1 // backtrace.h - Fallback backtrace implementation. i386 implementation.
2
3 /* Copyright (C) 2005, 2006 Free Software Foundation
4
5 This file is part of libgcj.
6
7 This software is copyrighted work licensed under the terms of the
8 Libgcj License. Please consult the file "LIBGCJ_LICENSE" for
9 details. */
10
11 #ifndef __SYSDEP_BACKTRACE_H__
12 #define __SYSDEP_BACKTRACE_H__
13
14 #include <java-stack.h>
15
16 #ifdef __CYGWIN__
17 /* To allow this to link as a DLL. */
18 #define MAIN_FUNC dll_crt0__FP11per_process
19 extern "C" int MAIN_FUNC () __declspec(dllimport);
20 #elif defined (_WIN32)
21 #define MAIN_FUNC DllMain
22 extern "C" int __stdcall MAIN_FUNC (void *, unsigned long, void *);
23 #else /* !__CYGWIN__ && !_WIN32 */
24 #define MAIN_FUNC main
25 extern int MAIN_FUNC (int, char **);
26 #endif /* ?__CYGWIN__ */
27
28 /* The context used to keep track of our position while unwinding through
29 the call stack. */
30 struct _Unwind_Context
31 {
32 /* The starting address of the method. */
33 _Jv_uintptr_t meth_addr;
34
35 /* The return address in the method. */
36 _Jv_uintptr_t ret_addr;
37 };
38
39 #ifdef __USING_SJLJ_EXCEPTIONS__
40
41 #undef _Unwind_GetIPInfo
42 #define _Unwind_GetIPInfo(ctx,ip_before_insn) \
43 (*(ip_before_insn) = 1, (ctx)->ret_addr)
44
45 #undef _Unwind_GetRegionStart
46 #define _Unwind_GetRegionStart(ctx) \
47 ((ctx)->meth_addr)
48
49 #undef _Unwind_Backtrace
50 #define _Unwind_Backtrace(trace_fn,state_ptr) \
51 (fallback_backtrace (trace_fn, state_ptr))
52
53 #endif /* __USING_SJLJ_EXCEPTIONS__ */
54
55 /* Unwind through the call stack calling TRACE_FN with STATE for each stack
56 frame. Returns the reason why the unwinding was stopped. */
57 _Unwind_Reason_Code
fallback_backtrace(_Unwind_Trace_Fn trace_fn,_Jv_UnwindState * state)58 fallback_backtrace (_Unwind_Trace_Fn trace_fn, _Jv_UnwindState *state)
59 {
60 register _Jv_uintptr_t *_ebp __asm__ ("ebp");
61 register _Jv_uintptr_t _esp __asm__ ("esp");
62 _Jv_uintptr_t rfp;
63 _Unwind_Context ctx;
64
65 for (rfp = *_ebp; rfp; rfp = *(_Jv_uintptr_t *)rfp)
66 {
67 /* Sanity checks to eliminate dubious-looking frame pointer chains.
68 The frame pointer should be a 32-bit word-aligned stack address.
69 Since the stack grows downwards on x86, the frame pointer must have
70 a value greater than the current value of the stack pointer, it
71 should not be below the supposed next frame pointer and it should
72 not be too far off from the supposed next frame pointer. */
73 int diff = *(_Jv_uintptr_t *)rfp - rfp;
74 if ((rfp & 0x00000003) != 0 || rfp < _esp
75 || diff > 4 * 1024 || diff < 0)
76 break;
77
78 /* Get the return address in the calling function. This is stored on
79 the stack just before the value of the old frame pointer. */
80 ctx.ret_addr = *(_Jv_uintptr_t *)(rfp + sizeof (_Jv_uintptr_t));
81
82 /* Try to locate a "pushl %ebp; movl %esp, %ebp" function prologue
83 by scanning backwards at even addresses below the return address.
84 This instruction sequence is encoded either as 0x55 0x89 0xE5 or as
85 0x55 0x8B 0xEC. We give up if we do not find this sequence even
86 after scanning 1024K of memory.
87 FIXME: This is not robust and will probably give us false positives,
88 but this is about the best we can do if we do not have DWARF-2 unwind
89 information based exception handling. */
90 ctx.meth_addr = (_Jv_uintptr_t)NULL;
91 _Jv_uintptr_t scan_addr = (ctx.ret_addr & 0xFFFFFFFE) - 2;
92 _Jv_uintptr_t limit_addr
93 = (scan_addr > 1024 * 1024) ? (scan_addr - 1024 * 1024) : 2;
94 for ( ; scan_addr >= limit_addr; scan_addr -= 2)
95 {
96 unsigned char *scan_bytes = (unsigned char *)scan_addr;
97 if (scan_bytes[0] == 0x55
98 && ((scan_bytes[1] == 0x89 && scan_bytes[2] == 0xE5)
99 || (scan_bytes[1] == 0x8B && scan_bytes[2] == 0xEC)))
100 {
101 ctx.meth_addr = scan_addr;
102 break;
103 }
104 }
105
106 /* Now call the unwinder callback function. */
107 if (trace_fn != NULL)
108 (*trace_fn) (&ctx, state);
109
110 /* No need to unwind beyond _Jv_RunMain(), _Jv_ThreadStart or
111 main(). */
112 void *jv_runmain
113 = (void *)(void (*)(JvVMInitArgs *, jclass, const char *, int,
114 const char **, bool))_Jv_RunMain;
115 if (ctx.meth_addr == (_Jv_uintptr_t)jv_runmain
116 || ctx.meth_addr == (_Jv_uintptr_t)_Jv_ThreadStart
117 || (ctx.meth_addr - (_Jv_uintptr_t)MAIN_FUNC) < 16)
118 break;
119 }
120
121 return _URC_NO_REASON;
122 }
123 #endif
124