gdb/bpf-tdep.c

   1 /* Target-dependent code for BPF.
   2
   3    Copyright (C) 2020-2022 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 "defs.h"
  21 #include "arch-utils.h"
  22 #include "dis-asm.h"
  23 #include "frame.h"
  24 #include "frame-unwind.h"
  25 #include "trad-frame.h"
  26 #include "symtab.h"
  27 #include "value.h"
  28 #include "gdbcmd.h"
  29 #include "breakpoint.h"
  30 #include "inferior.h"
  31 #include "regcache.h"
  32 #include "target.h"
  33 #include "dwarf2/frame.h"
  34 #include "osabi.h"
  35 #include "target-descriptions.h"
  36 #include "remote.h"
  37 #include "gdbarch.h"
  38
  39 \f
  40 /* eBPF registers.  */
  41
  42 enum bpf_regnum
  43 {
  44   BPF_R0_REGNUM,                /* return value */
  45   BPF_R1_REGNUM,
  46   BPF_R2_REGNUM,
  47   BPF_R3_REGNUM,
  48   BPF_R4_REGNUM,
  49   BPF_R5_REGNUM,
  50   BPF_R6_REGNUM,
  51   BPF_R7_REGNUM,
  52   BPF_R8_REGNUM,
  53   BPF_R9_REGNUM,
  54   BPF_R10_REGNUM,               /* sp */
  55   BPF_PC_REGNUM,
  56 };
  57
  58 #define BPF_NUM_REGS    (BPF_PC_REGNUM + 1)
  59
  60 /* Target-dependent structure in gdbarch.  */
  61 struct bpf_gdbarch_tdep : gdbarch_tdep_base
  62 {
  63 };
  64
  65 \f
  66 /* Internal debugging facilities.  */
  67
  68 /* When this is set to non-zero debugging information will be
  69    printed.  */
  70
  71 static unsigned int bpf_debug_flag = 0;
  72
  73 /* The show callback for 'show debug bpf'.  */
  74
  75 static void
  76 show_bpf_debug (struct ui_file *file, int from_tty,
  77                 struct cmd_list_element *c, const char *value)
  78 {
  79   gdb_printf (file, _("Debugging of BPF is %s.\n"), value);
  80 }
  81
  82 \f
  83 /* BPF registers.  */
  84
  85 static const char *bpf_register_names[] =
  86 {
  87   "r0",   "r1",  "r2",    "r3",   "r4",   "r5",   "r6",   "r7",
  88   "r8",   "r9",  "r10",   "pc"
  89 };
  90
  91 /* Return the name of register REGNUM.  */
  92
  93 static const char *
  94 bpf_register_name (struct gdbarch *gdbarch, int reg)
  95 {
  96   if (reg >= 0 && reg < BPF_NUM_REGS)
  97     return bpf_register_names[reg];
  98   return NULL;
  99 }
 100
 101 /* Return the GDB type of register REGNUM.  */
 102
 103 static struct type *
 104 bpf_register_type (struct gdbarch *gdbarch, int reg)
 105 {
 106   if (reg == BPF_R10_REGNUM)
 107     return builtin_type (gdbarch)->builtin_data_ptr;
 108   else if (reg == BPF_PC_REGNUM)
 109     return builtin_type (gdbarch)->builtin_func_ptr;
 110   return builtin_type (gdbarch)->builtin_int64;
 111 }
 112
 113 /* Return the GDB register number corresponding to DWARF's REG.  */
 114
 115 static int
 116 bpf_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int reg)
 117 {
 118   if (reg >= 0 && reg < BPF_NUM_REGS)
 119     return reg;
 120   return -1;
 121 }
 122
 123 /* Implement the "print_insn" gdbarch method.  */
 124
 125 static int
 126 bpf_gdb_print_insn (bfd_vma memaddr, disassemble_info *info)
 127 {
 128   info->symbols = NULL;
 129   return default_print_insn (memaddr, info);
 130 }
 131
 132 \f
 133 /* Return PC of first real instruction of the function starting at
 134    START_PC.  */
 135
 136 static CORE_ADDR
 137 bpf_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR start_pc)
 138 {
 139   gdb_printf (gdb_stdlog,
 140               "Skipping prologue: start_pc=%s\n",
 141               paddress (gdbarch, start_pc));
 142   /* XXX: to be completed.  */
 143   return start_pc + 0;
 144 }
 145
 146 \f
 147 /* Frame unwinder.
