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pdb documentation
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@@ -1,7 +1,7 @@
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Pervasive Debugging
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===================
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040205 Alex Ho (alex.ho at cl.cam.ac.uk)
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Alex Ho (alex.ho at cl.cam.ac.uk)
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Introduction
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------------
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@@ -79,12 +79,32 @@ Serial Port Configuration
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See: xeno.bk/tools/nsplitd
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nsplitd configuration
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---------------------
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hostname$ more /etc/xinetd.d/nsplit
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service nsplit1
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{
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socket_type = stream
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protocol = tcp
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wait = no
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user = wanda
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server = /usr/sbin/in.nsplitd
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server_args = serial.cl.cam.ac.uk:wcons00
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disable = no
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only_from = 128.232.0.0/17 127.0.0.1
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}
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hostname$ egrep 'wcons00|nsplit1' /etc/services
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wcons00 9600/tcp # Wanda remote console
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nsplit1 12010/tcp # Nemesis console splitter ports.
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Note: nsplitd was originally written for the Nemesis project
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at Cambridge.
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After nsplitd accepts a connection on <port>, it starts listening
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on port <port + 1>. Characters sent to the <port + 1> will have the
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high bit set and vice versa for characters received.
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After nsplitd accepts a connection on <port> (12010 in the above
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example), it starts listening on port <port + 1>. Characters sent
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to the <port + 1> will have the high bit set and vice versa for
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characters received.
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You can connect to the nsplitd using
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'tools/xenctl/lib/console_client.py <host> <port>'
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@@ -100,8 +120,9 @@ Usage
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1. Boot Xen and Linux
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2. Interrupt Xen by pressing 'D' at the console
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You should see the console message:
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pdb_handle_exception [0x88][0xfc5c9d88]
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At this point Xen is waiting for gdb commands on the serial line.
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(XEN) pdb_handle_exception [0x88][0x101000:0xfc5e72ac]
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At this point Xen is frozen and the pdb stub is waiting for gdb commands
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on the serial line.
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3. Attach with gdb
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(gdb) file xeno.bk/xen/xen
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Reading symbols from xeno.bk/xen/xen...done.
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@@ -146,60 +167,107 @@ Usage
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Program received signal SIGTRAP, Trace/breakpoint trap.
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release_task (p=0xc2da0000) at exit.c:51
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(gdb) print *p
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$3 = {state = 4, flags = 4, sigpending = 0, addr_limit = {seg = 3221225472},
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exec_domain = 0xc016a040, need_resched = 0, ptrace = 0, lock_depth = -1,
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counter = 1, nice = 0, policy = 0, mm = 0x0, processor = 0,
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cpus_runnable = 1, cpus_allowed = 4294967295, run_list = {next = 0x0,
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prev = 0x0}, sleep_time = 18995, next_task = 0xc017c000,
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prev_task = 0xc2f94000, active_mm = 0x0, local_pages = {next = 0xc2da0054,
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prev = 0xc2da0054}, allocation_order = 0, nr_local_pages = 0,
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binfmt = 0xc016c6a0, exit_code = 0, exit_signal = 17, pdeath_signal = 0,
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personality = 0, did_exec = -1, task_dumpable = 1, pid = 917, pgrp = 914,
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tty_old_pgrp = 0, session = 914, tgid = 917, leader = 0,
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p_opptr = 0xc2f94000, p_pptr = 0xc2f94000, p_cptr = 0x0, p_ysptr = 0x0,
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p_osptr = 0x0, thread_group = {next = 0xc2da00a8, prev = 0xc2da00a8},
