gas/config/tc-bpf.c

   1 /* tc-bpf.c -- Assembler for the Linux eBPF.
   2    Copyright (C) 2019-2020 Free Software Foundation, Inc.
   3    Contributed by Oracle, Inc.
   4
   5    This file is part of GAS, the GNU Assembler.
   6
   7    GAS 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, or (at your option)
  10    any later version.
  11
  12    GAS 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 GAS; see the file COPYING.  If not, write to
  19    the Free Software Foundation, 51 Franklin Street - Fifth Floor,
  20    Boston, MA 02110-1301, USA.  */
  21
  22 #include "as.h"
  23 #include "subsegs.h"
  24 #include "symcat.h"
  25 #include "opcodes/bpf-desc.h"
  26 #include "opcodes/bpf-opc.h"
  27 #include "cgen.h"
  28 #include "elf/common.h"
  29 #include "elf/bpf.h"
  30 #include "dwarf2dbg.h"
  31
  32 const char comment_chars[]        = ";";
  33 const char line_comment_chars[] = "#";
  34 const char line_separator_chars[] = "`";
  35 const char EXP_CHARS[]            = "eE";
  36 const char FLT_CHARS[]            = "fFdD";
  37
  38 /* Like s_lcomm_internal in gas/read.c but the alignment string
  39    is allowed to be optional.  */
  40
  41 static symbolS *
  42 pe_lcomm_internal (int needs_align, symbolS *symbolP, addressT size)
  43 {
  44   addressT align = 0;
  45
  46   SKIP_WHITESPACE ();
  47
  48   if (needs_align
  49       && *input_line_pointer == ',')
  50     {
  51       align = parse_align (needs_align - 1);
  52
  53       if (align == (addressT) -1)
  54         return NULL;
  55     }
  56   else
  57     {
  58       if (size >= 8)
  59         align = 3;
  60       else if (size >= 4)
  61         align = 2;
  62       else if (size >= 2)
  63         align = 1;
  64       else
  65         align = 0;
  66     }
  67
  68   bss_alloc (symbolP, size, align);
  69   return symbolP;
  70 }
  71
  72 static void
  73 pe_lcomm (int needs_align)
  74 {
  75   s_comm_internal (needs_align * 2, pe_lcomm_internal);
  76 }
  77
  78 /* The target specific pseudo-ops which we support.  */
  79 const pseudo_typeS md_pseudo_table[] =
  80 {
  81     { "half",      cons,              2 },
  82     { "word",      cons,              4 },
  83     { "dword",     cons,              8 },
  84     { "lcomm",     pe_lcomm,          1 },
  85     { NULL,        NULL,              0 }
  86 };
  87
  88 \f
  89
  90 /* ISA handling.  */
  91 static CGEN_BITSET *bpf_isa;
  92
  93 \f
  94
  95 /* Command-line options processing.  */
  96
  97 enum options
  98 {
  99   OPTION_LITTLE_ENDIAN = OPTION_MD_BASE,
 100   OPTION_BIG_ENDIAN
 101 };
 102
 103 struct option md_longopts[] =
 104 {
 105   { "EL", no_argument, NULL, OPTION_LITTLE_ENDIAN },
 106   { "EB", no_argument, NULL, OPTION_BIG_ENDIAN },
 107   { NULL,          no_argument, NULL, 0 },
 108 };
 109
 110 size_t md_longopts_size = sizeof (md_longopts);
 111
 112 const char * md_shortopts = "";
 113
 114 extern int target_big_endian;
 115
 116 /* Whether target_big_endian has been set while parsing command-line
 117    arguments.  */
 118 static int set_target_endian = 0;
 119
 120 int
 121 md_parse_option (int c, const char * arg ATTRIBUTE_UNUSED)
 122 {
 123   switch (c)
 124     {
 125     case OPTION_BIG_ENDIAN:
 126       set_target_endian = 1;
 127       target_big_endian = 1;
 128       break;
 129     case OPTION_LITTLE_ENDIAN:
 130       set_target_endian = 1;
 131       target_big_endian = 0;
 132       break;
 133     default:
 134       return 0;
 135     }
 136
 137   return 1;
 138 }
 139
 140 void
 141 md_show_usage (FILE * stream)
 142 {
 143   fprintf (stream, _("\nBPF options:\n"));
 144   fprintf (stream, _("\
 145   --EL                  generate code for a little endian machine\n\
 146   --EB                  generate code for a big endian machine\n"));
 147 }
 148
 149 \f
 150 void
 151 md_begin (void)
 152 {
 153   /* Initialize the `cgen' interface.  */
 154
 155   /* If not specified in the command line, use the host
 156      endianness.  */
 157   if (!set_target_endian)
 158     {
 159 #ifdef WORDS_BIGENDIAN
 160       target_big_endian = 1;
 161 #else
 162       target_big_endian = 0;
 163 #endif
 164     }
 165
 166   /* Set the ISA, which depends on the target endianness. */
 167   bpf_isa = cgen_bitset_create (ISA_MAX);
 168   if (target_big_endian)
 169     cgen_bitset_set (bpf_isa, ISA_EBPFBE);
 170   else
 171     cgen_bitset_set (bpf_isa, ISA_EBPFLE);
 172
 173   /* Set the machine number and endian.  */
 174   gas_cgen_cpu_desc = bpf_cgen_cpu_open (CGEN_CPU_OPEN_ENDIAN,
 175                                          target_big_endian ?
