Re: [PATCH 07/13] gdb/dwarf: read DW_AT_ranges value as unsigned in partial_die_info::read

Zoran Zaric via Gdb-patches
2021-01-28T15:41:34Z

> From: Simon Marchi <simon.marchi@efficios.com>
>
> While writing a test for this series, I made a function
> (DW_AT_subprogram) with a DW_AT_ranges attribute using the
> DW_FORM_rnglistx form:
>
> 0x00000012: DW_TAG_subprogram
> DW_AT_name [DW_FORM_string] ("foo")
> DW_AT_ranges [DW_FORM_rnglistx] (indexed (0x0) rangelist = 0x00000036
> [0x0000000000004000, 0x0000000000005000))
>
> And strangely I couldn't print it:
>
> (gdb) p foo
> No symbol "foo" in current context.
>
> This is because of the `attr.constant_value (0)` in the DW_AT_ranges
> handling of partial_die_info::read. Since DW_FORM_rnglistx is not
> recognized as a constant value by attribute::constant_value, the default
> value (0) is returned. Down the line, this causes
> dwarf2_rnglists_process to try read a range list at offset 0 in the
> .debug_rnglists section, which is obviously wrong. In the end, no
> symbol is created for foo because we didn't find an address range.
>
> Use attr->as_unsigned instead. This is what is done for the equivalent
> code in dwarf2_get_pc_bounds. With this, GDB processes the subprogram
> DIE and we are able to print the function symbol:
>
> (gdb) p foo
> $1 = {void (void)} 0x4000
>
> Note that I didn't see an actual compiler use DW_FORM_rnglistx for a
> subprogram's range. However, in the binary attached to PR 26813, there
> are some lexical blocks with it:
>
> 0x0000d34a: DW_TAG_lexical_block
> DW_AT_ranges [DW_FORM_rnglistx] (indexed (0x2) rangelist = 0x000000d4
> [0x0000000000005db1, 0x0000000000005e36)
> [0x0000000000005e48, 0x0000000000005f3c)
> [0x0000000000006045, 0x0000000000006053))
>
> Their ranges are read incorrectly just like the ranges of the
> subprograms. With this patch applied, they are read correctly.
>

Good find.

Zoran