gdb/bpf-tdep.c

   1 /* Target-dependent code for BPF.
   2
   3    Copyright (C) 2020-2025 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-utils.h"
  21 #include "dis-asm.h"
  22 #include "frame.h"
  23 #include "frame-unwind.h"
  24 #include "trad-frame.h"
  25 #include "symtab.h"
  26 #include "value.h"
  27 #include "cli/cli-cmds.h"
  28 #include "breakpoint.h"
  29 #include "inferior.h"
  30 #include "regcache.h"
  31 #include "target.h"
  32 #include "dwarf2/frame.h"
  33 #include "osabi.h"
  34 #include "target-descriptions.h"
  35 #include "remote.h"
  36 #include "gdbarch.h"
  37
  38 \f
  39 /* eBPF registers.  */
  40
  41 enum bpf_regnum
  42 {
  43   BPF_R0_REGNUM,                /* return value */
  44   BPF_R1_REGNUM,
  45   BPF_R2_REGNUM,
  46   BPF_R3_REGNUM,
  47   BPF_R4_REGNUM,
  48   BPF_R5_REGNUM,
  49   BPF_R6_REGNUM,
  50   BPF_R7_REGNUM,
  51   BPF_R8_REGNUM,
  52   BPF_R9_REGNUM,
  53   BPF_R10_REGNUM,               /* sp */
  54   BPF_PC_REGNUM,
  55 };
  56
  57 #define BPF_NUM_REGS    (BPF_PC_REGNUM + 1)
  58
  59 /* Target-dependent structure in gdbarch.  */
  60 struct bpf_gdbarch_tdep : gdbarch_tdep_base
  61 {
  62 };
  63
  64 \f
  65 /* Internal debugging facilities.  */
  66
  67 /* When this is set to non-zero debugging information will be
  68    printed.  */
  69
  70 static unsigned int bpf_debug_flag = 0;
  71
  72 /* The show callback for 'show debug bpf'.  */
  73
  74 static void
  75 show_bpf_debug (struct ui_file *file, int from_tty,
  76                 struct cmd_list_element *c, const char *value)
  77 {
  78   gdb_printf (file, _("Debugging of BPF is %s.\n"), value);
  79 }
  80
  81 \f
  82 /* BPF registers.  */
  83
  84 static const char *bpf_register_names[] =
  85 {
  86   "r0",   "r1",  "r2",    "r3",   "r4",   "r5",   "r6",   "r7",
  87   "r8",   "r9",  "r10",   "pc"
  88 };
  89
  90 /* Return the name of register REGNUM.  */
  91
  92 static const char *
  93 bpf_register_name (struct gdbarch *gdbarch, int reg)
  94 {
  95   static_assert (ARRAY_SIZE (bpf_register_names) == BPF_NUM_REGS);
  96   return bpf_register_names[reg];
  97 }
  98
  99 /* Return the GDB type of register REGNUM.  */
 100
 101 static struct type *
 102 bpf_register_type (struct gdbarch *gdbarch, int reg)
 103 {
 104   if (reg == BPF_R10_REGNUM)
 105     return builtin_type (gdbarch)->builtin_data_ptr;
 106   else if (reg == BPF_PC_REGNUM)
 107     return builtin_type (gdbarch)->builtin_func_ptr;
 108   return builtin_type (gdbarch)->builtin_int64;
 109 }
 110
 111 /* Return the GDB register number corresponding to DWARF's REG.  */
 112
 113 static int
 114 bpf_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int reg)
 115 {
 116   if (reg >= 0 && reg < BPF_NUM_REGS)
 117     return reg;
 118   return -1;
 119 }
 120
 121 /* Implement the "print_insn" gdbarch method.  */
 122
 123 static int
 124 bpf_gdb_print_insn (bfd_vma memaddr, disassemble_info *info)
 125 {
 126   info->symbols = NULL;
 127   return default_print_insn (memaddr, info);
 128 }
 129
 130 \f
 131 /* Return PC of first real instruction of the function starting at
 132    START_PC.  */
 133
 134 static CORE_ADDR
 135 bpf_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR start_pc)
 136 {
 137   gdb_printf (gdb_stdlog,
 138               "Skipping prologue: start_pc=%s\n",
 139               paddress (gdbarch, start_pc));
 140   /* XXX: to be completed.  */
 141   return start_pc + 0;
 142 }
 143
 144 \f
 145 /* Frame unwinder.
