From: Stefan Hajnoczi <stefa...@redhat.com>
The 'qemu coroutine <coroutine-address>' GDB command prints the
backtrace for a CoroutineUContext. This is useful for peeking inside
yielded coroutines that are waiting for file descriptor events, timers,
etc.
For example:
$ gdb tests/test-coroutine
(gdb) b test_yield
(gdb) r
(gdb) b qemu_coroutine_enter
(gdb) c
(gdb) c
Continuing.
Breakpoint 2, qemu_coroutine_enter (co=0x555555c66520, opaque=0x0) at
qemu-coroutine.c:103
103 {
(gdb) source scripts/qemu-gdb.py
(gdb) qemu coroutine 0x555555c66520
#0 0x000055555557a740 in qemu_coroutine_switch (from_=<optimized out>,
to_=0x7ffff7f90a70, action=COROUTINE_YIELD) at coroutine-ucontext.c:177
#1 0x0000555555566af9 in yield_5_times (opaque=0x7fffffffdbb7) at
tests/test-coroutine.c:107
#2 0x000055555557a7aa in coroutine_trampoline (i0=<optimized out>,
i1=<optimized out>) at coroutine-ucontext.c:80
#3 0x00007ffff08de000 in __start_context () at /lib64/libc.so.6
Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
Message-id: 1427409754-8556-1-git-send-email-stefa...@redhat.com
Signed-off-by: Kevin Wolf <kw...@redhat.com>
---
scripts/qemu-gdb.py | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 75 insertions(+)
diff --git a/scripts/qemu-gdb.py b/scripts/qemu-gdb.py
index 8a0f305..6c7f4fb 100644
--- a/scripts/qemu-gdb.py
+++ b/scripts/qemu-gdb.py
@@ -22,12 +22,86 @@ def isnull(ptr):
def int128(p):
return long(p['lo']) + (long(p['hi']) << 64)
+def get_fs_base():
+ '''Fetch %fs base value using arch_prctl(ARCH_GET_FS)'''
+ # %rsp - 120 is scratch space according to the SystemV ABI
+ old = gdb.parse_and_eval('*(uint64_t*)($rsp - 120)')
+ gdb.execute('call arch_prctl(0x1003, $rsp - 120)', False, True)
+ fs_base = gdb.parse_and_eval('*(uint64_t*)($rsp - 120)')
+ gdb.execute('set *(uint64_t*)($rsp - 120) = %s' % old, False, True)
+ return fs_base
+
+def get_glibc_pointer_guard():
+ '''Fetch glibc pointer guard value'''
+ fs_base = get_fs_base()
+ return gdb.parse_and_eval('*(uint64_t*)((uint64_t)%s + 0x30)' % fs_base)
+
+def glibc_ptr_demangle(val, pointer_guard):
+ '''Undo effect of glibc's PTR_MANGLE()'''
+ return gdb.parse_and_eval('(((uint64_t)%s >> 0x11) | ((uint64_t)%s << (64
- 0x11))) ^ (uint64_t)%s' % (val, val, pointer_guard))
+
+def bt_jmpbuf(jmpbuf):
+ '''Backtrace a jmpbuf'''
+ JB_RBX = 0
+ JB_RBP = 1
+ JB_R12 = 2
+ JB_R13 = 3
+ JB_R14 = 4
+ JB_R15 = 5
+ JB_RSP = 6
+ JB_PC = 7
+
+ old_rbx = gdb.parse_and_eval('(uint64_t)$rbx')
+ old_rbp = gdb.parse_and_eval('(uint64_t)$rbp')
+ old_rsp = gdb.parse_and_eval('(uint64_t)$rsp')
+ old_r12 = gdb.parse_and_eval('(uint64_t)$r12')
+ old_r13 = gdb.parse_and_eval('(uint64_t)$r13')
+ old_r14 = gdb.parse_and_eval('(uint64_t)$r14')
+ old_r15 = gdb.parse_and_eval('(uint64_t)$r15')
+ old_rip = gdb.parse_and_eval('(uint64_t)$rip')
+
+ pointer_guard = get_glibc_pointer_guard()
+ gdb.execute('set $rbx = %s' % jmpbuf[JB_RBX])
+ gdb.execute('set $rbp = %s' % glibc_ptr_demangle(jmpbuf[JB_RBP],
pointer_guard))
+ gdb.execute('set $rsp = %s' % glibc_ptr_demangle(jmpbuf[JB_RSP],
pointer_guard))
+ gdb.execute('set $r12 = %s' % jmpbuf[JB_R12])
+ gdb.execute('set $r13 = %s' % jmpbuf[JB_R13])
+ gdb.execute('set $r14 = %s' % jmpbuf[JB_R14])
+ gdb.execute('set $r15 = %s' % jmpbuf[JB_R15])
+ gdb.execute('set $rip = %s' % glibc_ptr_demangle(jmpbuf[JB_PC],
pointer_guard))
+
+ gdb.execute('bt')
+
+ gdb.execute('set $rbx = %s' % old_rbx)
+ gdb.execute('set $rbp = %s' % old_rbp)
+ gdb.execute('set $rsp = %s' % old_rsp)
+ gdb.execute('set $r12 = %s' % old_r12)
+ gdb.execute('set $r13 = %s' % old_r13)
+ gdb.execute('set $r14 = %s' % old_r14)
+ gdb.execute('set $r15 = %s' % old_r15)
+ gdb.execute('set $rip = %s' % old_rip)
+
class QemuCommand(gdb.Command):
'''Prefix for QEMU debug support commands'''
def __init__(self):
gdb.Command.__init__(self, 'qemu', gdb.COMMAND_DATA,
gdb.COMPLETE_NONE, True)
+class CoroutineCommand(gdb.Command):
+ '''Display coroutine backtrace'''
+ def __init__(self):
+ gdb.Command.__init__(self, 'qemu coroutine', gdb.COMMAND_DATA,
+ gdb.COMPLETE_NONE)
+
+ def invoke(self, arg, from_tty):
+ argv = gdb.string_to_argv(arg)
+ if len(argv) != 1:
+ gdb.write('usage: qemu coroutine <coroutine-pointer>\n')
+ return
+
+ coroutine_pointer =
gdb.parse_and_eval(argv[0]).cast(gdb.lookup_type('CoroutineUContext').pointer())
+ bt_jmpbuf(coroutine_pointer['env']['__jmpbuf'])
+
class MtreeCommand(gdb.Command):
'''Display the memory tree hierarchy'''
def __init__(self):
@@ -86,4 +160,5 @@ class MtreeCommand(gdb.Command):
subregion = subregion['subregions_link']['tqe_next']
QemuCommand()
+CoroutineCommand()
MtreeCommand()
--
1.8.3.1