 148
 149    XXX it is not clear how to unwind in eBPF, since the stack is not
 150    guaranteed to be contiguous, and therefore no relative stack
 151    addressing can be done in the callee in order to access the
 152    caller's stack frame.  To explore with xBPF, which will relax this
 153    restriction.  */
 154
 155 /* Given THIS_FRAME, return its ID.  */
 156
 157 static void
 158 bpf_frame_this_id (struct frame_info *this_frame,
 159                    void **this_prologue_cache,
 160                    struct frame_id *this_id)
 161 {
 162   /* Note that THIS_ID defaults to the outermost frame if we don't set
 163      anything here.  See frame.c:compute_frame_id.  */
 164 }
 165
 166 /* Return the reason why we can't unwind past THIS_FRAME.  */
 167
 168 static enum unwind_stop_reason
 169 bpf_frame_unwind_stop_reason (struct frame_info *this_frame,
 170                               void **this_cache)
 171 {
 172   return UNWIND_OUTERMOST;
 173 }
 174
 175 /* Ask THIS_FRAME to unwind its register.  */
 176
 177 static struct value *
 178 bpf_frame_prev_register (struct frame_info *this_frame,
 179                          void **this_prologue_cache, int regnum)
 180 {
 181   return frame_unwind_got_register (this_frame, regnum, regnum);
 182 }
 183
 184 /* Frame unwinder machinery for BPF.  */
 185
 186 static const struct frame_unwind bpf_frame_unwind =
 187 {
 188   "bpf prologue",
 189   NORMAL_FRAME,
 190   bpf_frame_unwind_stop_reason,
 191   bpf_frame_this_id,
 192   bpf_frame_prev_register,
 193   NULL,
 194   default_frame_sniffer
 195 };
 196
 197 \f
 198 /* Breakpoints.  */
 199
 200 /* Enum describing the different kinds of breakpoints.  We currently
 201    just support one, implemented by the brkpt xbpf instruction.   */
 202
 203 enum bpf_breakpoint_kinds
 204 {
 205   BPF_BP_KIND_BRKPT = 0,
 206 };
 207
 208 /* Implement the breakpoint_kind_from_pc gdbarch method.  */
 209
 210 static int
 211 bpf_breakpoint_kind_from_pc (struct gdbarch *gdbarch, CORE_ADDR *start_pc)
 212 {
 213   /* We support just one kind of breakpoint.  */
 214   return BPF_BP_KIND_BRKPT;
 215 }
 216
 217 /* Implement the sw_breakpoint_from_kind gdbarch method.  */
 218
 219 static const gdb_byte *
 220 bpf_sw_breakpoint_from_kind (struct gdbarch *gdbarch, int kind, int *size)
 221 {
 222   static unsigned char brkpt_insn[]
 223     = {0x8c, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
 224
 225   switch (kind)
 226     {
 227     case BPF_BP_KIND_BRKPT:
 228       *size = 8;
 229       return brkpt_insn;
 230     default:
 231       gdb_assert_not_reached ("unexpected BPF breakpoint kind");
 232     }
 233 }
 234
 235 \f
 236 /* Assuming THIS_FRAME is a dummy frame, return its frame ID.  */
 237
 238 static struct frame_id
 239 bpf_dummy_id (struct gdbarch *gdbarch, struct frame_info *this_frame)
 240 {
 241   CORE_ADDR sp = get_frame_register_unsigned (this_frame,
 242                                               gdbarch_sp_regnum (gdbarch));
 243   return frame_id_build (sp, get_frame_pc (this_frame));
 244 }
 245
 246 /* Implement the push dummy call gdbarch callback.  */
 247
 248 static CORE_ADDR
 249 bpf_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
 250                      struct regcache *regcache, CORE_ADDR bp_addr,
 251                      int nargs, struct value **args, CORE_ADDR sp,
 252                      function_call_return_method return_method,
 253                      CORE_ADDR struct_addr)
 254 {
 255   gdb_printf (gdb_stdlog, "Pushing dummy call: sp=%s\n",
 256               paddress (gdbarch, sp));
 257   /* XXX writeme  */
 258   return sp;
 259 }
 260
 261 /* Extract a function return value of TYPE from REGCACHE,
 262    and copy it into VALBUF.  */
 263
 264 static void
 265 bpf_extract_return_value (struct type *type, struct regcache *regcache,
 266                           gdb_byte *valbuf)
 267 {
 268   int len = TYPE_LENGTH (type);
 269   gdb_byte vbuf[8];
 270
 271   gdb_assert (len <= 8);
 272   regcache->cooked_read (BPF_R0_REGNUM, vbuf);
 273   memcpy (valbuf, vbuf + 8 - len, len);
 274 }
 275
 276 /* Store the function return value of type TYPE from VALBUF into REGNAME.  */
