diff options
| -rw-r--r-- | HACKING | 19 |
1 files changed, 17 insertions, 2 deletions
@@ -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 |