[Xen-devel] RE: GDB and exec mode on xen

["Tan, Nicholas" <Nicholas.Tan@xxxxxxxxxx>]

Clarification:

 

I’m currently running a 64-bit linux kernel and am trying to connect to a 32-bit guest domain through xen, but I keep getting an issue where gdbserver seems to be sign extending a 32bit address into a 64bit one.

 

(gdb) bt

#0  0x00002b7ee48a6b03 in map_domain_va (xc_handle=6, cpu=0, guest_va=0xffffffff80107000, perm=1) at xc_ptrace.c:384

#1  0x00002b7ee48a6f79 in xc_ptrace (xc_handle=6, request=PTRACE_PEEKTEXT, domid_tid=0, eaddr=-2146406400, edata=0)

    at xc_ptrace.c:484

#2  0x0000000000405567 in linux_read_memory (memaddr=-2146406400, myaddr=0x7fffffbc22e0 "", len=Variable "len" is not available.

)

    at ../../../gdb-6.2.1/gdb/gdbserver/linux-xen-low.c:406

#3  0x000000000040437a in read_inferior_memory (memaddr=-2146406400, myaddr=0x7fffffbc22e0 "", len=1)

    at ../../../gdb-6.2.1/gdb/gdbserver/target.c:64

#4  0x0000000000403a4f in main (argc=4, argv=0x7fffffbc2bb8) at ../../../gdb-6.2.1/gdb/gdbserver/server.c:520

(gdb) f 0

#0  0x00002b7ee48a6b03 in map_domain_va (xc_handle=6, cpu=0, guest_va=0xffffffff80107000, perm=1) at xc_ptrace.c:384

384             page = page_array[va >> PAGE_SHIFT] << PAGE_SHIFT;

(gdb) list

379             unsigned long page;

380

381             if ( v != NULL )

382                 munmap(v, PAGE_SIZE);

383

384             page = page_array[va >> PAGE_SHIFT] << PAGE_SHIFT;

385

386             v = xc_map_foreign_range( xc_handle, current_domid, PAGE_SIZE,

387                     perm, page >> PAGE_SHIFT);

388

(gdb) p va

$1 = 18446744071563145216

(gdb) p/x va

$2 = 0xffffffff80107000

 

How are people debugging 32-bit domains from 64bit dom0?

---

From: Tan, Nicholas
Sent: Wednesday, July 05, 2006 10:41 AM
To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: GDB and exec mode on xen

 

One of the major problems I’m facing with connecting to a test kernel through xen is the fact that xen doesn’t seem to pass back an exec mode that gdb can use for different types of architectures (16/32/64bit). 

 

I’m wondering, what is the xen community doing in order to work around this issue?

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