Re: [PATCH] gdb: specify sh4al-dsp register types

["Sébastien Michelland" <sebastien.michelland@lcis.grenoble-inp.fr>]

On 2024-04-01 05:25, Simon Marchi wrote:
> On 2024-03-31 18:26, Sébastien Michelland wrote:
>> This avoids $pc and similar registers being interpreted as negative when
>> in the upper half of the address space (e.g. by x/i), which doesn't
>> interact well with Xfer memory maps.
>> ---
>>
>> Hi,
>>
>> This patch fixes a pretty funny issue for the sh4al-dsp resulting from
>> $pc being typed as an int. When $pc is in the upper half of the address
>> space, `x/i $pc' would resolve to a negative value. At least in the case
>> of a remote target with an Xfer memory map, this leads to a spurious
>> "cannot access memory" error as negative addresses are out of bounds.
>>
>> (gdb) x/i $pc
>>     0x8c202c04:	Cannot access memory at address 0x8c202c04
>> (gdb) x/i 0x8c202c04
>> => 0x8c202c04 <gintctl_gint_gdb+304>:	mov.l	@r1,r10
>>
>> Affected registers are pc, pr (return address of a call), gbr (base
>> register for some specific addressing modes), vbr (interrupt handler)
>> and spc (return address after interrupt).
>>
>> It's not immediately clear to me why existing sh variants don't also do
>> that. Maybe it should be considered an issue with the memory map, or
>> maybe it's just a rare enough condition to not care.
> 
> Hi Sébastien,
> 
> I would suggest including all that info in the commit message proper.
> If I were to do some git-blaming and fall on that commit, I would
> appreciate having all that info right there.
> 
> I checked a few other arches, and it seems customary for arches to
> indicate that the PC register and some others should be typed as a
> builtin_func_ptr (while the SP register and some others should be typed
> as a builtin_data_ptr).  The fact that the sh arch doesn't do it seems
> like an oversight.
> 
> Another effect of having the pc typed as an int is that printing it will
> show it as a decimal, without symbol resolution.

Hi Simon, thanks for checking this patch.

I didn't think much of it but I do also get the decimal printing.

> If you want to try to fix the behavior on all sh arches, feel free to do
> so.  But otherwise, the patch LGTM:
> 
> Approved-By: Simon Marchi <simon.marchi@efficios.com>
> 
> Let me know if you don't have push access and would like me to push it
> for you.

I'll submit a v2 to get that same behavior on all sh arches--it feels 
better to have a consistent interpretation.

I indeed don't have push access, thanks for your help.

Sébastien