401 lines
11 KiB
C
401 lines
11 KiB
C
/* tc-bpf.c -- Assembler for the Linux eBPF.
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Copyright (C) 2019 Free Software Foundation, Inc.
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Contributed by Oracle, Inc.
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This file is part of GAS, the GNU Assembler.
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GAS is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3, or (at your option)
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any later version.
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GAS is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GAS; see the file COPYING. If not, write to
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the Free Software Foundation, 51 Franklin Street - Fifth Floor,
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Boston, MA 02110-1301, USA. */
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#include "as.h"
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#include "subsegs.h"
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#include "symcat.h"
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#include "opcodes/bpf-desc.h"
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#include "opcodes/bpf-opc.h"
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#include "cgen.h"
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#include "elf/common.h"
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#include "elf/bpf.h"
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#include "dwarf2dbg.h"
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const char comment_chars[] = ";";
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const char line_comment_chars[] = "#";
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const char line_separator_chars[] = "`";
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const char EXP_CHARS[] = "eE";
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const char FLT_CHARS[] = "fFdD";
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/* Like s_lcomm_internal in gas/read.c but the alignment string
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is allowed to be optional. */
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static symbolS *
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pe_lcomm_internal (int needs_align, symbolS *symbolP, addressT size)
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{
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addressT align = 0;
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SKIP_WHITESPACE ();
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if (needs_align
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&& *input_line_pointer == ',')
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{
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align = parse_align (needs_align - 1);
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if (align == (addressT) -1)
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return NULL;
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}
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else
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{
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if (size >= 8)
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align = 3;
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else if (size >= 4)
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align = 2;
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else if (size >= 2)
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align = 1;
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else
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align = 0;
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}
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bss_alloc (symbolP, size, align);
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return symbolP;
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}
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static void
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pe_lcomm (int needs_align)
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{
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s_comm_internal (needs_align * 2, pe_lcomm_internal);
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}
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/* The target specific pseudo-ops which we support. */
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const pseudo_typeS md_pseudo_table[] =
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{
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{ "half", cons, 2 },
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{ "word", cons, 4 },
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{ "dword", cons, 8 },
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{ "lcomm", pe_lcomm, 1 },
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{ NULL, NULL, 0 }
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};
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/* ISA handling. */
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static CGEN_BITSET *bpf_isa;
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/* Command-line options processing. */
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enum options
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{
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OPTION_LITTLE_ENDIAN = OPTION_MD_BASE,
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OPTION_BIG_ENDIAN
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};
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struct option md_longopts[] =
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{
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{ "EL", no_argument, NULL, OPTION_LITTLE_ENDIAN },
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{ "EB", no_argument, NULL, OPTION_BIG_ENDIAN },
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{ NULL, no_argument, NULL, 0 },
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};
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size_t md_longopts_size = sizeof (md_longopts);
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const char * md_shortopts = "";
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extern int target_big_endian;
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/* Whether target_big_endian has been set while parsing command-line
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arguments. */
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static int set_target_endian = 0;
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int
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md_parse_option (int c, const char * arg ATTRIBUTE_UNUSED)
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{
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switch (c)
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{
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case OPTION_BIG_ENDIAN:
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set_target_endian = 1;
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target_big_endian = 1;
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break;
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case OPTION_LITTLE_ENDIAN:
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set_target_endian = 1;
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target_big_endian = 0;
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break;
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default:
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return 0;
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}
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return 1;
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}
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void
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md_show_usage (FILE * stream)
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{
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fprintf (stream, _("\nBPF options:\n"));
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fprintf (stream, _("\
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--EL generate code for a little endian machine\n\
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--EB generate code for a big endian machine\n"));
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}
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void
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md_begin (void)
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{
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/* Initialize the `cgen' interface. */
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/* If not specified in the command line, use the host
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endianness. */
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if (!set_target_endian)
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{
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#ifdef WORDS_BIGENDIAN
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target_big_endian = 1;
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#else
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target_big_endian = 0;
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#endif
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}
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/* Set the ISA, which depends on the target endianness. */
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bpf_isa = cgen_bitset_create (ISA_MAX);
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if (target_big_endian)
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cgen_bitset_set (bpf_isa, ISA_EBPFBE);
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else
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cgen_bitset_set (bpf_isa, ISA_EBPFLE);
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/* Set the machine number and endian. */
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gas_cgen_cpu_desc = bpf_cgen_cpu_open (CGEN_CPU_OPEN_ENDIAN,
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target_big_endian ?