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pidhash_next = 0x0, pidhash_pprev = 0xc01900b8, wait_chldexit = {
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lock = <incomplete type>, task_list = {next = 0xc2da00b8,
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prev = 0xc2da00b8}}, vfork_done = 0x0, rt_priority = 0,
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it_real_value = 0, it_prof_value = 0, it_virt_value = 0, it_real_incr = 0,
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it_prof_incr = 0, it_virt_incr = 0, real_timer = {list = {next = 0x0,
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prev = 0x0}, expires = 18950, data = 3269066752,
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function = 0xc000ce30 <it_real_fn>}, times = {tms_utime = 0,
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tms_stime = 0, tms_cutime = 0, tms_cstime = 0}, start_time = 18989,
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per_cpu_utime = {1}, per_cpu_stime = {310}, min_flt = 13, maj_flt = 104,
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nswap = 0, cmin_flt = 0, cmaj_flt = 0, cnswap = 0, swappable = -1, uid = 0,
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euid = 0, suid = 0, fsuid = 0, gid = 0, egid = 0, sgid = 0, fsgid = 0,
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ngroups = 7, groups = {0, 1, 2, 3, 4, 6, 10, 0 <repeats 25 times>},
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cap_effective = 4294967039, cap_inheritable = 0, cap_permitted = 4294967039,
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keep_capabilities = 0, user = 0xc016b18c, rlim = {{rlim_cur = 4294967295,
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rlim_max = 4294967295}, {rlim_cur = 4294967295, rlim_max = 4294967295}, {
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rlim_cur = 4294967295, rlim_max = 4294967295}, {rlim_cur = 8388608,
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rlim_max = 4294967295}, {rlim_cur = 0, rlim_max = 4294967295}, {
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rlim_cur = 4294967295, rlim_max = 4294967295}, {rlim_cur = 512,
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rlim_max = 512}, {rlim_cur = 1024, rlim_max = 1024}, {
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rlim_cur = 4294967295, rlim_max = 4294967295}, {rlim_cur = 4294967295,
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rlim_max = 4294967295}, {rlim_cur = 4294967295, rlim_max = 4294967295}},
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used_math = 0, comm = "id\000h\000og\000\000\000\000\000\000\000\000",
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link_count = 0, total_link_count = 1, tty = 0xc3ed1000, locks = 0,
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semundo = 0x0, semsleeping = 0x0, thread = {esp0 = 3269074944,
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eip = 3221249046, esp = 3269074792, fs = 0, gs = 0, io_pl = 3, debugreg = {
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0, 0, 0, 0, 0, 0, 0, 0}, cr2 = 0, trap_no = 0, error_code = 0, i387 = {
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fsave = {cwd = 2098047, swd = 125632512, twd = 1073944696, fip = 2091,
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fcs = -1073745032, foo = 2099, fos = 8064, st_space = {
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0 <repeats 20 times>}, status = 0}, fxsave = {cwd = 895, swd = 32,
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twd = 0, fop = 1917, fip = 1073944696, fcs = 2091, foo = -1073745032,
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fos = 2099, mxcsr = 8064, reserved = 0, st_space = {
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0 <repeats 24 times>, 1449431204, -1774489361, 16383, 0, 1,
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-1891252224, 16404, 0}, xmm_space = {0 <repeats 32 times>},
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padding = {0 <repeats 56 times>}}, soft = {cwd = 2098047,
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swd = 125632512, twd = 1073944696, fip = 2091, fcs = -1073745032,
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foo = 2099, fos = 8064, st_space = {0 <repeats 20 times>},
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ftop = 0 '\0', changed = 0 '\0', lookahead = 0 '\0',
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no_update = 0 '\0', rm = 0 '\0', alimit = 0 '\0', info = 0x0,
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entry_eip = 0}}, vm86_info = 0x0, screen_bitmap = 0, v86flags = 0,
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v86mask = 0, saved_esp0 = 0}, fs = 0x0, files = 0x0, namespace = 0x0,
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sigmask_lock = <incomplete type>, sig = 0x0, blocked = {sig = {0, 0}},
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pending = {head = 0x0, tail = 0xc2da04f8, signal = {sig = {0, 0}}},
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sas_ss_sp = 0, sas_ss_size = 0, notifier = 0, notifier_data = 0x0,
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notifier_mask = 0x0, parent_exec_id = 7, self_exec_id = 8,
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alloc_lock = <incomplete type>, journal_info = 0x0}
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$3 = {state = 4, flags = 4, sigpending = 0, addr_limit = {seg = 3221225472},
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exec_domain = 0xc016a040, need_resched = 0, ptrace = 0, lock_depth = -1,
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counter = 1, nice = 0, policy = 0, mm = 0x0, processor = 0,
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cpus_runnable = 1, cpus_allowed = 4294967295, run_list = {next = 0x0,
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prev = 0x0}, sleep_time = 18995, next_task = 0xc017c000,
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prev_task = 0xc2f94000, active_mm = 0x0, local_pages = {next = 0xc2da0054,
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prev = 0xc2da0054}, allocation_order = 0, nr_local_pages = 0,
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...
