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qemu-gdb: allow using glibc_pointer_guard() on core dumps

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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>
This commit is contained in:
Paolo Bonzini 2015-10-12 10:02:52 +02:00 committed by Stefan Hajnoczi
parent 7bc8e0c967
commit 1138f24645
1 changed files with 16 additions and 2 deletions
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18
scripts/qemugdb/coroutine.py
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@ -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, $rsp - 120)', False, True)
@ -24,9 +25,22 @@ def get_fs_base():
gdb.execute('set *(uint64_t*)($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):