Re: [PATCH 3/5] fbsd-nat: Pass an optional register base to the register set helpers.

John Baldwin
2022-11-22T22:25:42Z

On 11/22/22 2:16 PM, John Baldwin wrote:
> On 11/22/22 12:38 PM, Simon Marchi wrote:
>> On 7/7/22 20:58, John Baldwin wrote:
>>> This is needed to permit using the helpers for register sets with a
>>> variable base. In particular regnum needs to be converted into a
>>> relative register number before passed to regcache_map_supplies.
>>> ---
>>> gdb/fbsd-nat.c | 34 +++++++++++++++++++---------------
>>> gdb/fbsd-nat.h | 49 ++++++++++++++++++++++++++++---------------------
>>> 2 files changed, 47 insertions(+), 36 deletions(-)
>>>
>>> diff --git a/gdb/fbsd-nat.c b/gdb/fbsd-nat.c
>>> index 9d7383ac0ab..edcd3fc3ed1 100644
>>> --- a/gdb/fbsd-nat.c
>>> +++ b/gdb/fbsd-nat.c
>>> @@ -1732,14 +1732,15 @@ fbsd_nat_target::supports_disable_randomization ()
>>> bool
>>> fbsd_nat_target::fetch_register_set (struct regcache *regcache, int regnum,
>>> int fetch_op, const struct regset *regset,
>>> - void *regs, size_t size)
>>> + int regbase, void *regs, size_t size)
>>> {
>>> const struct regcache_map_entry *map
>>> = (const struct regcache_map_entry *) regset->regmap;
>>> pid_t pid = get_ptrace_pid (regcache->ptid ());
>>>
>>> - if (regnum == -1 || regcache_map_supplies (map, regnum, regcache->arch(),
>>> - size))
>>> + if (regnum == -1
>>> + || (regnum >= regbase && regcache_map_supplies (map, regnum - regbase,
>>> + regcache->arch(), size)))
>>
>> My understanding is that it would be an internal error if the caller
>> passed a regnum that is < regbase. In order words, should you do:
>>
>> gdb_assert (regnum >= regbase);
>>
>> ?
>>
>> Actually, after reading the following patches, I think the answer is
>> no. When requesting a single register, we will still go through all the
>> fetch functions and we expect them to do nothing if the register is not
>> theirs. Leaving the question there in case others wonder about the same
>> thing.
>>
>> I was also wondering if it would be better to do the absolute ->
>> relative conversion in the caller. All this function knows is the
>> regset-relative view of things. In the end it doesn't matter much, it
>> just moves a condition from here to the callers. I'm fine with whatever
>> you prefer.
>
> If you do the adjustment to an absolute value in the caller you have to still
> special case for regnum == -1 when fetching all registers. The current approach
> here means that the special case for that is handled down in
> regcache:transfer_regset which already has a special case for -1.

Ah, I think I misunderstood your point. While I could perhaps push the
regcache_map_supplies check out to the callers, that would somewhat defeat the
point of these helpers which is to reduce duplicated code in callers.

--
John Baldwin