 146
 147    XXX it is not clear how to unwind in eBPF, since the stack is not
 148    guaranteed to be contiguous, and therefore no relative stack
 149    addressing can be done in the callee in order to access the
 150    caller's stack frame.  To explore with xBPF, which will relax this
 151    restriction.  */
 152
 153 /* Given THIS_FRAME, return its ID.  */
 154
 155 static void
 156 bpf_frame_this_id (const frame_info_ptr &this_frame,
 157                    void **this_prologue_cache,
 158                    struct frame_id *this_id)
 159 {
 160   /* Note that THIS_ID defaults to the outermost frame if we don't set
 161      anything here.  See frame.c:compute_frame_id.  */
 162 }
 163
 164 /* Return the reason why we can't unwind past THIS_FRAME.  */
 165
 166 static enum unwind_stop_reason
 167 bpf_frame_unwind_stop_reason (const frame_info_ptr &this_frame,
 168                               void **this_cache)
 169 {
 170   return UNWIND_OUTERMOST;
 171 }
 172
 173 /* Ask THIS_FRAME to unwind its register.  */
 174
 175 static struct value *
 176 bpf_frame_prev_register (const frame_info_ptr &this_frame,
 177                          void **this_prologue_cache, int regnum)
 178 {
 179   return frame_unwind_got_register (this_frame, regnum, regnum);
 180 }
 181
 182 /* Frame unwinder machinery for BPF.  */
 183
 184 static const struct frame_unwind_legacy bpf_frame_unwind (
 185   "bpf prologue",
 186   NORMAL_FRAME,
 187   FRAME_UNWIND_ARCH,
 188   bpf_frame_unwind_stop_reason,
 189   bpf_frame_this_id,
 190   bpf_frame_prev_register,
 191   NULL,
 192   default_frame_sniffer
 193 );
 194
 195 \f
 196 /* Breakpoints.  */
 197
 198 /* Enum describing the different kinds of breakpoints.  We currently
 199    just support one, implemented by the brkpt xbpf instruction.   */
 200
 201 enum bpf_breakpoint_kinds
 202 {
 203   BPF_BP_KIND_BRKPT = 0,
 204 };
 205
 206 /* Implement the breakpoint_kind_from_pc gdbarch method.  */
 207
 208 static int
 209 bpf_breakpoint_kind_from_pc (struct gdbarch *gdbarch, CORE_ADDR *start_pc)
 210 {
 211   /* We support just one kind of breakpoint.  */
 212   return BPF_BP_KIND_BRKPT;
 213 }
 214
 215 /* Implement the sw_breakpoint_from_kind gdbarch method.  */
 216
 217 static const gdb_byte *
 218 bpf_sw_breakpoint_from_kind (struct gdbarch *gdbarch, int kind, int *size)
 219 {
 220   static unsigned char brkpt_insn[]
 221     = {0x8c, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
 222
 223   switch (kind)
 224     {
 225     case BPF_BP_KIND_BRKPT:
 226       *size = 8;
 227       return brkpt_insn;
 228     default:
 229       gdb_assert_not_reached ("unexpected BPF breakpoint kind");
 230     }
 231 }
 232
 233 \f
 234 /* Assuming THIS_FRAME is a dummy frame, return its frame ID.  */
 235
 236 static struct frame_id
 237 bpf_dummy_id (struct gdbarch *gdbarch, const frame_info_ptr &this_frame)
 238 {
 239   CORE_ADDR sp = get_frame_register_unsigned (this_frame,
 240                                               gdbarch_sp_regnum (gdbarch));
 241   return frame_id_build (sp, get_frame_pc (this_frame));
 242 }
 243
 244 /* Implement the push dummy call gdbarch callback.  */
 245
 246 static CORE_ADDR
 247 bpf_push_dummy_call (struct gdbarch *gdbarch, struct value *function,
 248                      struct regcache *regcache, CORE_ADDR bp_addr,
 249                      int nargs, struct value **args, CORE_ADDR sp,
 250                      function_call_return_method return_method,
 251                      CORE_ADDR struct_addr)
 252 {
 253   gdb_printf (gdb_stdlog, "Pushing dummy call: sp=%s\n",
 254               paddress (gdbarch, sp));
 255   /* XXX writeme  */
 256   return sp;
 257 }
 258
 259 /* Extract a function return value of TYPE from REGCACHE,
 260    and copy it into VALBUF.  */
 261
 262 static void
 263 bpf_extract_return_value (struct type *type, struct regcache *regcache,
 264                           gdb_byte *valbuf)
 265 {
 266   int len = type->length ();
 267   gdb_byte vbuf[8];
 268
 269   gdb_assert (len <= 8);
 270   regcache->cooked_read (BPF_R0_REGNUM, vbuf);
 271   memcpy (valbuf, vbuf + 8 - len, len);
 272 }
