Re: [PATCH 1/5] Code for nds32 target

[Yao Qi <yao@codesourcery.com>]

On 07/10/2013 02:23 AM, Wei-cheng Wang wrote:
>     Target description can not describe a enum-typed bit-field.
>
>     If bit-field struct is used, I could not specify the type for
>     a bit-field.
>
>       <struct id="id" size="size">
>         <field name="name" start="start" end="end"/>
>         ...
>       </struct>
>
>     If I want to specify field type, I couldn't specify size of a field.
>
>       <struct id="id">
>         <field name="name" type="type"/>
>         ...
>       </struct>
>

FAOD, this works in general.  See testsuite/gdb.xml/extra-regs.xml. 
However, TYPE can't be flags.  For example, I hack 'i386_eflags' in 
i386/32bit-core.xml, which splits eflags registers into three groups (or 
types),

   <flags id="i386_eflags_1" size="1">
     <field name="CF" start="0" end="0"/>
     <field name="" start="1" end="1"/>
     <field name="PF" start="2" end="2"/>
     <field name="AF" start="4" end="4"/>
     <field name="ZF" start="6" end="6"/>
     <field name="SF" start="7" end="7"/>
   </flags>

   <flags id="i386_eflags_2" size="1">
     <field name="TF" start="0" end="0"/>
     <field name="IF" start="1" end="1"/>
     <field name="DF" start="2" end="2"/>
     <field name="OF" start="3" end="3"/>
     <field name="NT" start="4" end="4"/>
   </flags>

   <flags id="i386_eflags_3" size="1">
     <field name="RF" start="0" end="0"/>
     <field name="VM" start="1" end="1"/>
     <field name="AC" start="2" end="2"/>
     <field name="VIF" start="3" end="3"/>
     <field name="VIP" start="4" end="4"/>
     <field name="ID" start="5" end="5"/>
   </flags>

   <struct id="i386_eflags" size="4">
     <field name="a" type="i386_eflags_1"/>
     <field name="b" type="i386_eflags_2"/>
     <field name="c" type="i386_eflags_3"/>
   </struct>

Then I get an error:

   Explicitly sized type can not contain non-bitfield "a"

It is a limitation of <struct> and <flags>, which was mentioned in the 
patch submission.

   [patch] Add support for <struct> and <flags> in target descriptions
   http://sourceware.org/ml/gdb-patches/2010-02/msg00542.html

I can't evaluate how much efforts are needed to fix this limitation.

>     All I want is to display a register in such format.
>
>       (gdb) p $cr0
>       $1 = {CFGID = [ PERF_EXT 16_EXT PERF_EXT2 COP_EXT STR_EXT ],
>       REV = 16, CPUID = N13}
>
>     (cr0 consist of config flags, revision number and CPU ID.)

With some hack (comment out the code which throws error) in 
xml-tdesc.c:tdesc_start_field, I can get something similar to yours,

(gdb) p $eflags
$1 = {a = [ SF ], b = [ IF ], c = [ ]}

Probably, it is what you want.  Looks target description is quite 
'friendly' to be extended, but I don't know what to start with or how 
much work is needed.

-- 
Yao (齐尧)