gdb/arch/x86-linux-tdesc-features.c

   1 /* Target description related code for GNU/Linux x86 (i386 and x86-64).
   2
   3    Copyright (C) 2024 Free Software Foundation, Inc.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20 #include "arch/x86-linux-tdesc-features.h"
  21
  22 /* A structure used to describe a single xstate feature bit that might, or
  23    might not, be checked for when creating a target description for one of
  24    i386, amd64, or x32.
  25
  26    The different CPU/ABI types check for different xstate features when
  27    creating a target description.
  28
  29    We want to cache target descriptions, and this is currently done in
  30    three separate caches, one each for i386, amd64, and x32.  Additionally,
  31    the caching we're discussing here is Linux only, and for Linux, the only
  32    thing that has an impact on target description creation is the xcr0
  33    value.
  34
  35    In order to ensure the cache functions correctly we need to filter out
  36    only those xcr0 feature bits that are relevant, we can then cache target
  37    descriptions based on the relevant feature bits.  Two xcr0 values might
  38    be different, but have the same relevant feature bits.  In this case we
  39    would expect the two xcr0 values to map to the same cache entry.  */
  40
  41 struct x86_xstate_feature {
  42   /* The xstate feature mask.  This is a mask against an xcr0 value.  */
  43   uint64_t feature;
  44
  45   /* Is this feature checked when creating an i386 target description.  */
  46   bool is_i386;
  47
  48   /* Is this feature checked when creating an amd64 target description.  */
  49   bool is_amd64;
  50
  51   /* Is this feature checked when creating an x32 target description.  */
  52   bool is_x32;
  53 };
  54
  55 /* A constant table that describes all of the xstate features that are
  56    checked when building a target description for i386, amd64, or x32.
  57
  58    If in the future, due to simplifications or refactoring, this table ever
  59    ends up with 'true' for every xcr0 feature on every target type, then this
  60    is an indication that this table should probably be removed, and that the
  61    rest of the code in this file can be simplified.  */
  62
  63 static constexpr x86_xstate_feature x86_linux_all_xstate_features[] = {
  64   /* Feature,           i386,   amd64,  x32.  */
  65   { X86_XSTATE_PKRU,    true,   true,   true },
  66   { X86_XSTATE_AVX512,  true,   true,   true },
  67   { X86_XSTATE_AVX,     true,   true,   true },
  68   { X86_XSTATE_SSE,     true,   false,  false },
  69   { X86_XSTATE_X87,     true,   false,  false }
  70 };
  71
  72 /* Return a compile time constant which is a mask of all the xstate features
  73    that are checked for when building an i386 target description.  */
  74
  75 static constexpr uint64_t
  76 x86_linux_i386_xcr0_feature_mask_1 ()
  77 {
  78   uint64_t mask = 0;
  79
  80   for (const auto &entry : x86_linux_all_xstate_features)
  81     if (entry.is_i386)
  82       mask |= entry.feature;
  83
  84   return mask;
  85 }
  86
  87 /* Return a compile time constant which is a mask of all the xstate features
  88    that are checked for when building an amd64 target description.  */
  89
  90 static constexpr uint64_t
  91 x86_linux_amd64_xcr0_feature_mask_1 ()
  92 {
  93   uint64_t mask = 0;
  94
  95   for (const auto &entry : x86_linux_all_xstate_features)
  96     if (entry.is_amd64)
  97       mask |= entry.feature;
  98
  99   return mask;
 100 }
 101
 102 /* Return a compile time constant which is a mask of all the xstate features
 103    that are checked for when building an x32 target description.  */
 104
 105 static constexpr uint64_t
 106 x86_linux_x32_xcr0_feature_mask_1 ()
 107 {
 108   uint64_t mask = 0;
 109
 110   for (const auto &entry : x86_linux_all_xstate_features)
 111     if (entry.is_x32)
 112       mask |= entry.feature;
 113
 114   return mask;
 115 }
 116
 117 /* See arch/x86-linux-tdesc-features.h.  */
 118
 119 uint64_t
 120 x86_linux_i386_xcr0_feature_mask ()
 121 {
 122   return x86_linux_i386_xcr0_feature_mask_1 ();
 123 }
 124
 125 /* See arch/x86-linux-tdesc-features.h.  */
 126
 127 uint64_t
 128 x86_linux_amd64_xcr0_feature_mask ()
 129 {
 130   return x86_linux_amd64_xcr0_feature_mask_1 ();
 131 }
 132
 133 /* See arch/x86-linux-tdesc-features.h.  */
 134
 135 uint64_t
 136 x86_linux_x32_xcr0_feature_mask ()
 137 {
 138   return x86_linux_x32_xcr0_feature_mask_1 ();
 139 }
 140
 141 #ifdef GDBSERVER
 142
 143 /* See arch/x86-linux-tdesc-features.h.  */
 144
 145 int
 146 x86_linux_xcr0_to_tdesc_idx (uint64_t xcr0)
 147 {
 148   /* The following table shows which features are checked for when creating
 149      the target descriptions (see nat/x86-linux-tdesc.c), the feature order
 150      represents the bit order within the generated index number.
