From 1138f24645e9e1e2d55d280caab4e2539dfcdb49 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Mon, 12 Oct 2015 10:02:52 +0200 Subject: [PATCH] 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 Message-id: 1444636974-19950-2-git-send-email-pbonzini@redhat.com Signed-off-by: Stefan Hajnoczi --- scripts/qemugdb/coroutine.py | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/scripts/qemugdb/coroutine.py b/scripts/qemugdb/coroutine.py index 3c54918b5d..b1d4546fe6 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, $rsp - 120)', False, True) @@ -24,9 +25,22 @@ def get_fs_base(): gdb.execute('set *(uint64_t*)($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):