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Re: [Qemu-devel] Commit b2a575a1c652 broke i486 support.
From: |
Richard W.M. Jones |
Subject: |
Re: [Qemu-devel] Commit b2a575a1c652 broke i486 support. |
Date: |
Mon, 29 May 2017 11:14:13 +0100 |
User-agent: |
Mutt/1.5.20 (2009-12-10) |
On Mon, May 29, 2017 at 11:22:14AM +0200, Thomas Huth wrote:
> On 28.05.2017 07:18, Rob Landley wrote:
> > You can't boot a kernel under -cpu 486 since that commit (hangs
> > producing no output) because it added a bios image that won't run on
> > anything short of pentium II.
> >
> > You can try the run-emulator.sh script in
> > http://landley.net/aboriginal/downloads/binaries/system-image-i486.tar.gz
> > before and after that commit to check for yourself.
>
> Hi Rob,
>
> thanks for the bug report ... but to make sure that your mail does not
> get lost in the high traffic of the qemu-devel mailing list, it might be
> a good idea to CC: the people from that commit b2a575a1c652 in this case
> (which I've done now).
I see in the disassembly use of cmovne (new in Pentium Pro) and
bswap (new in 486).
[http://cse.unl.edu/~goddard/Courses/CSCE351/IntelArchitecture/InstructionSetSummary.pdf]
The cmovne instruction is generated by the compiler (GCC in my case),
The following patch removes the cmovne instruction, so it should work
on 486 (although I didn't test it). It's not possible to remove bswap
without surgery on the inline assembler.
--- a/pc-bios/optionrom/Makefile
+++ b/pc-bios/optionrom/Makefile
@@ -13,6 +13,7 @@ $(call set-vpath, $(SRC_PATH)/pc-bios/optionrom)
ifeq ($(lastword $(filter -O%, -O0 $(CFLAGS))),-O0)
override CFLAGS += -O2
endif
+override CFLAGS += -march=i386
# Drop -fstack-protector and the like
QEMU_CFLAGS := $(filter -W%, $(QEMU_CFLAGS)) $(CFLAGS_NOPIE) -ffreestanding
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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- [Qemu-devel] Commit b2a575a1c652 broke i486 support., Rob Landley, 2017/05/28
- Re: [Qemu-devel] Commit b2a575a1c652 broke i486 support., Thomas Huth, 2017/05/29
- Re: [Qemu-devel] Commit b2a575a1c652 broke i486 support.,
Richard W.M. Jones <=
- Re: [Qemu-devel] Commit b2a575a1c652 broke i486 support., Thomas Huth, 2017/05/29
- Re: [Qemu-devel] Commit b2a575a1c652 broke i486 support., Rob Landley, 2017/05/30
- Re: [Qemu-devel] Commit b2a575a1c652 broke i486 support., Thomas Huth, 2017/05/31
- Re: [Qemu-devel] Commit b2a575a1c652 broke i486 support., Richard W.M. Jones, 2017/05/31
- Re: [Qemu-devel] Commit b2a575a1c652 broke i486 support., Paolo Bonzini, 2017/05/31