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CGEN_ENDIAN_BIG : CGEN_ENDIAN_LITTLE,
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CGEN_CPU_OPEN_ISAS,
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bpf_isa,
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CGEN_CPU_OPEN_END);
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bpf_cgen_init_asm (gas_cgen_cpu_desc);
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/* This is a callback from cgen to gas to parse operands. */
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cgen_set_parse_operand_fn (gas_cgen_cpu_desc, gas_cgen_parse_operand);
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/* Set the machine type. */
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bfd_default_set_arch_mach (stdoutput, bfd_arch_bpf, bfd_mach_bpf);
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}
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valueT
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md_section_align (segT segment, valueT size)
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{
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int align = bfd_get_section_alignment (stdoutput, segment);
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return ((size + (1 << align) - 1) & -(1 << align));
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}
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/* Functions concerning relocs. */
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/* The location from which a PC relative jump should be calculated,
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given a PC relative reloc. */
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long
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md_pcrel_from_section (fixS *fixP, segT sec)
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{
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if (fixP->fx_addsy != (symbolS *) NULL
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&& (! S_IS_DEFINED (fixP->fx_addsy)
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|| (S_GET_SEGMENT (fixP->fx_addsy) != sec)
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|| S_IS_EXTERNAL (fixP->fx_addsy)
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|| S_IS_WEAK (fixP->fx_addsy)))
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{
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/* The symbol is undefined (or is defined but not in this section).
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Let the linker figure it out. */
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return 0;
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}
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return fixP->fx_where + fixP->fx_frag->fr_address;
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}
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/* Write a value out to the object file, using the appropriate endianness. */
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void
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md_number_to_chars (char * buf, valueT val, int n)
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{
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if (target_big_endian)
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number_to_chars_bigendian (buf, val, n);
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else
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number_to_chars_littleendian (buf, val, n);
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}
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arelent *
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tc_gen_reloc (asection *sec, fixS *fix)
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{
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return gas_cgen_tc_gen_reloc (sec, fix);
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}
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/* Return the bfd reloc type for OPERAND of INSN at fixup FIXP. This
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is called when the operand is an expression that couldn't be fully
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resolved. Returns BFD_RELOC_NONE if no reloc type can be found.
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*FIXP may be modified if desired. */
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bfd_reloc_code_real_type
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md_cgen_lookup_reloc (const CGEN_INSN *insn ATTRIBUTE_UNUSED,
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const CGEN_OPERAND *operand,
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fixS *fixP)
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{
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switch (operand->type)
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{
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case BPF_OPERAND_OFFSET16:
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return BFD_RELOC_BPF_16;
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case BPF_OPERAND_IMM32:
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return BFD_RELOC_BPF_32;
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case BPF_OPERAND_IMM64:
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return BFD_RELOC_BPF_64;
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case BPF_OPERAND_DISP16:
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fixP->fx_pcrel = 1;
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return BFD_RELOC_BPF_DISP16;
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case BPF_OPERAND_DISP32:
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fixP->fx_pcrel = 1;
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return BFD_RELOC_BPF_DISP32;
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default:
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break;
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}
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return BFD_RELOC_NONE;
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}
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/* *FRAGP has been relaxed to its final size, and now needs to have
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the bytes inside it modified to conform to the new size.
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Called after relaxation is finished.
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fragP->fr_type == rs_machine_dependent.