 273
 274 /* Store the function return value of type TYPE from VALBUF into REGNAME.  */
 275
 276 static void
 277 bpf_store_return_value (struct type *type, struct regcache *regcache,
 278                         const gdb_byte *valbuf)
 279 {
 280   int len = type->length ();
 281   gdb_byte vbuf[8];
 282
 283   gdb_assert (len <= 8);
 284   memset (vbuf, 0, sizeof (vbuf));
 285   memcpy (vbuf + 8 - len, valbuf, len);
 286   regcache->cooked_write (BPF_R0_REGNUM, vbuf);
 287 }
 288
 289 /* Handle function's return value.  */
 290
 291 static enum return_value_convention
 292 bpf_return_value (struct gdbarch *gdbarch, struct value *function,
 293                   struct type *type, struct regcache *regcache,
 294                   gdb_byte *readbuf, const gdb_byte *writebuf)
 295 {
 296   int len = type->length ();
 297
 298   if (len > 8)
 299     return RETURN_VALUE_STRUCT_CONVENTION;
 300
 301   if (readbuf != NULL)
 302     bpf_extract_return_value (type, regcache, readbuf);
 303   if (writebuf != NULL)
 304     bpf_store_return_value (type, regcache, writebuf);
 305
 306   return RETURN_VALUE_REGISTER_CONVENTION;
 307 }
 308
 309 \f
 310 /* Initialize the current architecture based on INFO.  If possible, reuse an
 311    architecture from ARCHES, which is a list of architectures already created
 312    during this debugging session.  */
 313
 314 static struct gdbarch *
 315 bpf_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
 316 {
 317   /* If there is already a candidate, use it.  */
 318   arches = gdbarch_list_lookup_by_info (arches, &info);
 319   if (arches != NULL)
 320     return arches->gdbarch;
 321
 322   /* Allocate space for the new architecture.  */
 323   gdbarch *gdbarch
 324     = gdbarch_alloc (&info, gdbarch_tdep_up (new bpf_gdbarch_tdep));
 325
 326   /* Information about registers, etc.  */
 327   set_gdbarch_num_regs (gdbarch, BPF_NUM_REGS);
 328   set_gdbarch_register_name (gdbarch, bpf_register_name);
 329   set_gdbarch_register_type (gdbarch, bpf_register_type);
 330
 331   /* Register numbers of various important registers.  */
 332   set_gdbarch_sp_regnum (gdbarch, BPF_R10_REGNUM);
 333   set_gdbarch_pc_regnum (gdbarch, BPF_PC_REGNUM);
 334
 335   /* Map DWARF2 registers to GDB registers.  */
 336   set_gdbarch_dwarf2_reg_to_regnum (gdbarch, bpf_dwarf2_reg_to_regnum);
 337
 338   /* Call dummy code.  */
 339   set_gdbarch_call_dummy_location (gdbarch, ON_STACK);
 340   set_gdbarch_dummy_id (gdbarch, bpf_dummy_id);
 341   set_gdbarch_push_dummy_call (gdbarch, bpf_push_dummy_call);
 342
 343   /* Returning results.  */
 344   set_gdbarch_return_value (gdbarch, bpf_return_value);
 345
 346   /* Advance PC across function entry code.  */
 347   set_gdbarch_skip_prologue (gdbarch, bpf_skip_prologue);
 348
 349   /* Stack grows downward.  */
 350   set_gdbarch_inner_than (gdbarch, core_addr_lessthan);
 351
 352   /* Breakpoint manipulation.  */
 353   set_gdbarch_breakpoint_kind_from_pc (gdbarch, bpf_breakpoint_kind_from_pc);
 354   set_gdbarch_sw_breakpoint_from_kind (gdbarch, bpf_sw_breakpoint_from_kind);
 355
 356   /* Frame handling.  */
 357   set_gdbarch_frame_args_skip (gdbarch, 8);
 358
 359   /* Disassembly.  */
 360   set_gdbarch_print_insn (gdbarch, bpf_gdb_print_insn);
 361
 362   /* Hook in ABI-specific overrides, if they have been registered.  */
 363   gdbarch_init_osabi (info, gdbarch);
 364
 365   /* Install unwinders.  */
 366   frame_unwind_append_unwinder (gdbarch, &bpf_frame_unwind);
 367
 368   return gdbarch;
 369 }
 370
 371 INIT_GDB_FILE (bpf_tdep)
 372 {
 373   gdbarch_register (bfd_arch_bpf, bpf_gdbarch_init);
 374
 375   /* Add commands 'set/show debug bpf'.  */
 376   add_setshow_zuinteger_cmd ("bpf", class_maintenance,
 377                              &bpf_debug_flag,
 378                              _("Set BPF debugging."),
 379                              _("Show BPF debugging."),
 380                              _("Enables BPF specific debugging output."),
 381                              NULL,
 382                              &show_bpf_debug,
 383                              &setdebuglist, &showdebuglist);
 384 }