| Message ID | 20170529101413.GN16511@redhat.com |
|---|---|
| State | New |
| Headers | show |
On 29.05.2017 12:14, Richard W.M. Jones wrote: > 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 I guess you could also use "-march=i486" here instead, since QEMU does not emulate a 386, as far as I can see. Thomas
On 05/29/2017 05:14 AM, Richard W.M. Jones wrote: > 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. Is there any way to make it just _not_ load the option rom for -cpu 486? It ran fine before that thing went in... Rob
On 30.05.2017 21:05, Rob Landley wrote: > On 05/29/2017 05:14 AM, Richard W.M. Jones wrote: >> 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. > > Is there any way to make it just _not_ load the option rom for -cpu 486? > It ran fine before that thing went in... Looking at that commit b2a575a1c652 that you've mentioned, it seems like you could work-around the problem by disabling DMA for the fw_cfg device. Try something like adding the parameter -global fw_cfg.dma_enabled=false to your command line. If that does not help, try to use an older machine type, like "-M pc-i440fx-2.5". Thomas
On Tue, May 30, 2017 at 02:05:15PM -0500, Rob Landley wrote: > On 05/29/2017 05:14 AM, Richard W.M. Jones wrote: > > 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. > > Is there any way to make it just _not_ load the option rom for -cpu 486? > It ran fine before that thing went in... Well it ran, but it was very slow. The DMA method can be literally orders of magnitude faster. Does adding the flag I suggested help? Rich.
On 30/05/2017 21:05, Rob Landley wrote: > On 05/29/2017 05:14 AM, Richard W.M. Jones wrote: >> 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. > > Is there any way to make it just _not_ load the option rom for -cpu 486? > It ran fine before that thing went in... You were loading another option ROM. Thomas's suggested -global invocation will revert to that ROM until we fix it. Paolo
--- 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