libgo/runtime/go-caller.c

   1 /* go-caller.c -- look up function/file/line/entry info
   2
   3    Copyright 2009 The Go Authors. All rights reserved.
   4    Use of this source code is governed by a BSD-style
   5    license that can be found in the LICENSE file.  */
   6
   7 /* Implement runtime.Caller.  */
   8
   9 #include <stdint.h>
  10 #include <sys/types.h>
  11 #include <sys/stat.h>
  12 #include <unistd.h>
  13
  14 #include "backtrace.h"
  15
  16 #include "runtime.h"
  17
  18 /* Get the function name, file name, and line number for a PC value.
  19    We use the backtrace library to get this.  */
  20
  21 /* Data structure to gather file/line information.  */
  22
  23 struct caller
  24 {
  25   String fn;
  26   String file;
  27   intgo line;
  28   intgo index;
  29 };
  30
  31 /* Collect file/line information for a PC value.  If this is called
  32    more than once, due to inlined functions, we use the last call, as
  33    that is usually the most useful one.  */
  34
  35 static int
  36 callback (void *data, uintptr_t pc __attribute__ ((unused)),
  37           const char *filename, int lineno, const char *function)
  38 {
  39   struct caller *c = (struct caller *) data;
  40
  41   /* The libbacktrace library says that these strings might disappear,
  42      but with the current implementation they won't.  We can't easily
  43      allocate memory here, so for now assume that we can save a
  44      pointer to the strings.  */
  45   c->fn = runtime_gostringnocopy ((const byte *) function);
  46   c->file = runtime_gostringnocopy ((const byte *) filename);
  47   c->line = lineno;
  48
  49   if (c->index == 0)
  50     return 1;
  51
  52   if (c->index > 0)
  53     --c->index;
  54
  55   return 0;
  56 }
  57
  58 /* The error callback for backtrace_pcinfo and backtrace_syminfo.  */
  59
  60 static void
  61 error_callback (void *data __attribute__ ((unused)),
  62                 const char *msg, int errnum)
  63 {
  64   if (errnum == -1)
  65     return;
  66   if (errnum > 0)
  67     runtime_printf ("%s errno %d\n", msg, errnum);
  68   runtime_throw (msg);
  69 }
  70
  71 /* The backtrace library state.  */
  72
  73 static void *back_state;
  74
  75 /* A lock to control creating back_state.  */
  76
  77 static uint32 back_state_lock;
  78
  79 /* The program arguments.  */
  80
  81 extern Slice runtime_get_args(void);
  82
  83 /* Fetch back_state, creating it if necessary.  */
  84
  85 struct backtrace_state *
  86 __go_get_backtrace_state ()
  87 {
  88   uint32 set;
  89
  90   /* We may not have a g here, so we can't use runtime_lock.  */
  91   set = 0;
  92   while (!__atomic_compare_exchange_n (&back_state_lock, &set, 1, false, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED))
  93     {
  94       runtime_osyield ();
  95       set = 0;
  96     }
  97   if (back_state == NULL)
  98     {
  99       Slice args;
 100       const char *filename;
 101       struct stat s;
 102
 103       args = runtime_get_args();
 104       filename = NULL;
 105       if (args.__count > 0)
 106         filename = (const char*)((String*)args.__values)[0].str;
 107
 108       /* If there is no '/' in FILENAME, it was found on PATH, and
 109          might not be the same as the file with the same name in the
 110          current directory.  */
 111       if (filename != NULL && __builtin_strchr (filename, '/') == NULL)
 112         filename = NULL;
 113
 114       /* If the file is small, then it's not the real executable.
