On 08/13/2012 04:41 PM, Markus Armbruster wrote: > Avi Kivity <a...@redhat.com> writes: > >> On 08/08/2012 12:04 PM, Markus Armbruster wrote: >>>> >>>> Yes please, maybe with a notice to the user. >>> >>> Next problem: minimum RAM size. >>> >>> For instance, -M pc -m X, where X < 32KiB dies "qemu: fatal: Trying to >>> execute code outside RAM or ROM at [...] Aborted (core dumped)" with >>> TCG, and "KVM internal error. Suberror: 1" with KVM. >>> >>> Should a minimum RAM size be enforced? Board-specific? >>> >> >> It's really a BIOS bug causing a limitation of both kvm and tcg to be >> hit. The BIOS should recognize it doesn't have sufficient memory and >> hang gracefully (if you can picture that). It just assumes some low >> memory is available and tries to execute it with the results you got. > > SeaBIOS indeed assumes it got at least 1MiB of RAM. It doesn't bother > to check CMOS for a smaller RAM size. However, that bug / feature is > currently masked by a QEMU bug: we screw up CMOS contents when there's > less than 1 MiB of RAM. pc_cmos_init(): > > int val, nb, i; > [...] > /* memory size */ > val = 640; /* base memory in K */ > rtc_set_memory(s, 0x15, val); > rtc_set_memory(s, 0x16, val >> 8); > > val = (ram_size / 1024) - 1024; > if (val > 65535) > val = 65535; > rtc_set_memory(s, 0x17, val); > rtc_set_memory(s, 0x18, val >> 8); > > If ram_size < 1MiB, val goes negative. Oops. > > For instance, with -m 500k, we happily promise 640KiB base memory (CMOS > addr 0x15..16), almost 64MiB extended memory (0x17..18 and 0x30..31), > yet no memory above 16MiB (0x34..35). > > An easy way to fix this is to require 1MiB of RAM :) > > But if you like, I'll put sane values in CMOS instead. That'll expose > the SeaBIOS bug.
IMO we need to fix CMOS reporting. (technically we shouldn't touch CMOS NVRAM at all; seabios should discover memory size via fwcfg and program it itself. But it's pointless to change it now) -- error compiling committee.c: too many arguments to function
