[haiku-development] Re: RFC PCI config access API change
- From: Jérôme Duval <jerome.duval@xxxxxxxxx>
- To: haiku-development <haiku-development@xxxxxxxxxxxxx>
- Date: Mon, 24 Jun 2013 00:15:01 +0200
2013/6/23 Axel Dörfler <axeld@xxxxxxxxxxxxxxxx>:
> On 06/21/2013 09:18 PM, Jérôme Duval wrote:
>>
>> For compatibility, we could also introduce a new bus_managers/pci/v2
>> interface, or extend the current with new functions.
>> A function find_pci_extended_capability would be added anyway.
>
>
> I may be mistaken, but AFAIR this change should not hurt compatibility, as
> the arguments are usually 4 bytes large in any case. It might hurt as there
> is no requirement that the upper bits are cleared, but I don't know how GCC2
> handles this case.
Here is what happens on a call in GCC2:
3582a: 6a 02 push $0x2
3582c: 6a 06 push $0x6
3582e: 31 c0 xor %eax,%eax
35830: 8a 46 06 mov 0x6(%esi),%al
35833: 50 push %eax
35834: 31 c0 xor %eax,%eax
35836: 8a 46 05 mov 0x5(%esi),%al
35839: 50 push %eax
3583a: 31 c0 xor %eax,%eax
3583c: 8a 46 04 mov 0x4(%esi),%al
3583f: 50 push %eax
35840: e8 f3 b0 ff ff call 30938 <pci_read_config>
then
00030938 <pci_read_config>:
30938: 55 push %ebp
30939: 89 e5 mov %esp,%ebp
3093b: 83 ec 14 sub $0x14,%esp
3093e: 53 push %ebx
3093f: e8 00 00 00 00 call 30944 <pci_read_config+0xc>
30944: 5b pop %ebx
30945: 81 c3 f8 e4 08 00 add $0x8e4f8,%ebx
3094b: 8a 45 0c mov 0xc(%ebp),%al
3094e: 88 45 f7 mov %al,-0x9(%ebp)
30951: 8a 45 10 mov 0x10(%ebp),%al
30954: 88 45 f6 mov %al,-0xa(%ebp)
30957: 8a 45 14 mov 0x14(%ebp),%al
3095a: 88 45 f5 mov %al,-0xb(%ebp)
3095d: 8a 45 18 mov 0x18(%ebp),%al
30960: 88 45 f4 mov %al,-0xc(%ebp)
Arguments are in fact 4 bytes large anyway, the question is as you
evoke how many bytes are written by a push byte operation. From the
IA32 doc, it would be at least 2 (a word or a double word).
>
> Other than that, I wouldn't mind either way you outlined above :-)
OK
Bye,
Jérôme
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