Add support for ARM ELF Mapping symbols
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Nick Clifton
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@ -1,3 +1,17 @@
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2003-11-13 Nick Clifton <nickc@redhat.com>
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* tc-arm.c (mapping_state): New function. Emit a mapping
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symbol if necessary.
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(arm_elf_change_section): New function. Intercept section
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changes and generate mapping symbols.
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(s_bss): Likewise.
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(s_arm_elf_cons): Likewise.
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(opcode_select): Choose the correct mapping state.
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(md_assemble): Likewise.
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* tc-arm.h (md_elf_section_change_hook): Define.
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* doc/c-arm.texi (ARM Mapping Symbols): New node.
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* NEWS: Mention new feature.
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2003-11-12 Daniel Jacobowitz <drow@mvista.com>
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* Makefile.am (install, install-info, RECURSIVE_TARGETS): Define.
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@ -2646,6 +2646,178 @@ validate_offset_imm (val, hwse)
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return val;
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}
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#ifdef OBJ_ELF
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enum mstate
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{
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MAP_DATA,
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MAP_ARM,
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MAP_THUMB
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};
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/* This code is to handle mapping symbols as defined in the ARM ELF spec.
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(This text is taken from version B-02 of the spec):
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4.4.7 Mapping and tagging symbols
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A section of an ARM ELF file can contain a mixture of ARM code,
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Thumb code, and data. There are inline transitions between code
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and data at literal pool boundaries. There can also be inline
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transitions between ARM code and Thumb code, for example in
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ARM-Thumb inter-working veneers. Linkers, machine-level
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debuggers, profiling tools, and disassembly tools need to map
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images accurately. For example, setting an ARM breakpoint on a
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Thumb location, or in a literal pool, can crash the program
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being debugged, ruining the debugging session.
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ARM ELF entities are mapped (see section 4.4.7.1 below) and
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tagged (see section 4.4.7.2 below) using local symbols (with
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binding STB_LOCAL). To assist consumers, mapping and tagging
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symbols should be collated first in the symbol table, before
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other symbols with binding STB_LOCAL.
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To allow properly collated mapping and tagging symbols to be
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skipped by consumers that have no interest in them, the first
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such symbol should have the name $m and its st_value field equal
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to the total number of mapping and tagging symbols (including
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the $m) in the symbol table.
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4.4.7.1 Mapping symbols
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$a Labels the first byte of a sequence of ARM instructions.
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Its type is STT_FUNC.
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$d Labels the first byte of a sequence of data items.
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Its type is STT_OBJECT.
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$t Labels the first byte of a sequence of Thumb instructions.
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Its type is STT_FUNC.
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This list of mapping symbols may be extended in the future.
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Section-relative mapping symbols
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Mapping symbols defined in a section define a sequence of
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half-open address intervals that cover the address range of the
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section. Each interval starts at the address defined by a
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mapping symbol, and continues up to, but not including, the
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address defined by the next (in address order) mapping symbol or
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the end of the section. A corollary is that there must be a
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mapping symbol defined at the beginning of each section.
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Consumers can ignore the size of a section-relative mapping
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symbol. Producers can set it to 0.
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Absolute mapping symbols
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Because of the need to crystallize a Thumb address with the
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Thumb-bit set, absolute symbol of type STT_FUNC (symbols of type
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STT_FUNC defined in section SHN_ABS) need to be mapped with $a
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or $t.
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The extent of a mapping symbol defined in SHN_ABS is [st_value,
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st_value + st_size), or [st_value, st_value + 1) if st_size = 0,
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where [x, y) denotes the half-open address range from x,
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inclusive, to y, exclusive.
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In the absence of a mapping symbol, a consumer can interpret a
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function symbol with an odd value as the Thumb code address
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obtained by clearing the least significant bit of the
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value. This interpretation is deprecated, and it may not work in
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the future.
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Note - the Tagging symbols ($b, $f, $p $m) have been dropped from
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the EABI (which is still under development), so they are not
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implemented here. */
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static void
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mapping_state (enum mstate state)
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{
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static enum mstate mapstate = MAP_DATA;
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symbolS * symbolP;
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const char * symname;
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int type;
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if (mapstate == state)
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/* The mapping symbol has already been emitted.
