Are pretend arguments included in the outgoing argument region ?

Jeff Law law@redhat.com
Wed Aug 14 17:09:00 GMT 2019


On 8/14/19 1:08 AM, Segher Boessenkool wrote:
> On Tue, Aug 13, 2019 at 10:32:27PM -0500, William Tambe wrote:
>> On Tue, Aug 13, 2019 at 9:44 PM Jeff Law <law@redhat.com> wrote:
>>>
>>> On 8/13/19 7:41 PM, William Tambe wrote:
>>>> Are pretend arguments included in the outgoing argument region ?
>>>> In other words, when ACCUMULATE_OUTGOING_ARGS is nonzero, does
>>>> crtl->outgoing_args_size include crtl->args.pretend_args_size ?
>>>>
>>> I think it varies depending on the target's ABI.
>>> OUTGOING_REG_PARM_STACK_SPACE, STACK_PARMS_IN_REG_PARM_AREA,
>>> REG_PARM_STACK_SPACE, etc likely come into play here.
>>>
>>> It may be better for you to describe the ABI you're working with.
>>> There's a reasonable chance it'll line up with an existing port's ABI
>>> and you can crib from that existing port.  Make sure to describe how
>>> varargs/stdarg is supposed to work, whether or not you have arguments
>>> passed partially in registers and partially in memory,
>>
>> The ABI I am working with pass arguments through registers where
>> NUM_ARG_REGS is the number of registers used to pass arguments.
>>
>> Given the following #define, is it enough to assume that pretend
>> arguments will be included in the outgoing argument region and that
>> crtl->outgoing_args_size will include crtl->args.pretend_args_size ?
>>
>> #define ACCUMULATE_OUTGOING_ARGS 1
>> #define REG_PARM_STACK_SPACE(F) (NUM_ARG_REGS*UNITS_PER_WORD)
>> #define OUTGOING_REG_PARM_STACK_SPACE(FNTYPE) 1
>> #define STACK_PARMS_IN_REG_PARM_AREA
> 
> Given your description, should you define any of the REG_PARM macros
> at all?  *Is* there an "outgoing argument region" in your ABI, if all
> args are passed in registers?
Right.  And how does stdarg/varargs work?  In particular what does the
callee do with register parameters if the callee is a varargs/stdarg
function?  Some will pull parameters from registers, others flush the
registers back to the stack in a args flushback area).  It's important.

jeff



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