[PATCH] readelf: When highpc is in constant form also print as address.

Jan Kratochvil jan.kratochvil at redhat.com
Tue Mar 26 06:58:25 UTC 2013


On Mon, 25 Mar 2013 21:23:26 +0100, Mark Wielaard wrote:
> @@ -5437,7 +5438,19 @@ attr_callback (Dwarf_Attribute *attrp, void *arg)
>        if (cbargs->silent)
>  	break;
>  
> -      if (valuestr == NULL)
> +      /* When highpc is in constant form it is relative to lowpc.
> +	 In that case also show the address.  */
> +      Dwarf_Addr highpc;
> +      if (attr == DW_AT_high_pc && (dwarf_highpc (cbargs->die, &highpc) == 0))
> +	{
> +	  char *a = format_dwarf_addr (cbargs->dwflmod, cbargs->addrsize,
> +				       highpc - 1, highpc);

That "- 1" is a bug:

DWARF-4.0:
If the value of the DW_AT_high_pc is of class address, it is the relocated
address of the first location past the last instruction associated with the
entity; if it is of class constant, the value is an unsigned integer offset
which when added to the low PC gives the address of the first location past
the last instruction associated with the entity.

gcc/dwarf2out.c:
        case dw_val_class_high_pc:
          dw2_asm_output_delta (DWARF2_ADDR_SIZE, AT_lbl (a),
                                get_AT_low_pc (die), "DW_AT_high_pc");

gdb/dwarf2read.c:
          if (attr_high->form == DW_FORM_addr
              || attr_high->form == DW_FORM_GNU_addr_index)
            high = DW_ADDR (attr_high);
          else
            high = low + DW_UNSND (attr_high);

I see no + 1 or -1 there.

             low_pc               (addr) 0x0000000000400530 <main>
             high_pc              (data8) 32 (0x000000000040054f <main+0x1f>)

0000000000400530 <main>:
main():
  400530:       55                      push   %rbp
[...]
  40054e:       c9                      leaveq 
  40054f:       c3                      retq   
0000000000400550 <__libc_csu_init>:


vs. when build with FSF GCC 4.7:

             low_pc               (addr) 0x000000000040051c <main>
             high_pc              (addr) 0x000000000040053c

000000000040051c <main>:
  40051c:       55                      push   %rbp
[...]
  40053a:       c9                      leaveq 
  40053b:       c3                      retq   
  40053c:       0f 1f 40 00             nopl   0x0(%rax)



Thanks,
Jan


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