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There is nothing else to do. */
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return;
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mapstate = state;
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switch (state)
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{
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case MAP_DATA:
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symname = "$d";
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type = BSF_OBJECT;
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break;
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case MAP_ARM:
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symname = "$a";
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type = BSF_FUNCTION;
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break;
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case MAP_THUMB:
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symname = "$t";
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type = BSF_FUNCTION;
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break;
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default:
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abort ();
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}
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symbolP = symbol_new (symname, now_seg, (valueT) frag_now_fix (), frag_now);
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symbol_table_insert (symbolP);
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symbol_get_bfdsym (symbolP)->flags |= type | BSF_LOCAL;
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switch (state)
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{
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case MAP_ARM:
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THUMB_SET_FUNC (symbolP, 0);
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ARM_SET_THUMB (symbolP, 0);
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ARM_SET_INTERWORK (symbolP, support_interwork);
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break;
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case MAP_THUMB:
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THUMB_SET_FUNC (symbolP, 1);
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ARM_SET_THUMB (symbolP, 1);
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ARM_SET_INTERWORK (symbolP, support_interwork);
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break;
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case MAP_DATA:
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default:
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return;
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}
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}
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/* When we change sections we need to issue a new mapping symbol. */
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static void
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arm_elf_change_section (void)
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{
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flagword flags;
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if (!SEG_NORMAL (now_seg))
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return;
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flags = bfd_get_section_flags (stdoutput, now_seg);
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/* We can ignore sections that only contain debug info. */
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if ((flags & SEC_ALLOC) == 0)
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return;
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if (flags & SEC_CODE)
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{
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if (thumb_mode)
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mapping_state (MAP_THUMB);
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else
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mapping_state (MAP_ARM);
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}
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else
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/* This section does not contain code. Therefore it must contain data. */
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mapping_state (MAP_DATA);
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}
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#else
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#define mapping_state(a)
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#endif /* OBJ_ELF */
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static void
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s_req (a)
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int a ATTRIBUTE_UNUSED;
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@ -2732,6 +2904,7 @@ s_bss (ignore)
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marking in_bss, then looking at s_skip for clues. */
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subseg_set (bss_section, 0);
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demand_empty_rest_of_line ();
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mapping_state (MAP_DATA);
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}
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static void
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@ -2970,6 +3143,7 @@ opcode_select (width)
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coming from ARM mode, which is word-aligned. */
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record_alignment (now_seg, 1);
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}
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mapping_state (MAP_THUMB);
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break;
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case 32:
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@ -2985,6 +3159,7 @@ opcode_select (width)
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record_alignment (now_seg, 1);
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}
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mapping_state (MAP_ARM);
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break;
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default:
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@ -11681,6 +11856,7 @@ md_assemble (str)
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return;
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}
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mapping_state (MAP_THUMB);
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inst.instruction = opcode->value;
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inst.size = opcode->size;
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(*opcode->parms) (p);
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@ -11706,6 +11882,7 @@ md_assemble (str)
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return;
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}
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mapping_state (MAP_ARM);
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inst.instruction = opcode->value;
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inst.size = INSN_SIZE;
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(*opcode->parms) (p);
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@ -12809,6 +12986,7 @@ s_arm_elf_cons (nbytes)
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md_cons_align (nbytes);
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#endif
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mapping_state (MAP_DATA);
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do
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{
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bfd_reloc_code_real_type reloc;
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@ -90,6 +90,9 @@ struct fix;
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#ifdef OBJ_ELF
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# define TARGET_FORMAT elf32_arm_target_format()
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extern const char * elf32_arm_target_format PARAMS ((void));
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# define md_elf_section_change_hook() arm_elf_change_section
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extern void arm_elf_change_section (void);
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#endif
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#define TC_FORCE_RELOCATION(FIX) arm_force_relocation (FIX)
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@ -22,6 +22,7 @@
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* ARM Floating Point:: Floating Point
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* ARM Directives:: ARM Machine Directives
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* ARM Opcodes:: Opcodes
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* ARM Mapping Symbols:: Mapping Symbols
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@end menu
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@node ARM Options
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@ -439,3 +440,32 @@ For information on the ARM or Thumb instruction sets, see @cite{ARM
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Software Development Toolkit Reference Manual}, Advanced RISC Machines
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Ltd.
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@node ARM Mapping Symbols
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@section Mapping Symbols
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The ARM ELF specification requires that special symbols be inserted
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into object files to mark certain features:
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@table @code
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@cindex @code{$a}
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@item $a
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At the start of a region of code containing ARM instructions.
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@cindex @code{$t}
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@item $t
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At the start of a region of code containing THUMB instructions.
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@cindex @code{$d}
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@item $d
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At the start of a region of data.
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@end table
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The assembler will automatically insert these symbols for you - there
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is no need to code them yourself. Support for tagging symbols ($b,
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$f, $p and $m) which is also mentioned in the current ARM ELF
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specification is not implemented. This is because they have been
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dropped from the new EABI and so tools cannot rely upon their
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presence.
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@ -1,3 +1,10 @@
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2003-11-13 Nick Clifton <nickc@redhat.com>
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* gas/arm/mapping.s: New test: Source for ARM ELF mapping
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symbols test.
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* gas/arm/mapping.d: New file: Expected output.
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* gas/arm/arm.exp: Run new test.
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2003-11-06 Nick Clifton <nickc@redhat.com>
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* gas/arm/req.s: New test file. Check .req and .unreq psuedo ops.
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@ -68,6 +68,8 @@ if {[istarget *arm*-*-*] || [istarget "xscale-*-*"]} then {
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if {[istarget *-*-elf*] || [istarget *-*-linux*]} then {
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run_dump_test "pic"
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run_dump_test "mapping"
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}
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gas_test "offset.s" "" $stdoptlist "OFFSET_IMM regression"
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18
gas/testsuite/gas/arm/mapping.d
Normal file
18
gas/testsuite/gas/arm/mapping.d
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@ -0,0 +1,18 @@
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#objdump: --syms
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#name: ARM Mapping Symbols
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# Test the generation of ARM ELF Mapping Symbols
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.*: +file format.*arm.*
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SYMBOL TABLE:
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0+00 l d .text 0+0
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0+00 l d .data 0+0
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0+00 l d .bss 0+0
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0+00 l F .text 0+0 \$a
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0+08 l .text 0+0 \$t
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0+00 l O .data 0+0 \$d
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0+00 l d foo 0+0
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0+00 l foo 0+0 \$t
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0+00 g .text 0+0 mapping
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0+08 g .text 0+0 thumb_mapping
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19
gas/testsuite/gas/arm/mapping.s
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19
gas/testsuite/gas/arm/mapping.s
Normal file
@ -0,0 +1,19 @@
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.text
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.arm
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.global mapping
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mapping:
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nop
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bl mapping
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.global thumb_mapping
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.thumb_func
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thumb_mapping:
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.thumb
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nop
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bl thumb_mapping
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.data
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.word 0x123456
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.section foo,"ax"
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nop
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