 176                                          CGEN_ENDIAN_BIG : CGEN_ENDIAN_LITTLE,
 177                                          CGEN_CPU_OPEN_INSN_ENDIAN,
 178                                          CGEN_ENDIAN_LITTLE,
 179                                          CGEN_CPU_OPEN_ISAS,
 180                                          bpf_isa,
 181                                          CGEN_CPU_OPEN_END);
 182   bpf_cgen_init_asm (gas_cgen_cpu_desc);
 183
 184   /* This is a callback from cgen to gas to parse operands.  */
 185   cgen_set_parse_operand_fn (gas_cgen_cpu_desc, gas_cgen_parse_operand);
 186
 187   /* Set the machine type. */
 188   bfd_default_set_arch_mach (stdoutput, bfd_arch_bpf, bfd_mach_bpf);
 189 }
 190
 191 valueT
 192 md_section_align (segT segment, valueT size)
 193 {
 194   int align = bfd_section_alignment (segment);
 195
 196   return ((size + (1 << align) - 1) & -(1 << align));
 197 }
 198
 199 \f
 200 /* Functions concerning relocs.  */
 201
 202 /* The location from which a PC relative jump should be calculated,
 203    given a PC relative reloc.  */
 204
 205 long
 206 md_pcrel_from_section (fixS *fixP, segT sec)
 207 {
 208   if (fixP->fx_addsy != (symbolS *) NULL
 209       && (! S_IS_DEFINED (fixP->fx_addsy)
 210           || (S_GET_SEGMENT (fixP->fx_addsy) != sec)
 211           || S_IS_EXTERNAL (fixP->fx_addsy)
 212           || S_IS_WEAK (fixP->fx_addsy)))
 213     {
 214         /* The symbol is undefined (or is defined but not in this section).
 215          Let the linker figure it out.  */
 216       return 0;
 217     }
 218
 219   return fixP->fx_where + fixP->fx_frag->fr_address;
 220 }
 221
 222 /* Write a value out to the object file, using the appropriate endianness.  */
 223
 224 void
 225 md_number_to_chars (char * buf, valueT val, int n)
 226 {
 227   if (target_big_endian)
 228     number_to_chars_bigendian (buf, val, n);
 229   else
 230     number_to_chars_littleendian (buf, val, n);
 231 }
 232
 233 arelent *
 234 tc_gen_reloc (asection *sec, fixS *fix)
 235 {
 236   return gas_cgen_tc_gen_reloc (sec, fix);
 237 }
 238
 239 /* Return the bfd reloc type for OPERAND of INSN at fixup FIXP.  This
 240    is called when the operand is an expression that couldn't be fully
 241    resolved.  Returns BFD_RELOC_NONE if no reloc type can be found.
 242    *FIXP may be modified if desired.  */
 243
 244 bfd_reloc_code_real_type
 245 md_cgen_lookup_reloc (const CGEN_INSN *insn ATTRIBUTE_UNUSED,
 246                       const CGEN_OPERAND *operand,
 247                       fixS *fixP)
 248 {
 249   switch (operand->type)
 250     {
 251     case BPF_OPERAND_OFFSET16:
 252       return BFD_RELOC_BPF_16;
 253     case BPF_OPERAND_IMM32:
 254       return BFD_RELOC_BPF_32;
 255     case BPF_OPERAND_IMM64:
 256       return BFD_RELOC_BPF_64;
 257     case BPF_OPERAND_DISP16:
 258       fixP->fx_pcrel = 1;
 259       return BFD_RELOC_BPF_DISP16;
 260     case BPF_OPERAND_DISP32:
 261       fixP->fx_pcrel = 1;
 262       return BFD_RELOC_BPF_DISP32;
 263     default:
 264       break;
 265     }
 266   return BFD_RELOC_NONE;
 267 }
 268 \f
 269 /* *FRAGP has been relaxed to its final size, and now needs to have
 270    the bytes inside it modified to conform to the new size.
 271
 272    Called after relaxation is finished.
 273    fragP->fr_type == rs_machine_dependent.
