Hi Peter, [+John/Richards/Paolo/Gueunter]
On 2/18/21 3:22 PM, Peter Maydell wrote: > On Thu, 18 Feb 2021 at 14:07, Bin Meng <[email protected]> wrote: >> On Thu, Feb 18, 2021 at 9:26 PM Peter Maydell <[email protected]> >> wrote: >>> Fails to compile, 32 bit hosts: >>> >>> ../../hw/riscv/virt.c: In function 'virt_machine_init': >>> ../../hw/riscv/virt.c:621:43: error: comparison is always false due to >>> limited range of data type [-Werror=type-limits] >>> if ((uint64_t)(machine->ram_size) > 10 * GiB) { >>> ^ >>> ../../hw/riscv/virt.c:623:33: error: large integer implicitly >>> truncated to unsigned type [-Werror=overflow] >>> machine->ram_size = 10 * GiB; >>> ^~ >> >> This kind of error is tricky. I wonder whether we should deprecate >> 32-bit host support though. > > 32-bit host is still not uncommon outside the x86 world... > > The thing that makes this particular check awkward is that > machine->ram_size is a ram_addr_t, whose size is 64 bits if > either (a) the host is 64 bits or (b) CONFIG_XEN_BACKEND is > enabled, so it's effectively only 32-bits on 32-bit-not-x86. > > It might be a good idea if we decided that we would just make > ram_addr_t 64-bits everywhere, to avoid this kind of "we > have an unusual config only on some more-obscure hosts" issue. > (We did that for hwaddr back in commit 4be403c8158e1 in 2012, > when it was still called target_phys_addr_t.) This change > would probably be a performance hit for 32-bit-non-x86 hosts; > it would be interesting to see whether it was measurably > significant. You once explained me we have 'hwaddr' (physical address) of 64-bit because we can 64-bit buses on 32-bit targets. hwaddr is available in all emulation modes. ram_addr_t is restricted to system emulation. I understand it as the limit addressable by a CPU. Back to your comment, we only have 32-bit ram_addr_t on system-emulation on 32-bit (non-x86) hosts. Question I asked yesterday on IRC, do you know if there is still interest in having system-emulation on 32-bit hosts? It is important to keep user-mode emulation on 32-bit hosts, but I doubt there are many uses of system-emulation on them (even less non non-x86 archs). Regards, Phil.
