Re: [Qemu-devel] [PATCH] Bug Fix:Segmentation fault when use usb-ehci device

[Mike Qiu]

于 2013/7/19 22:32, Peter Maydell 写道:
> On 19 July 2013 15:12, Andreas Färber <address@hidden> wrote:
> > No, I don't. There were other segfault avoidance patches like yours over
> > the past months - they're all fixing individual segfault symptoms.
> > Question for Paolo is whether we want to continue to discover them one
> > by one or whether to implement a fallback inside memory code if .read or
> > .write is NULL.
> I think that the correct behaviour is "if neither
> .read nor .oldmmio.read[x] are set then behave as if
> .valid.accepts returned false" (ie "device has not responded
> to the read access, bus error").
>
> That said, if we want to add do-nothing functions instead,
> then (a) having memory.c provide a single set of nop functions
> that devices can use would be nicer than lots of individual
> nop functions and (b) a list to start with:
Yes, can we add one step in
memory_region_oldmmio_read_accessor() and
memory_region_oldmmio_write_accessor()
to check if the oldmmio read and write has been implement,
if no, for .write function, we just drop and do nothing,
for .read function, we drop read and return the value param
with 0xFF or other to show read fault.

Thus, we do not need to fix the segment fault in special field.

Thanks
Mike
> $ for f in $(find . -name '*.c'); do perl -e '$s = 0; while (<>) { if
> (/MemoryRegionOps (.*) =/) { $n = $1; $s = 1; next; } next if $s == 0;
> if (/\.read = /) { $s |= 2; } if (/\.write = /) { $s |= 4; } if (/;/)
> { print "$ARGV: $n: missing read\n" unless $s & 2; print "$ARGV: $n:
> missing write\n" unless $s & 4; $s = 0; }}' $f; done
> ./memory.c: unassigned_mem_ops: missing read
> ./memory.c: unassigned_mem_ops: missing write
> ./exec.c: notdirty_mem_ops: missing read
> ./hw/pci-host/prep.c: PPC_intack_ops: missing write
> ./hw/ssi/xilinx_spips.c: lqspi_ops: missing write
> ./hw/arm/omap1.c: omap_pwt_ops: missing read
> ./hw/arm/musicpal.c: mv88w8618_wlan_ops: missing write
> ./hw/scsi/megasas.c: megasas_queue_ops: missing write
> ./hw/usb/hcd-ehci.c: ehci_mmio_caps_ops: missing write
> ./hw/usb/hcd-uhci.c: uhci_ioport_ops: missing read
> ./hw/intc/openpic_kvm.c: kvm_openpic_mem_ops: missing read
> ./hw/intc/openpic.c: openpic_glb_ops_le: missing read
> ./hw/intc/openpic.c: openpic_glb_ops_be: missing read
> ./hw/intc/openpic.c: openpic_tmr_ops_le: missing read
> ./hw/intc/openpic.c: openpic_tmr_ops_be: missing read
> ./hw/intc/openpic.c: openpic_cpu_ops_le: missing read
> ./hw/intc/openpic.c: openpic_cpu_ops_be: missing read
> ./hw/intc/openpic.c: openpic_src_ops_le: missing read
> ./hw/intc/openpic.c: openpic_src_ops_be: missing read
> ./hw/pci/msix.c: msix_pba_mmio_ops: missing write
> ./hw/xen/xen_platform.c: xen_pci_io_ops: missing read
> ./hw/misc/lm32_sys.c: sys_ops: missing read
> ./hw/misc/pc-testdev.c: test_irq_ops: missing read
> ./hw/misc/pc-testdev.c: test_flush_ops: missing read
> ./hw/misc/vfio.c: vfio_ati_3c3_quirk: missing write
> ./hw/misc/debugexit.c: debug_exit_ops: missing read
> ./hw/net/lan9118.c: *mem_ops: missing read
> ./hw/net/lan9118.c: *mem_ops: missing write
> ./hw/char/grlib_apbuart.c: grlib_apbuart_ops: missing read
> ./hw/char/grlib_apbuart.c: grlib_apbuart_ops: missing write
> ./hw/isa/pc87312.c: pc87312_io_ops: missing read
> ./hw/nvram/fw_cfg.c: fw_cfg_ctl_mem_ops: missing read
>
> No doubt there are some false positives in there (eg fw_cfg.c
> provides a valid function so we'll never try to do reads)
> and it may miss some.
>
> -- PMM