On 8/3/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote:
> Hi Aubrey,
> Aubrey Li wrote:
> > On 8/2/07, Gavin Maltby <[EMAIL PROTECTED]> wrote:
> >
> >> On 08/02/07 14:18, Aubrey Li wrote:
> >>
> >>> Hi all,
> >>>
> >>> I can access a Global structure by mdb-> Global_struct=X, it prints
> >>> the address of that structure. Now I want to access it from user
> >>> space, so I wrote a driver and put it in the read op.
> >>> cmn_err(CE_NOTE, "Global structure = 0x%x\n", (unsigned
> >>> int)&Global_struct);
> >>>
> >>> The driver build successful but report error( undefined symbol) when
> >>> issue "add_drv mydriver".
> >>> It's wired for me. Can't the driver access the global variable of the
> >>> kernel?
> >>>
> >> Yes there are restrictions.
> >>
> >> The 'mem' driver already exists for this purpose - it supplies /dev/zero,
> >> /dev/mem, /dev/physmem, /dev/kmem, /dev/allkmem etc. Together with
> >> /dev/ksyms (see manpage) they provide the infrastructure on top
> >> of which libkvm builds, and mdb just uses those interfaces.
> >> So you can lookup a symbol or symbols using kvm_nlist and then
> >> read out the structure with kvm_read. Those are supplied
> >> by libkvm and you can use that to build standalone applications.
> >> Alternatively, work within the friendlier mdb api but accept
> >> living in a dcmd or walker.
> >>
> >> Cheers
> >>
> >> Gavin
> >>
> >>
> >>
> > Hi Gavin,
> >
> > Thanks for your quick reply.
> > I don't think a standalone application is my purpose, but I'm not
> > familiar with kvm_read.
> > I wanna dump a kernel global structure from user space, even using
> > kvm_read, I think I can only get an address? So I need type-casting to
> > convert the address to an structure pointer, here I need the structure
> > define, where kernel header is needed.
> > So Is the driver still a better choice?
> >
> Once you have the address (from the driver cmn_err() call), you could
> just open /dev/kmem, lseek to the address, and print the contents of the
> structure, something like:
>
> fd = open("/dev/kmem", O_RDONLY);
> lseek(fd, kernel_address, SEEK_SET);
> read(fd, &global_structure, sizeof(global_structure));
> printf("xxx = %x\n", global_structure.xxx);
> printf("yyy = %x\n", global_structure.yyy);
Here, global_structure is defined in the kernel head file, and this
file depends on another bunch of head files, How could access it in a
standalone program?
> ...
>
> Instead of printing the global address from the driver, you could
> instead add an ioctl to get the address, and then
> have you app open the device, ioctl to get the address, and then do the
> above. Really, if all you want to do
> is print the structure from user space, it would be much simpler to use
> mdb to do this. mdb is in user space.
Yes, mdb can dump the root node of the structure, while the whole
structure is a tree, I need the info of every nodes. So, mdb is not
enough.
>
> Also, the driver can access global variables. If you are getting an
> "undefined symbol" when you try to load the
> driver, it sounds like the global symbol is defined in some other module
> (driver), and the module/driver where the
> symbol is defined is not loaded when the driver is being added. When
Firstly, The command "global_struct=X" can print the address of this variable.
I think that means is already loaded. Then I run "add_drv" command to
add my driver.
It still reports "undefined symbol".
> you build the driver, use:
> $ ld -r -dy -N drv/foo mydriver.o -o mydriver
>
> to specify that your driver (mydriver) has a dependency on the "foo"
> module (where "foo" defines the global).
I'll have a try, thanks for your help, ;-)
-Aubrey
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