qemu-gdb: allow using glibc_pointer_guard() on core dumps
get_fs_base() cannot be run on a core dump, because it uses the arch_prctl
system call. The fs base is the value that is returned by pthread_self(),
and it would be nice to just glean it from the "info threads" output:
* 1 Thread 0x7f16a3fff700 (LWP 33642) pthread_cond_wait@@GLIBC_2.3.2 ()
^^^^^^^^^^^^^^
but unfortunately the gdb API does not provide that. Instead, we can
look for the "arg" argument of the start_thread function if glibc debug
information are available. If not, fall back to the old mechanism.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1444636974-19950-2-git-send-email-pbonzini@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/scripts/qemugdb/coroutine.py b/scripts/qemugdb/coroutine.py
index 3c54918..b1d4546 100644
--- a/scripts/qemugdb/coroutine.py
+++ b/scripts/qemugdb/coroutine.py
@@ -16,7 +16,8 @@
import gdb
def get_fs_base():
- '''Fetch %fs base value using arch_prctl(ARCH_GET_FS)'''
+ '''Fetch %fs base value using arch_prctl(ARCH_GET_FS). This is
+ pthread_self().'''
# %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, $rsp - 120)', False, True)
@@ -24,9 +25,22 @@
gdb.execute('set *(uint64_t*)($rsp - 120) = %s' % old, False, True)
return fs_base
+def pthread_self():
+ '''Fetch pthread_self() from the glibc start_thread function.'''
+ f = gdb.newest_frame()
+ while f.name() != 'start_thread':
+ f = f.older()
+ if f is None:
+ return get_fs_base()
+
+ try:
+ return f.read_var("arg")
+ except ValueError:
+ return get_fs_base()
+
def get_glibc_pointer_guard():
'''Fetch glibc pointer guard value'''
- fs_base = get_fs_base()
+ fs_base = pthread_self()
return gdb.parse_and_eval('*(uint64_t*)((uint64_t)%s + 0x30)' % fs_base)
def glibc_ptr_demangle(val, pointer_guard):
