[Qemu-devel] qemu minimum memory requirements

[Darren Hart]

I'm trying to boot a fairly minimal x86 kernel image (5M uncompressed) with a
small (11M) busybox rootfs in qemu with a minimum amount of memory. I'm able to
reduce the memory available to qemu down to 21M and boot successfully, but below
that, I get the following:

$
/home/dvhart/source/poky.git/build-qemux86/tmp/sysroots/x86_64-linux/usr/bin/qemu
 -kernel 
/home/dvhart/source/poky.git/build-qemux86/tmp/deploy/images/bzImage-qemux86.bin
 -hda 
/home/dvhart/source/poky.git/build-qemux86/tmp/deploy/images/core-image-minimal-qemux86.ext3
 -m 20 --append "root=/dev/hda rw"
qemu: fatal: Trying to execute code outside RAM or ROM at 0x014284ec

EAX=014284ec EBX=01221000 ECX=00000000 EDX=00000000
ESI=00000000 EDI=01220ffc EBP=00100000 ESP=01431fc0
EIP=014284ec EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0018 00000000 ffffffff 00cf9300 DPL=0 DS   [-WA]
CS =0010 00000000 ffffffff 00cf9b00 DPL=0 CS32 [-RA]
SS =0018 00000000 ffffffff 00cf9300 DPL=0 DS   [-WA]
DS =0018 00000000 ffffffff 00cf9300 DPL=0 DS   [-WA]
FS =0018 00000000 ffffffff 00cf9300 DPL=0 DS   [-WA]
GS =0018 00000000 ffffffff 00cf9300 DPL=0 DS   [-WA]
LDT=0000 00000000 00000000 00008200 DPL=0 LDT
TR =0020 00001000 00000067 00008900 DPL=0 TSS32-avl
GDT=     00012fd0 00000027
IDT=     00000000 00000000
CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
DR0=00000000 DR1=00000000 DR2=00000000 DR3=00000000
DR6=ffff0ff0 DR7=00000400
CCS=00105fe0 CCD=00082ff0 CCO=SARL
EFER=0000000000000000
FCW=037f FSW=0000 [ST=0] FTW=00 MXCSR=00001f80
FPR0=0000000000000000 0000 FPR1=0000000000000000 0000
FPR2=0000000000000000 0000 FPR3=0000000000000000 0000
FPR4=0000000000000000 0000 FPR5=0000000000000000 0000
FPR6=0000000000000000 0000 FPR7=0000000000000000 0000
XMM00=00000000000000000000000000000000
XMM01=00000000000000000000000000000000
XMM02=00000000000000000000000000000000
XMM03=00000000000000000000000000000000
XMM04=00000000000000000000000000000000
XMM05=00000000000000000000000000000000
XMM06=00000000000000000000000000000000
XMM07=00000000000000000000000000000000
Aborted

I get similar results using the native qemu or kvm commands from my x86_64
Ubuntu 10.10 installation. The qemu console doesn't display anything past the
SeaBIOS version, so I'm wondering if this is unrelated to the kernel image and
simply a limitation of qemu and/or SeaBIOS.

Does anyone have some experience working with qemu with < 20M of memory?  I'm
trying to get to the point where I can boot in 8M of memory.

Thanks!

-- 
Darren Hart
Intel Open Source Technology Center
Yocto Project - Linux Kernel