[PATCH] Fix crash with DW_FORM_implicit_const

[Andrew Burgess]

Tom Tromey <tom@tromey.com> writes:

> Jakub pointed out that using DW_FORM_implicit_const with
> DW_AT_bit_size would cause gdb to crash.  This happened because
> DW_FORM_implicit_const is not an "unsigned" form, causing as_unsigned
> to assert.  This patch fixes the problem.

LGTM.

Approved-By: Andrew Burgess <aburgess@redhat.com>

Thanks,
Andrew


>
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30651
> ---
>  gdb/dwarf2/read.c                    | 29 ++++++++++++++++------------
>  gdb/testsuite/gdb.dwarf2/intbits.exp |  2 +-
>  gdb/testsuite/lib/dwarf.exp          |  4 ++++
>  3 files changed, 22 insertions(+), 13 deletions(-)
>
> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
> index 3508f2c29ee..b1f1c1d7257 100644
> --- a/gdb/dwarf2/read.c
> +++ b/gdb/dwarf2/read.c
> @@ -15420,20 +15420,25 @@ read_base_type (struct die_info *die, struct dwarf2_cu *cu)
>    if (TYPE_SPECIFIC_FIELD (type) == TYPE_SPECIFIC_INT)
>      {
>        attr = dwarf2_attr (die, DW_AT_bit_size, cu);
> -      if (attr != nullptr && attr->as_unsigned () <= 8 * type->length ())
> +      if (attr != nullptr && attr->form_is_constant ())
>  	{
> -	  unsigned real_bit_size = attr->as_unsigned ();
> -	  attr = dwarf2_attr (die, DW_AT_data_bit_offset, cu);
> -	  /* Only use the attributes if they make sense together.  */
> -	  if (attr == nullptr
> -	      || (attr->as_unsigned () + real_bit_size
> -		  <= 8 * type->length ()))
> +	  unsigned real_bit_size = attr->constant_value (0);
> +	  if (real_bit_size >= 0 && real_bit_size <= 8 * type->length ())
>  	    {
> -	      TYPE_MAIN_TYPE (type)->type_specific.int_stuff.bit_size
> -		= real_bit_size;
> -	      if (attr != nullptr)
> -		TYPE_MAIN_TYPE (type)->type_specific.int_stuff.bit_offset
> -		  = attr->as_unsigned ();
> +	      attr = dwarf2_attr (die, DW_AT_data_bit_offset, cu);
> +	      /* Only use the attributes if they make sense together.  */
> +	      if (attr == nullptr
> +		  || (attr->form_is_constant ()
> +		      && attr->constant_value (0) >= 0
> +		      && (attr->constant_value (0) + real_bit_size
> +			  <= 8 * type->length ())))
> +		{
> +		  TYPE_MAIN_TYPE (type)->type_specific.int_stuff.bit_size
> +		    = real_bit_size;
> +		  if (attr != nullptr)
> +		    TYPE_MAIN_TYPE (type)->type_specific.int_stuff.bit_offset
> +		      = attr->constant_value (0);
> +		}
>  	    }
>  	}
>      }
> diff --git a/gdb/testsuite/gdb.dwarf2/intbits.exp b/gdb/testsuite/gdb.dwarf2/intbits.exp
> index c52e709316b..cf44d26b721 100644
> --- a/gdb/testsuite/gdb.dwarf2/intbits.exp
> +++ b/gdb/testsuite/gdb.dwarf2/intbits.exp
> @@ -43,7 +43,7 @@ Dwarf::assemble ${asm_file} {
>  		{DW_AT_endianity @DW_END_little}
>  		{DW_AT_name "i7"}
>  		{DW_AT_byte_size 2 DW_FORM_udata}
> -		{DW_AT_bit_size 7 DW_FORM_udata}
> +		{DW_AT_bit_size 7 DW_FORM_implicit_const}
>  	    }
>  
>  	    DW_TAG_variable {
> diff --git a/gdb/testsuite/lib/dwarf.exp b/gdb/testsuite/lib/dwarf.exp
> index 434495df24a..f09da0430ab 100644
> --- a/gdb/testsuite/lib/dwarf.exp
> +++ b/gdb/testsuite/lib/dwarf.exp
> @@ -693,6 +693,7 @@ namespace eval Dwarf {
>  		_op .ascii [_quote $value]
>  	    }
>  
> +	    DW_FORM_implicit_const -
>  	    DW_FORM_flag_present {
>  		# We don't need to emit anything.
>  	    }
> @@ -917,6 +918,9 @@ namespace eval Dwarf {
>  	    }
>  	    _op .uleb128 $_constants($attr_name) $attr_name
>  	    _op .uleb128 $_constants($attr_form) $attr_form_comment
> +	    if {$attr_form eq "DW_FORM_implicit_const"} {
> +		_op .sleb128 $attr_value "the constant"
> +	    }
>  	}
>      }
>  
> -- 
> 2.41.0