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5. To resume Xen, enter the "continue" command to gdb.
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This sends the packet $c#63 along the serial channel.
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(gdb) cont
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Continuing.
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Debugging Multiple Domains & Processes
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--------------------------------------
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pdb supports debugging multiple domains & processes. You can switch
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between different domains and processes within domains and examine
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variables in each.
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The pdb context identifies the current debug target. It is stored
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in the xen variable pdb_ctx and defaults to xen.
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target pdb_ctx.domain pdb_ctx.process
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------ -------------- ---------------
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xen -1 -1
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guest os 0,1,2,... -1
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process 0,1,2,... 0,1,2,...
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Unfortunately, gdb doesn't understand debugging multiple process
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simultaneously (we're working on it), so at present you are limited
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to just one set of symbols for symbolic debugging. When debugging
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processes, pdb currently supports just Linux 2.4.
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define setup
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file xeno-clone/xeno.bk/xen/xen
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add-sym xeno-clone/xenolinux-2.4.25/vmlinux
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add-sym ~ach61/a.out
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end
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1. Connect with gdb as before. A couple of Linux-specific
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symbols need to be defined.
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(gdb) target remote <hostname>:<port + 1> /* contact nsplitd */
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Remote debugging using serial.srg:12131
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continue_cpu_idle_loop () at current.h:10
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warning: shared library handler failed to enable breakpoint
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(gdb) set pdb_pidhash_addr = &pidhash
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(gdb) set pdb_init_task_union_addr = &init_task_union
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2. The pdb context defaults to Xen and we can read Xen's memory.
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An attempt to access domain 0 memory fails.
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(gdb) print pdb_ctx
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$1 = {valid = 0, domain = -1, process = -1, ptbr = 1052672}
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(gdb) print hexchars
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$2 = "0123456789abcdef"
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(gdb) print cpu_vendor_names
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Cannot access memory at address 0xc0191f80
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3. Now we change to domain 0. In addition to changing pdb_ctx.domain,
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we need to change pdb_ctx.valid to signal pdb of the change.
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It is now possible to examine Xen and Linux memory.
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(gdb) set pdb_ctx.domain=0
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(gdb) set pdb_ctx.valid=1
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(gdb) print hexchars
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$3 = "0123456789abcdef"
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(gdb) print cpu_vendor_names
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$4 = {0xc0158b46 "Intel", 0xc0158c37 "Cyrix", 0xc0158b55 "AMD",
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0xc0158c3d "UMC", 0xc0158c41 "NexGen", 0xc0158c48 "Centaur",
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0xc0158c50 "Rise", 0xc0158c55 "Transmeta"}
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4. Now change to a process within domain 0. Again, we need to
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change pdb_ctx.valid in addition to pdb_ctx.process.
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(gdb) set pdb_ctx.process=962
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(gdb) set pdb_ctx.valid =1
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(gdb) print pdb_ctx
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$1 = {valid = 0, domain = 0, process = 962, ptbr = 52998144}
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(gdb) print aho_a
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$2 = 20
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5. Now we can read the same variable from another process running
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the same executable in another domain.
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(gdb) set pdb_ctx.domain=1
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(gdb) set pdb_ctx.process=1210
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(gdb) set pdb_ctx.valid=1
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(gdb) print pdb_ctx
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$3 = {valid = 0, domain = 1, process = 1210, ptbr = 70574080}
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(gdb) print aho_a
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$4 = 27
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Changes
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-------
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04.02.05 aho creation
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04.03.31 aho add description on debugging multiple domains
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@@ -7,7 +7,7 @@
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* 2004
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* university of cambridge computer laboratory
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*
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* code adapted originally from kgdb & nemesis
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* code adapted originally from kgdb, nemesis, & gdbserver
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*/
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#include <xen/lib.h>
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@@ -21,8 +21,8 @@
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#include <xen/list.h>
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#include <xen/serial.h>
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#undef DEBUG_TRACE
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#ifdef DEBUG_TRACE
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#undef PDB_DEBUG_TRACE
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#ifdef PDB_DEBUG_TRACE
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#define TRC(_x) _x
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#else
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#define TRC(_x)
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