libgo/runtime/go-fieldtrack.c

   1 /* go-fieldtrack.c -- structure field data analysis.
   2
   3    Copyright 2012 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 #include "runtime.h"
   8
   9 /* The compiler will track fields that have the tag go:"track".  Any
  10    function that refers to such a field will call this function with a
  11    string
  12        fieldtrack "package.type.field"
  13
  14    This function does not actually do anything.  Instead, we gather
  15    the field tracking information by looking for strings of that form
  16    in the read-only data section.  This is, of course, a horrible
  17    hack, but it's good enough for now.  We can improve it, e.g., by a
  18    linker plugin, if this turns out to be useful.  */
  19
  20 void
  21 __go_fieldtrack (byte *p __attribute__ ((unused)))
  22 {
  23 }
  24
  25 /* A runtime function to add all the tracked fields to a
  26    map[string]bool.  */
  27
  28 extern void *mapassign (const struct maptype *, void *hmap, const void *key)
  29   __asm__ (GOSYM_PREFIX "runtime.mapassign");
  30
  31 // The type descriptor for map[string] bool.  */
  32 extern const char map_string_bool[] __attribute__ ((weak));
  33 extern const char map_string_bool[]
  34   __asm__ (GOSYM_PREFIX "type..map_6string_7bool");
  35
  36 void runtime_Fieldtrack (void *) __asm__ (GOSYM_PREFIX "runtime.Fieldtrack");
  37
  38 void
  39 runtime_Fieldtrack (void *m)
  40 {
  41   const char *p;
  42   const char *pend;
  43   const char *prefix;
  44   size_t prefix_len;
  45
  46   if (map_string_bool == NULL)
  47     return;
  48
  49   p = __data_start;
  50   if (p == NULL)
  51     p = __etext;
  52   if (p == NULL)
  53     p = _etext;
  54   if (p == NULL)
  55     return;
  56
  57   pend = __edata;
  58   if (pend == NULL)
  59     pend = _edata;
  60   if (pend == NULL)
  61     pend = __bss_start;
  62   if (pend == NULL)
  63     return;
  64
  65   prefix = "fieldtrack ";
  66   prefix_len = __builtin_strlen (prefix);
  67
  68   while (p < pend)
  69     {
  70       const char *q1;
  71       const char *q2;
  72
  73       q1 = __builtin_memchr (p + prefix_len, '"', pend - (p + prefix_len));
  74       if (q1 == NULL)
  75         break;
  76
  77       if (__builtin_memcmp (q1 - prefix_len, prefix, prefix_len) != 0)
  78         {
  79           p = q1 + 1;
  80           continue;
  81         }
  82
  83       q1++;
  84       q2 = __builtin_memchr (q1, '"', pend - q1);
  85       if (q2 == NULL)
  86         break;
  87
  88       if (__builtin_memchr (q1, '\0', q2 - q1) == NULL)
  89         {
  90           String s;
  91           void *p;
  92
  93           s.str = (const byte *) q1;
  94           s.len = q2 - q1;
  95           p = mapassign((const void*) map_string_bool, m, &s);
  96           *(_Bool*)p = 1;
  97         }
  98
  99       p = q2;
 100     }
 101 }