Re: [Qemu-devel] [PATCH qom-cpu] HACKING: Document vaddr type usage

["Andreas Färber" <afaerber@suse.de>]

Am 23.07.2013 08:33, schrieb Paolo Bonzini:
> Il 22/07/2013 19:27, Peter Maydell ha scritto:
>> On 22 July 2013 17:36, Andreas Färber <afaerber@suse.de> wrote:
>>> Signed-off-by: Andreas Färber <afaerber@suse.de>
>>> ---
>>>  HACKING | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/HACKING b/HACKING
>>> index e73ac79..d9dbb46 100644
>>> --- a/HACKING
>>> +++ b/HACKING
>>> @@ -42,6 +42,7 @@ ram_addr_t.
>>>
>>>  Use target_ulong (or abi_ulong) for CPU virtual addresses, however
>>>  devices should not need to use target_ulong.
>>> +Use vaddr for CPU virtual addresses in target-independent code.
>>
>> Here's my suggestion for this paragraph (ie to replace
>> both the "Use target_ulong..." and "Use vaddr" sentences
>> above):
>>
>> ===begin===
>> For CPU virtual addresses there are several possible types.
>> vaddr is the best type to use to hold a CPU virtual address
>> in target-independent code, including most devices. It is
>> guaranteed to be large enough to hold a virtual address for
>> any target, and it does not change size from target to target.
>> It is always unsigned.
>> target_ulong is a type the size of a virtual address on the CPU;
>> this means it may be 32 or 64 bits depending on which target
>> is being built. It should therefore be used only in target
>> specific code, and in some performance-critical built-per-target
>> core code such as the TLB code. There is also a signed version,
>> target_long.
>> abi_ulong is for the *-user targets, and represents a type the
>> size of 'void *' in that target's ABI. (This may not be the same
>> as the size of a full CPU virtual address in the case of target
>> ABIs which use 32 bit pointers on 64 bit CPUs, like sparc32plus.)
>> Definitions of structures that must match the target's ABI
>> must use this type for anything that on the target is defined
>> to be an 'unsigned long' or a pointer type. There is also a
>> signed version, abi_long.
>> ===endit===
>>
>> (cc'ing Paolo to check I didn't mangle the abi_ulong/target_ulong
>> distinction.)
> 
> Yes, it's fine.  You might add that abi_short, abi_int, etc. also exist,
> and that they have the same alignment as short/int/etc in the target ABI.
> 
> There is one nit: tn fact abi_ulong has the size of 'long'---which is
> the same as 'void *', but only because our *-user targets are all ILP32
> or LP64.  A hypotectical windows-user target would make abi_ullong the
> size of 'void *'.

Given the number of people that will read HACKING to that detail level,
I hope you can send a follow-up patch to clarify that once merged. :)

Andreas

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