From 2be8d4509896116dae7b3b9dffc0fccef480126d Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Mon, 22 Jul 2013 18:34:35 +0200 Subject: HACKING: Document vaddr type usage MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Also extend documentation of target_ulong and abi_ulong. Signed-off-by: Peter Maydell Signed-off-by: Andreas Färber --- HACKING | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) (limited to 'HACKING') diff --git a/HACKING b/HACKING index e73ac79fe9..12fbc8afe4 100644 --- a/HACKING +++ b/HACKING @@ -40,8 +40,23 @@ speaking, the size of guest memory can always fit into ram_addr_t but it would not be correct to store an actual guest physical address in a ram_addr_t. -Use target_ulong (or abi_ulong) for CPU virtual addresses, however -devices should not need to use target_ulong. +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. 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. Of course, take all of the above with a grain of salt. If you're about to use some system interface that requires a type like size_t, pid_t or -- cgit v1.2.1