debug info breaks build (Was: Re: Variable tracking (location lists support) - part 2)

[Joern Rennecke <joern dot rennecke at superh dot com>]

The addition of location list support broke sh-elf and sh64-elf builds.
Presumably all targets with a non-empty USTER_LABEL_PREFIX and dwarf2
debugging information are affected.

The new .debug_loc section contains invalid differences:

.Letext0:
        .section        .debug_loc,"",@progbits
.Ldebug_loc0:
.LLST0:
        .ualong 0xffffffff
        .ualong _.text
        .ualong .LVL0-_.text
        .ualong .LVL2-_.text

This is from the assembly file generated for muldi3 for sh-elf.

Here is a backtrace from the generation of the first invalid difference:

#0  dw2_assemble_integer (size=4, x=0x402aa3c0)
    at ../../srcw/gcc/dwarf2asm.c:50
#1  0x080e4c3f in dw2_asm_output_delta (size=4, lab1=0x83f7418 "*.LVL0", 
    lab2=0x830c42d ".text", 
    comment=0x830c4c0 "Location list begin address (%s)")
    at ../../srcw/gcc/dwarf2asm.c:107
#2  0x080ef71f in output_loc_list (list_head=0x4028be10)
    at ../../srcw/gcc/dwarf2out.c:6661
#3  0x080ee8cf in output_location_lists (die=0x40298b00)
    at ../../srcw/gcc/dwarf2out.c:6168
#4  0x080ee8ff in output_location_lists (die=0x40298ac0)
    at ../../srcw/gcc/dwarf2out.c:6171
#5  0x080ee8ff in output_location_lists (die=0x402097c0)
    at ../../srcw/gcc/dwarf2out.c:6171
#6  0x080ff38d in dwarf2out_finish (
    filename=0x83ee7b0 "../../srcw/gcc/libgcc2.c")
    at ../../srcw/gcc/dwarf2out.c:13439
#7  0x0824f52e in compile_file () at ../../srcw/gcc/toplev.c:1858
#8  0x08254bcc in do_compile () at ../../srcw/gcc/toplev.c:4678
#9  0x08254c62 in toplev_main (argc=19, argv=0xbfffe324)
    at ../../srcw/gcc/toplev.c:4718
#10 0x4004f507 in __libc_start_main (main=0x809e594 <main>, argc=19, 
    ubp_av=0xbfffe324, init=0x80494a0 <_init>, fini=0x82f7180 <_fini>, 
    rtld_fini=0x4000dc14 <_dl_fini>, stack_end=0xbfffe31c)
    at ../sysdeps/generic/libc-start.c:129

AFAIKS the basic problem is that curr->section is used like a label in
output_loc_list, which has been introduced in Daniel Berlin's patch from
2001-05-18 (dwarf2out.c version 1.270), but this code has not been used
during sh-elf or sh64-elf builds before.

The current form of this code is:

  if (strcmp (curr->section, ".text") == 0)
    {
      /* dw2_asm_output_data will mask off any extra bits in the ~0.  */
      dw2_asm_output_data (DWARF2_ADDR_SIZE, ~(unsigned HOST_WIDE_INT) 0,
                           "Location list base address specifier fake entry");
      dw2_asm_output_offset (DWARF2_ADDR_SIZE, curr->section,
                             "Location list base address specifier base");
    }

  /* Walk the location list, and output each range + expression.  */
  for (curr = list_head; curr != NULL; curr = curr->dw_loc_next)
    {
      unsigned long size;
      if (separate_line_info_table_in_use == 0)
        {
          dw2_asm_output_delta (DWARF2_ADDR_SIZE, curr->begin, curr->section,
                                "Location list begin address (%s)",
                                list_head->ll_symbol);
          dw2_asm_output_delta (DWARF2_ADDR_SIZE, curr->end, curr->section,
                                "Location list end address (%s)",
                                list_head->ll_symbol);
        }

curr->section is ".text"  Since there is no leading '*', LOCAL_LABEL_PREFIX
gets applied, so that we end up with _.text .