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

[Paolo Bonzini <pbonzini@redhat.com>]

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 *'.

Paolo