 274    fragP->fr_subtype is the subtype of what the address relaxed to.  */
 275
 276 void
 277 md_convert_frag (bfd *abfd ATTRIBUTE_UNUSED,
 278                  segT sec ATTRIBUTE_UNUSED,
 279                  fragS *fragP ATTRIBUTE_UNUSED)
 280 {
 281   as_fatal (_("convert_frag called"));
 282 }
 283
 284 int
 285 md_estimate_size_before_relax (fragS *fragP ATTRIBUTE_UNUSED,
 286                                segT segment ATTRIBUTE_UNUSED)
 287 {
 288   as_fatal (_("estimate_size_before_relax called"));
 289   return 0;
 290 }
 291
 292 \f
 293 void
 294 md_apply_fix (fixS *fixP, valueT *valP, segT seg)
 295 {
 296   /* Some fixups for instructions require special attention.  This is
 297      handled in the code block below.  */
 298   if ((int) fixP->fx_r_type >= (int) BFD_RELOC_UNUSED)
 299     {
 300       int opindex = (int) fixP->fx_r_type - (int) BFD_RELOC_UNUSED;
 301       const CGEN_OPERAND *operand = cgen_operand_lookup_by_num (gas_cgen_cpu_desc,
 302                                                                 opindex);
 303       char *where;
 304
 305       switch (operand->type)
 306         {
 307         case BPF_OPERAND_DISP32:
 308           /* eBPF supports two kind of CALL instructions: the so
 309              called pseudo calls ("bpf to bpf") and external calls
 310              ("bpf to kernel").
 311
 312              Both kind of calls use the same instruction (CALL).
 313              However, external calls are constructed by passing a
 314              constant argument to the instruction, whereas pseudo
 315              calls result from expressions involving symbols.  In
 316              practice, instructions requiring a fixup are interpreted
 317              as pseudo-calls.  If we are executing this code, this is
 318              a pseudo call.
 319
 320              The kernel expects for pseudo-calls to be annotated by
 321              having BPF_PSEUDO_CALL in the SRC field of the
 322              instruction.  But beware the infamous nibble-swapping of
 323              eBPF and take endianness into account here.
 324
 325              Note that the CALL instruction has only one operand, so
 326              this code is executed only once per instruction.  */
 327           where = fixP->fx_frag->fr_literal + fixP->fx_where;
 328           where[1] = target_big_endian ? 0x01 : 0x10;
 329           /* Fallthrough.  */
 330         case BPF_OPERAND_DISP16:
 331           /* The PC-relative displacement fields in jump instructions
 332              shouldn't be in bytes.  Instead, they hold the number of
 333              64-bit words to the target, _minus one_.  */
 334           *valP = (((long) (*valP)) - 8) / 8;
 335           break;
 336         default:
 337           break;
 338         }
 339     }
 340
 341   /* And now invoke CGEN's handler, which will eventually install
 342      *valP into the corresponding operand.  */
 343   gas_cgen_md_apply_fix (fixP, valP, seg);
 344 }
 345
 346 void
 347 md_assemble (char *str)
 348 {
 349   const CGEN_INSN *insn;
 350   char *errmsg;
 351   CGEN_FIELDS fields;
 352
 353 #if CGEN_INT_INSN_P
 354   CGEN_INSN_INT buffer[CGEN_MAX_INSN_SIZE / sizeof (CGEN_INT_INSN_P)];
 355 #else
 356   unsigned char buffer[CGEN_MAX_INSN_SIZE];
 357 #endif
 358
 359   gas_cgen_init_parse ();
 360   insn = bpf_cgen_assemble_insn (gas_cgen_cpu_desc, str, &fields,
 361                                   buffer, &errmsg);
 362
 363   if (insn == NULL)
 364     {
 365       as_bad ("%s", errmsg);
 366       return;
 367     }
 368
 369   gas_cgen_finish_insn (insn, buffer, CGEN_FIELDS_BITSIZE (&fields),
 370                         0, /* zero to ban relaxable insns.  */
 371                         NULL); /* NULL so results not returned here.  */
 372 }
 373
 374 void
 375 md_operand (expressionS *expressionP)
 376 {
 377   gas_cgen_md_operand (expressionP);
 378 }
 379
 380
 381 symbolS *
 382 md_undefined_symbol (char *name ATTRIBUTE_UNUSED)
 383 {
 384   return NULL;
 385 }
 386
 387 \f
 388 /* Turn a string in input_line_pointer into a floating point constant
 389    of type TYPE, and store the appropriate bytes in *LITP.  The number
 390    of LITTLENUMS emitted is stored in *SIZEP.  An error message is
 391    returned, or NULL on OK.  */
 392
 393 const char *
 394 md_atof (int type, char *litP, int *sizeP)
 395 {
 396   return ieee_md_atof (type, litP, sizeP, FALSE);
 397 }