Hi,

This patch fixes two problems: the type of mapping symbols is made 
STT_NOTYPE (from STT_FUNC or STT_OBJECT from ARM/Thumb or data 
respectively), and the alignment is corrected to not have the low bit 
set for Thumb mapping symbols, in accordance with the latest version of 
the ARM AAELF spec.

Unfortunately altering the symbol type to STT_NOTYPE for mapping symbols 
affects the output of disassembly from objdump. $a and $t were 
previously treated as functions. When objdump tried to find the closest 
symbol for possibly-symbol-relative offsets previously, it found those 
mapping symbols since compare_symbols places functions first in a sorted 
version of the symbol table. They were then rejected by the 
symbol_is_valid hook (arm_symbol_is_valid) from the disassemble_info 
struct, and the section name was printed instead.

When the type of mapping symbols is changed to STT_NOTYPE, they are no 
longer placed first in the sorted symbol list, so another symbol is used 
instead. This causes test regressions, e.g. a symbol-offset address 
which was previously output as:

   bl      8224 <.text-0xc>

was output instead as:

   bl      8224 <_start-0xc>

In the interest of preserving existing behaviour, I have fixed this by 
adding a new disassemble_info hook which allows the symbol table used 
for disassembly to have a target-specific hook for altering each symbol 
(or remove it) in the remove_useless_symbols function. This sets the 
BSF_FUNCTION flag for mapping symbols, which makes things behave the way 
they used to, and possibly provides useful functionality for other 
platforms as well.

It may be better to just change the expected test output instead. Thoughts?

Tested on arm-none-eabi, arm-none-symbianelf, and i686-pc-linux-gnu with 
all targets.

OK to apply?

ChangeLog:

   * bfd/elf32-arm.c (arm_elf_find_function): include STT_NOTYPE in test
   for mapping symbols.
   * binutils/objdump.c (remove_useless_symbols): Add disassemble_info
   parameter, and call new hook to filter symbols in a target-specific
   way.
   (disassemble_data): Initialise sorted symbols after disassemble_info
   struct, and call remove_useless_symbols before sorting.
   * gas/config/tc-arm.c (mapping_state): Update documentation in
   function comment. Change type of all mapping symbols to BSF_NO_FLAGS.
   (is_mapping_symbol_name): New function.
   (arm_adjust_symtab): Don't adjust type of mapping symbols here.
   * gas/testsuite/gas/arm/mapping.d: Change expected output for untyped
   symbols.
   * include/dis-asm.h (disassemble_info): Add filter_symbol hook.
   (arm_filter_symbol): Add prototype.
   * opcodes/arm-dis.c (arm_filter_symbol): New function to add
   BSF_FUNCTION for code mapping symbols.
   * opcodes/dis-init.c (init_disassemble_info): Initialise filter_symbol
   hook (NULL).
   * opcodes/disassemble.c (disassemble_init_for_target): Initialise
   filter_symbol hook for ARM.