gdb/bpf-tdep.c

   1 /* Target-dependent code for BPF.
   2
   3    Copyright (C) 2020-2023 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   gdb_static_assert (ARRAY_SIZE (bpf_register_names) == BPF_NUM_REGS);
  97   return bpf_register_names[reg];
  98 }
  99
 100 /* Return the GDB type of register REGNUM.  */
 101
 102 static struct type *
 103 bpf_register_type (struct gdbarch *gdbarch, int reg)
 104 {
 105   if (reg == BPF_R10_REGNUM)
 106     return builtin_type (gdbarch)->builtin_data_ptr;
 107   else if (reg == BPF_PC_REGNUM)
 108     return builtin_type (gdbarch)->builtin_func_ptr;
 109   return builtin_type (gdbarch)->builtin_int64;
 110 }
 111
 112 /* Return the GDB register number corresponding to DWARF's REG.  */
 113
 114 static int
 115 bpf_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int reg)
 116 {
 117   if (reg >= 0 && reg < BPF_NUM_REGS)
 118     return reg;
 119   return -1;
 120 }
 121
 122 /* Implement the "print_insn" gdbarch method.  */
 123
 124 static int
 125 bpf_gdb_print_insn (bfd_vma memaddr, disassemble_info *info)
 126 {
 127   info->symbols = NULL;
 128   return default_print_insn (memaddr, info);
 129 }
 130
 131 \f
 132 /* Return PC of first real instruction of the function starting at
 133    START_PC.  */
 134
 135 static CORE_ADDR
 136 bpf_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR start_pc)
 137 {
 138   gdb_printf (gdb_stdlog,
 139               "Skipping prologue: start_pc=%s\n",
 140               paddress (gdbarch, start_pc));
 141   /* XXX: to be completed.  */
 142   return start_pc + 0;
 143 }
 144
 145 \f
 146 /* Frame unwinder.
 147
 148    XXX it is not clear how to unwind in eBPF, since the stack is not
 149    guaranteed to be contiguous, and therefore no relative stack
 150    addressing can be done in the callee in order to access the
 151    caller's stack frame.  To explore with xBPF, which will relax this
 152    restriction.  */
 153
 154 /* Given THIS_FRAME, return its ID.  */
 155
 156 static void
 157 bpf_frame_this_id (frame_info_ptr this_frame,
 158                    void **this_prologue_cache,
 159                    struct frame_id *this_id)
 160 {
 161   /* Note that THIS_ID defaults to the outermost frame if we don't set
 162      anything here.  See frame.c:compute_frame_id.  */
 163 }
 164
 165 /* Return the reason why we can't unwind past THIS_FRAME.  */
 166
 167 static enum unwind_stop_reason
 168 bpf_frame_unwind_stop_reason (frame_info_ptr this_frame,
 169                               void **this_cache)
 170 {
 171   return UNWIND_OUTERMOST;
 172 }
 173
 174 /* Ask THIS_FRAME to unwind its register.  */
 175
 176 static struct value *
 177 bpf_frame_prev_register (frame_info_ptr this_frame,
 178                          void **this_prologue_cache, int regnum)
 179 {
 180   return frame_unwind_got_register (this_frame, regnum, regnum);
 181 }
 182
 183 /* Frame unwinder machinery for BPF.  */
 184
 185 static const struct frame_unwind bpf_frame_unwind =
 186 {
 187   "bpf prologue",
 188   NORMAL_FRAME,
 189   bpf_frame_unwind_stop_reason,
 190   bpf_frame_this_id,
 191   bpf_frame_prev_register,
 192   NULL,
 193   default_frame_sniffer
 194 };
 195
 196 \f
 197 /* Breakpoints.  */
 198
 199 /* Enum describing the different kinds of breakpoints.  We currently
 200    just support one, implemented by the brkpt xbpf instruction.   */
 201
 202 enum bpf_breakpoint_kinds
 203 {
 204   BPF_BP_KIND_BRKPT = 0,
 205 };
 206
 207 /* Implement the breakpoint_kind_from_pc gdbarch method.  */
 208
 209 static int
 210 bpf_breakpoint_kind_from_pc (struct gdbarch *gdbarch, CORE_ADDR *start_pc)
 211 {
 212   /* We support just one kind of breakpoint.  */
 213   return BPF_BP_KIND_BRKPT;
 214 }
 215
 216 /* Implement the sw_breakpoint_from_kind gdbarch method.  */
 217
 218 static const gdb_byte *
 219 bpf_sw_breakpoint_from_kind (struct gdbarch *gdbarch, int kind, int *size)
 220 {
 221   static unsigned char brkpt_insn[]
 222     = {0x8c, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
 223
 224   switch (kind)
 225     {
 226     case BPF_BP_KIND_BRKPT:
 227       *size = 8;
 228       return brkpt_insn;
 229     default:
 230       gdb_assert_not_reached ("unexpected BPF breakpoint kind");
 231     }
 232 }
 233
 234 \f
 235 /* Assuming THIS_FRAME is a dummy frame, return its frame ID.  */
 236
 237 static struct frame_id
 238 bpf_dummy_id (struct gdbarch *gdbarch, frame_info_ptr this_frame)
 239 {
 240   CORE_ADDR sp = get_frame_register_unsigned (this_frame,
 241                                               gdbarch_sp_regnum (gdbarch));
 242   return frame_id_build (sp, get_frame_pc (this_frame));
 243 }
 244
 245 /* Implement the push dummy call gdbarch callback.  */
 246
 247 static CORE_ADDR
 248 bpf_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
 249                      struct regcache *regcache, CORE_ADDR bp_addr,
 250                      int nargs, struct value **args, CORE_ADDR sp,