 277
 278 static void
 279 bpf_store_return_value (struct type *type, struct regcache *regcache,
 280                         const gdb_byte *valbuf)
 281 {
 282   int len = TYPE_LENGTH (type);
 283   gdb_byte vbuf[8];
 284
 285   gdb_assert (len <= 8);
 286   memset (vbuf, 0, sizeof (vbuf));
 287   memcpy (vbuf + 8 - len, valbuf, len);
 288   regcache->cooked_write (BPF_R0_REGNUM, vbuf);
 289 }
 290
 291 /* Handle function's return value.  */
 292
 293 static enum return_value_convention
 294 bpf_return_value (struct gdbarch *gdbarch, struct value *function,
 295                   struct type *type, struct regcache *regcache,
 296                   gdb_byte *readbuf, const gdb_byte *writebuf)
 297 {
 298   int len = TYPE_LENGTH (type);
 299
 300   if (len > 8)
 301     return RETURN_VALUE_STRUCT_CONVENTION;
 302
 303   if (readbuf != NULL)
 304     bpf_extract_return_value (type, regcache, readbuf);
 305   if (writebuf != NULL)
 306     bpf_store_return_value (type, regcache, writebuf);
 307
 308   return RETURN_VALUE_REGISTER_CONVENTION;
 309 }
 310
 311 \f
 312 /* Initialize the current architecture based on INFO.  If possible, re-use an
 313    architecture from ARCHES, which is a list of architectures already created
 314    during this debugging session.  */
 315
 316 static struct gdbarch *
 317 bpf_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
 318 {
 319   /* If there is already a candidate, use it.  */
 320   arches = gdbarch_list_lookup_by_info (arches, &info);
 321   if (arches != NULL)
 322     return arches->gdbarch;
 323
 324   /* Allocate space for the new architecture.  */
 325   bpf_gdbarch_tdep *tdep = new bpf_gdbarch_tdep;
 326   struct gdbarch *gdbarch = gdbarch_alloc (&info, tdep);
 327
 328   /* Information about registers, etc.  */
 329   set_gdbarch_num_regs (gdbarch, BPF_NUM_REGS);
 330   set_gdbarch_register_name (gdbarch, bpf_register_name);
 331   set_gdbarch_register_type (gdbarch, bpf_register_type);
 332
 333   /* Register numbers of various important registers.  */
 334   set_gdbarch_sp_regnum (gdbarch, BPF_R10_REGNUM);
 335   set_gdbarch_pc_regnum (gdbarch, BPF_PC_REGNUM);
 336
 337   /* Map DWARF2 registers to GDB registers.  */
 338   set_gdbarch_dwarf2_reg_to_regnum (gdbarch, bpf_dwarf2_reg_to_regnum);
 339
 340   /* Call dummy code.  */
 341   set_gdbarch_call_dummy_location (gdbarch, ON_STACK);
 342   set_gdbarch_dummy_id (gdbarch, bpf_dummy_id);
 343   set_gdbarch_push_dummy_call (gdbarch, bpf_push_dummy_call);
 344
 345   /* Returning results.  */
 346   set_gdbarch_return_value (gdbarch, bpf_return_value);
 347
 348   /* Advance PC across function entry code.  */
 349   set_gdbarch_skip_prologue (gdbarch, bpf_skip_prologue);
 350
 351   /* Stack grows downward.  */
 352   set_gdbarch_inner_than (gdbarch, core_addr_lessthan);
 353
 354   /* Breakpoint manipulation.  */
 355   set_gdbarch_breakpoint_kind_from_pc (gdbarch, bpf_breakpoint_kind_from_pc);
 356   set_gdbarch_sw_breakpoint_from_kind (gdbarch, bpf_sw_breakpoint_from_kind);
 357
 358   /* Frame handling.  */
 359   set_gdbarch_frame_args_skip (gdbarch, 8);
 360
 361   /* Disassembly.  */
 362   set_gdbarch_print_insn (gdbarch, bpf_gdb_print_insn);
 363
 364   /* Hook in ABI-specific overrides, if they have been registered.  */
 365   gdbarch_init_osabi (info, gdbarch);
 366
 367   /* Install unwinders.  */
 368   frame_unwind_append_unwinder (gdbarch, &bpf_frame_unwind);
 369
 370   return gdbarch;
 371 }
 372
 373 void _initialize_bpf_tdep ();
 374 void
 375 _initialize_bpf_tdep ()
 376 {
 377   register_gdbarch_init (bfd_arch_bpf, bpf_gdbarch_init);
 378
 379   /* Add commands 'set/show debug bpf'.  */
 380   add_setshow_zuinteger_cmd ("bpf", class_maintenance,
 381                              &bpf_debug_flag,
 382                              _("Set BPF debugging."),
 383                              _("Show BPF debugging."),
 384                              _("Enables BPF specific debugging output."),
 385                              NULL,
 386                              &show_bpf_debug,
 387                              &setdebuglist, &showdebuglist);
 388 }