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fragP->fr_subtype is the subtype of what the address relaxed to. */
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void
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md_convert_frag (bfd *abfd ATTRIBUTE_UNUSED,
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segT sec ATTRIBUTE_UNUSED,
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fragS *fragP ATTRIBUTE_UNUSED)
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{
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as_fatal (_("convert_frag called"));
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}
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int
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md_estimate_size_before_relax (fragS *fragP ATTRIBUTE_UNUSED,
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segT segment ATTRIBUTE_UNUSED)
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{
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as_fatal (_("estimate_size_before_relax called"));
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return 0;
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}
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void
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md_apply_fix (fixS *fixP, valueT *valP, segT seg)
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{
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/* Some fixups for instructions require special attention. This is
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handled in the code block below. */
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if ((int) fixP->fx_r_type >= (int) BFD_RELOC_UNUSED)
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{
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int opindex = (int) fixP->fx_r_type - (int) BFD_RELOC_UNUSED;
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const CGEN_OPERAND *operand = cgen_operand_lookup_by_num (gas_cgen_cpu_desc,
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opindex);
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char *where;
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switch (operand->type)
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{
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case BPF_OPERAND_DISP32:
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/* eBPF supports two kind of CALL instructions: the so
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called pseudo calls ("bpf to bpf") and external calls
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("bpf to kernel").
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Both kind of calls use the same instruction (CALL).
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However, external calls are constructed by passing a
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constant argument to the instruction, whereas pseudo
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calls result from expressions involving symbols. In
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practice, instructions requiring a fixup are interpreted
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as pseudo-calls. If we are executing this code, this is
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a pseudo call.
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The kernel expects for pseudo-calls to be annotated by
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having BPF_PSEUDO_CALL in the SRC field of the
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instruction. But beware the infamous nibble-swapping of
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eBPF and take endianness into account here.
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Note that the CALL instruction has only one operand, so
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this code is executed only once per instruction. */
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where = fixP->fx_frag->fr_literal + fixP->fx_where;
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cgen_put_insn_value (gas_cgen_cpu_desc, (unsigned char *) where + 1, 8,
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target_big_endian ? 0x01 : 0x10);
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/* Fallthrough. */
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case BPF_OPERAND_DISP16:
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/* The PC-relative displacement fields in jump instructions
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shouldn't be in bytes. Instead, they hold the number of
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64-bit words to the target, _minus one_. */
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*valP = (((long) (*valP)) - 8) / 8;
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break;
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default:
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break;
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}
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}
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/* And now invoke CGEN's handler, which will eventually install
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*valP into the corresponding operand. */
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gas_cgen_md_apply_fix (fixP, valP, seg);
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}
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void
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md_assemble (char *str)
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{
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const CGEN_INSN *insn;
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char *errmsg;
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CGEN_FIELDS fields;
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#if CGEN_INT_INSN_P
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CGEN_INSN_INT buffer[CGEN_MAX_INSN_SIZE / sizeof (CGEN_INT_INSN_P)];
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#else
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unsigned char buffer[CGEN_MAX_INSN_SIZE];
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memset (buffer, 0, CGEN_MAX_INSN_SIZE); /* XXX to remove when CGEN
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is fixed to handle
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opcodes-in-words
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properly. */
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#endif
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gas_cgen_init_parse ();
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insn = bpf_cgen_assemble_insn (gas_cgen_cpu_desc, str, &fields,
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buffer, &errmsg);
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if (insn == NULL)
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{
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as_bad ("%s", errmsg);
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return;
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}
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gas_cgen_finish_insn (insn, buffer, CGEN_FIELDS_BITSIZE (&fields),
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0, /* zero to ban relaxable insns. */
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NULL); /* NULL so results not returned here. */
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}
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void
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md_operand (expressionS *expressionP)
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{
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gas_cgen_md_operand (expressionP);
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}
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symbolS *
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md_undefined_symbol (char *name ATTRIBUTE_UNUSED)
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{
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return NULL;
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}
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/* Turn a string in input_line_pointer into a floating point constant
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of type TYPE, and store the appropriate bytes in *LITP. The number
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of LITTLENUMS emitted is stored in *SIZEP. An error message is
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returned, or NULL on OK. */
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const char *
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md_atof (int type, char *litP, int *sizeP)
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{
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return ieee_md_atof (type, litP, sizeP, FALSE);
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}
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