 115          This is specifically to deal with Docker, which uses a bogus
 116          argv[0] (http://gcc.gnu.org/PR61895).  It would be nice to
 117          have a better check for whether this file is the real
 118          executable.  */
 119       if (filename != NULL && (stat (filename, &s) < 0 || s.st_size < 1024))
 120         filename = NULL;
 121
 122       back_state = backtrace_create_state (filename, 1, error_callback, NULL);
 123     }
 124   __atomic_store_n (&back_state_lock, 0, __ATOMIC_RELEASE);
 125   return back_state;
 126 }
 127
 128 /* Return function/file/line information for PC.  The index parameter
 129    is the entry on the stack of inlined functions; -1 means the last
 130    one.  */
 131
 132 static _Bool
 133 __go_file_line (uintptr pc, int index, String *fn, String *file, intgo *line)
 134 {
 135   struct caller c;
 136   struct backtrace_state *state;
 137
 138   runtime_memclr (&c, sizeof c);
 139   c.index = index;
 140   state = __go_get_backtrace_state ();
 141   backtrace_pcinfo (state, pc, callback, error_callback, &c);
 142   *fn = c.fn;
 143   *file = c.file;
 144   *line = c.line;
 145
 146   // If backtrace_pcinfo didn't get the function name from the debug
 147   // info, try to get it from the symbol table.
 148   if (fn->len == 0)
 149     backtrace_syminfo (state, pc, __go_syminfo_fnname_callback,
 150                        error_callback, fn);
 151
 152   return c.file.len > 0;
 153 }
 154
 155 /* Collect symbol information.  */
 156
 157 static void
 158 syminfo_callback (void *data, uintptr_t pc __attribute__ ((unused)),
 159                   const char *symname __attribute__ ((unused)),
 160                   uintptr_t address, uintptr_t size __attribute__ ((unused)))
 161 {
 162   uintptr_t *pval = (uintptr_t *) data;
 163
 164   *pval = address;
 165 }
 166
 167 /* Set *VAL to the value of the symbol for PC.  */
 168
 169 static _Bool
 170 __go_symbol_value (uintptr pc, uintptr *val)
 171 {
 172   *val = 0;
 173   backtrace_syminfo (__go_get_backtrace_state (), pc, syminfo_callback,
 174                      error_callback, val);
 175   return *val != 0;
 176 }
 177
 178 /* The values returned by runtime.Caller.  */
 179
 180 struct caller_ret
 181 {
 182   uintptr_t pc;
 183   String file;
 184   intgo line;
 185   _Bool ok;
 186 };
 187
 188 struct caller_ret Caller (int n) __asm__ (GOSYM_PREFIX "runtime.Caller");
 189
 190 /* Implement runtime.Caller.  */
 191
 192 struct caller_ret
 193 Caller (int skip)
 194 {
 195   struct caller_ret ret;
 196   Location loc;
 197   int32 n;
 198
 199   runtime_memclr (&ret, sizeof ret);
 200   n = runtime_callers (skip + 1, &loc, 1, false);
 201   if (n < 1 || loc.pc == 0)
 202     return ret;
 203   ret.pc = loc.pc;
 204   ret.file = loc.filename;
 205   ret.line = loc.lineno;
 206   ret.ok = 1;
 207   return ret;
 208 }
 209
 210 /* Look up the function name, file name, and line number for a PC.  */
 211
 212 struct funcfileline_return
 213 {
 214   String retfn;
 215   String retfile;
 216   intgo retline;
 217 };
 218
 219 struct funcfileline_return
 220 runtime_funcfileline (uintptr targetpc, int32 index)
 221   __asm__ (GOSYM_PREFIX "runtime.funcfileline");
 222
 223 struct funcfileline_return
 224 runtime_funcfileline (uintptr targetpc, int32 index)
 225 {
 226   struct funcfileline_return ret;
 227
 228   if (!__go_file_line (targetpc, index, &ret.retfn, &ret.retfile,
 229                        &ret.retline))
 230     runtime_memclr (&ret, sizeof ret);
 231   return ret;
 232 }
 233
 234 /* Return the entry point of a function.  */
 235 uintptr runtime_funcentry(uintptr)
 236   __asm__ (GOSYM_PREFIX "runtime.funcentry");
 237
 238 uintptr
 239 runtime_funcentry (uintptr pc)
 240 {
 241   uintptr val;
 242
 243   if (!__go_symbol_value (pc, &val))
 244     return 0;
 245   return val;
 246 }