 251                      function_call_return_method return_method,
 252                      CORE_ADDR struct_addr)
 253 {
 254   gdb_printf (gdb_stdlog, "Pushing dummy call: sp=%s\n",
 255               paddress (gdbarch, sp));
 256   /* XXX writeme  */
 257   return sp;
 258 }
 259
 260 /* Extract a function return value of TYPE from REGCACHE,
 261    and copy it into VALBUF.  */
 262
 263 static void
 264 bpf_extract_return_value (struct type *type, struct regcache *regcache,
 265                           gdb_byte *valbuf)
 266 {
 267   int len = type->length ();
 268   gdb_byte vbuf[8];
 269
 270   gdb_assert (len <= 8);
 271   regcache->cooked_read (BPF_R0_REGNUM, vbuf);
 272   memcpy (valbuf, vbuf + 8 - len, len);
 273 }
 274
 275 /* Store the function return value of type TYPE from VALBUF into REGNAME.  */
 276
 277 static void
 278 bpf_store_return_value (struct type *type, struct regcache *regcache,
 279                         const gdb_byte *valbuf)
 280 {
 281   int len = type->length ();
 282   gdb_byte vbuf[8];
 283
 284   gdb_assert (len <= 8);
 285   memset (vbuf, 0, sizeof (vbuf));
 286   memcpy (vbuf + 8 - len, valbuf, len);
 287   regcache->cooked_write (BPF_R0_REGNUM, vbuf);
 288 }
 289
 290 /* Handle function's return value.  */
 291
 292 static enum return_value_convention
 293 bpf_return_value (struct gdbarch *gdbarch, struct value *function,
 294                   struct type *type, struct regcache *regcache,
 295                   gdb_byte *readbuf, const gdb_byte *writebuf)
 296 {
 297   int len = type->length ();
 298
 299   if (len > 8)
 300     return RETURN_VALUE_STRUCT_CONVENTION;
 301
 302   if (readbuf != NULL)
 303     bpf_extract_return_value (type, regcache, readbuf);
 304   if (writebuf != NULL)
 305     bpf_store_return_value (type, regcache, writebuf);
 306
 307   return RETURN_VALUE_REGISTER_CONVENTION;
 308 }
 309
 310 \f
 311 /* Initialize the current architecture based on INFO.  If possible, re-use an
 312    architecture from ARCHES, which is a list of architectures already created
 313    during this debugging session.  */
 314
 315 static struct gdbarch *
 316 bpf_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
 317 {
 318   /* If there is already a candidate, use it.  */
 319   arches = gdbarch_list_lookup_by_info (arches, &info);
 320   if (arches != NULL)
 321     return arches->gdbarch;
 322
 323   /* Allocate space for the new architecture.  */
 324   gdbarch *gdbarch
 325     = gdbarch_alloc (&info, gdbarch_tdep_up (new bpf_gdbarch_tdep));
 326
 327   /* Information about registers, etc.  */
 328   set_gdbarch_num_regs (gdbarch, BPF_NUM_REGS);
 329   set_gdbarch_register_name (gdbarch, bpf_register_name);
 330   set_gdbarch_register_type (gdbarch, bpf_register_type);
 331
 332   /* Register numbers of various important registers.  */
 333   set_gdbarch_sp_regnum (gdbarch, BPF_R10_REGNUM);
 334   set_gdbarch_pc_regnum (gdbarch, BPF_PC_REGNUM);
 335
 336   /* Map DWARF2 registers to GDB registers.  */
 337   set_gdbarch_dwarf2_reg_to_regnum (gdbarch, bpf_dwarf2_reg_to_regnum);
 338
 339   /* Call dummy code.  */
 340   set_gdbarch_call_dummy_location (gdbarch, ON_STACK);
 341   set_gdbarch_dummy_id (gdbarch, bpf_dummy_id);
 342   set_gdbarch_push_dummy_call (gdbarch, bpf_push_dummy_call);
 343
 344   /* Returning results.  */
 345   set_gdbarch_return_value (gdbarch, bpf_return_value);
 346
 347   /* Advance PC across function entry code.  */
 348   set_gdbarch_skip_prologue (gdbarch, bpf_skip_prologue);
 349
 350   /* Stack grows downward.  */
 351   set_gdbarch_inner_than (gdbarch, core_addr_lessthan);
 352
 353   /* Breakpoint manipulation.  */
 354   set_gdbarch_breakpoint_kind_from_pc (gdbarch, bpf_breakpoint_kind_from_pc);
 355   set_gdbarch_sw_breakpoint_from_kind (gdbarch, bpf_sw_breakpoint_from_kind);
 356
 357   /* Frame handling.  */
 358   set_gdbarch_frame_args_skip (gdbarch, 8);
 359
 360   /* Disassembly.  */
 361   set_gdbarch_print_insn (gdbarch, bpf_gdb_print_insn);
 362
 363   /* Hook in ABI-specific overrides, if they have been registered.  */
 364   gdbarch_init_osabi (info, gdbarch);
 365
 366   /* Install unwinders.  */
 367   frame_unwind_append_unwinder (gdbarch, &bpf_frame_unwind);
 368
 369   return gdbarch;
 370 }
 371
 372 void _initialize_bpf_tdep ();
 373 void
 374 _initialize_bpf_tdep ()
 375 {
 376   gdbarch_register (bfd_arch_bpf, bpf_gdbarch_init);
 377
 378   /* Add commands 'set/show debug bpf'.  */
 379   add_setshow_zuinteger_cmd ("bpf", class_maintenance,
 380                              &bpf_debug_flag,
 381                              _("Set BPF debugging."),
 382                              _("Show BPF debugging."),
 383                              _("Enables BPF specific debugging output."),
 384                              NULL,
 385                              &show_bpf_debug,
 386                              &setdebuglist, &showdebuglist);
 387 }