 151
 152      i386  | x87 sse avx avx512 pkru
 153      amd64 |         avx avx512 pkru
 154      i32   |         avx avx512 pkru
 155
 156      The features are ordered so that for each mode (i386, amd64, i32) the
 157      generated index will form a continuous range.  */
 158
 159   int idx = 0;
 160
 161   for (int i = 0; i < ARRAY_SIZE (x86_linux_all_xstate_features); ++i)
 162     {
 163       if ((xcr0 & x86_linux_all_xstate_features[i].feature)
 164           == x86_linux_all_xstate_features[i].feature)
 165         idx |= (1 << i);
 166     }
 167
 168   return idx;
 169 }
 170
 171 #endif /* GDBSERVER */
 172
 173 #ifdef IN_PROCESS_AGENT
 174
 175 /* Return a compile time constant which is a count of the number of xstate
 176    features that are checked for when building an i386 target description.  */
 177
 178 static constexpr int
 179 x86_linux_i386_tdesc_count_1 ()
 180 {
 181   uint64_t count = 0;
 182
 183   for (const auto &entry : x86_linux_all_xstate_features)
 184     if (entry.is_i386)
 185       ++count;
 186
 187   gdb_assert (count > 0);
 188
 189   return (1 << count);
 190 }
 191
 192 /* Return a compile time constant which is a count of the number of xstate
 193    features that are checked for when building an amd64 target description.  */
 194
 195 static constexpr int
 196 x86_linux_amd64_tdesc_count_1 ()
 197 {
 198   uint64_t count = 0;
 199
 200   for (const auto &entry : x86_linux_all_xstate_features)
 201     if (entry.is_amd64)
 202       ++count;
 203
 204   gdb_assert (count > 0);
 205
 206   return (1 << count);
 207 }
 208
 209 /* Return a compile time constant which is a count of the number of xstate
 210    features that are checked for when building an x32 target description.  */
 211
 212 static constexpr int
 213 x86_linux_x32_tdesc_count_1 ()
 214 {
 215   uint64_t count = 0;
 216
 217   for (const auto &entry : x86_linux_all_xstate_features)
 218     if (entry.is_x32)
 219       ++count;
 220
 221   gdb_assert (count > 0);
 222
 223   return (1 << count);
 224 }
 225
 226 /* See arch/x86-linux-tdesc-features.h.  */
 227
 228 int
 229 x86_linux_amd64_tdesc_count ()
 230 {
 231   return x86_linux_amd64_tdesc_count_1 ();
 232 }
 233
 234 /* See arch/x86-linux-tdesc-features.h.  */
 235
 236 int
 237 x86_linux_x32_tdesc_count ()
 238 {
 239   return x86_linux_x32_tdesc_count_1 ();
 240 }
 241
 242 /* See arch/x86-linux-tdesc-features.h.  */
 243
 244 int
 245 x86_linux_i386_tdesc_count ()
 246 {
 247   return x86_linux_i386_tdesc_count_1 ();
 248 }
 249
 250 /* See arch/x86-linux-tdesc-features.h.  */
 251
 252 uint64_t
 253 x86_linux_tdesc_idx_to_xcr0 (int idx)
 254 {
 255   uint64_t xcr0 = 0;
 256
 257   for (int i = 0; i < ARRAY_SIZE (x86_linux_all_xstate_features); ++i)
 258     {
 259       if ((idx & (1 << i)) != 0)
 260         xcr0 |= x86_linux_all_xstate_features[i].feature;
 261     }
 262
 263   return xcr0;
 264 }
 265
 266 #endif /* IN_PROCESS_AGENT */