111            break;
112        case DW_EH_PE_pcrel:
113            result += (uintptr_t)(*data);
114            break;
115        case DW_EH_PE_textrel:
116        case DW_EH_PE_datarel:
117        case DW_EH_PE_funcrel:
118        case DW_EH_PE_aligned:
119        default:
120            /* not supported */
121            compilerrt_abort();
122            break;
123    }
124
125    /* then apply indirection */
126    if (encoding & DW_EH_PE_indirect) {
127        result = *((const uintptr_t*)result);
128    }
129
130    *data = p;
131    return result;
132}
133
134
135/*
136 * The C compiler makes references to __gcc_personality_v0 in
137 * the dwarf unwind information for translation units that use
138 * __attribute__((cleanup(xx))) on local variables.
139 * This personality routine is called by the system unwinder
140 * on each frame as the stack is unwound during a C++ exception
141 * throw through a C function compiled with -fexceptions.
142 */
143#if __USING_SJLJ_EXCEPTIONS__
144/* the setjump-longjump based exceptions personality routine has a
145 * different name */
146COMPILER_RT_ABI _Unwind_Reason_Code
147__gcc_personality_sj0(int version, _Unwind_Action actions,
148         uint64_t exceptionClass, struct _Unwind_Exception* exceptionObject,
149         struct _Unwind_Context *context)
150#else
151COMPILER_RT_ABI _Unwind_Reason_Code
152__gcc_personality_v0(int version, _Unwind_Action actions,
153         uint64_t exceptionClass, struct _Unwind_Exception* exceptionObject,
154         struct _Unwind_Context *context)
155#endif
156{
157    /* Since C does not have catch clauses, there is nothing to do during */
158    /* phase 1 (the search phase). */
159    if ( actions & _UA_SEARCH_PHASE )
160        return _URC_CONTINUE_UNWIND;
161
162    /* There is nothing to do if there is no LSDA for this frame. */
163    const uint8_t* lsda = (uint8_t*)_Unwind_GetLanguageSpecificData(context);
164    if ( lsda == (uint8_t*) 0 )
165        return _URC_CONTINUE_UNWIND;
166
167    uintptr_t pc = _Unwind_GetIP(context)-1;
168    uintptr_t funcStart = _Unwind_GetRegionStart(context);
169    uintptr_t pcOffset = pc - funcStart;
170
171    /* Parse LSDA header. */
172    uint8_t lpStartEncoding = *lsda++;
173    if (lpStartEncoding != DW_EH_PE_omit) {
174        readEncodedPointer(&lsda, lpStartEncoding);
175    }
176    uint8_t ttypeEncoding = *lsda++;
177    if (ttypeEncoding != DW_EH_PE_omit) {
178        readULEB128(&lsda);
179    }
180    /* Walk call-site table looking for range that includes current PC. */
181    uint8_t         callSiteEncoding = *lsda++;
182    uint32_t        callSiteTableLength = readULEB128(&lsda);
183    const uint8_t*  callSiteTableStart = lsda;
184    const uint8_t*  callSiteTableEnd = callSiteTableStart + callSiteTableLength;
185    const uint8_t* p=callSiteTableStart;
186    while (p < callSiteTableEnd) {
187        uintptr_t start = readEncodedPointer(&p, callSiteEncoding);
188        uintptr_t length = readEncodedPointer(&p, callSiteEncoding);
189        uintptr_t landingPad = readEncodedPointer(&p, callSiteEncoding);
190        readULEB128(&p); /* action value not used for C code */
191        if ( landingPad == 0 )
192            continue; /* no landing pad for this entry */
193        if ( (start <= pcOffset) && (pcOffset < (start+length)) ) {
194            /* Found landing pad for the PC.
195             * Set Instruction Pointer to so we re-enter function
196             * at landing pad. The landing pad is created by the compiler
197             * to take two parameters in registers.
198             */
199            _Unwind_SetGR(context, __builtin_eh_return_data_regno(0),
200                          (uintptr_t)exceptionObject);
201            _Unwind_SetGR(context, __builtin_eh_return_data_regno(1), 0);
202            _Unwind_SetIP(context, (funcStart + landingPad));
203            return _URC_INSTALL_CONTEXT;
204        }
205    }
206
207    /* No landing pad found, continue unwinding. */
208    return _URC_CONTINUE_UNWIND;
209}
210
211