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

Simon Marchi via Gdb-patches
2021-01-28T15:52:04Z

On 2021-01-28 10:41 a.m., Zoran Zaric wrote:
>> 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

Note that an identical change was already merged:

https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=9f6c202e573b796a9e7328cc5fdab7c0c63776bf

So this patch will probably disappear when I rebase.

Simon