When debugging a coredump, pthread_self can't be obtained from
function arch_prctl. Moreover if qemu crashed in coroutine, we
can't find 'start_thread' in current stack-trace. So, add a method,
actually proposed in 1138f24645e9e, which should work for gdb
version >= 7.3.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 scripts/qemugdb/coroutine.py | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/scripts/qemugdb/coroutine.py b/scripts/qemugdb/coroutine.py
index ab699794ab..ffaa45c464 100644
--- a/scripts/qemugdb/coroutine.py
+++ b/scripts/qemugdb/coroutine.py
@@ -14,6 +14,7 @@
 # GNU GPL, version 2 or (at your option) any later version.
 
 import gdb
+import re
 
 VOID_PTR = gdb.lookup_type('void').pointer()
 
@@ -28,7 +29,17 @@ def get_fs_base():
     return fs_base
 
 def pthread_self():
-    '''Fetch pthread_self() from the glibc start_thread function.'''
+    # Try read pthread_self from gdb command 'info threads'.
+    # Will fail for old gdb.
+    try:
+        threads = gdb.execute('info threads', False, True)
+        m = re.search('^\* 1    Thread (0x[0-9a-f]+)', threads, re.MULTILINE)
+        return int(m.group(1), 16)
+    except TypeError:
+        # gdb doesn't support third parameter for execute
+        pass
+
+    # Try fetch pthread_self() from the glibc start_thread function.
     f = gdb.newest_frame()
     while f.name() != 'start_thread':
         f = f.older()
-- 
2.11.1

On 28/03/2018 19:32, Vladimir Sementsov-Ogievskiy wrote:
> When debugging a coredump, pthread_self can't be obtained from
> function arch_prctl. Moreover if qemu crashed in coroutine, we
> can't find 'start_thread' in current stack-trace. So, add a method,
> actually proposed in 1138f24645e9e, which should work for gdb
> version >= 7.3.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

New-enough gdb can also use gdb.selected_thread()
> ---
>  scripts/qemugdb/coroutine.py | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/scripts/qemugdb/coroutine.py b/scripts/qemugdb/coroutine.py
> index ab699794ab..ffaa45c464 100644
> --- a/scripts/qemugdb/coroutine.py
> +++ b/scripts/qemugdb/coroutine.py
> @@ -14,6 +14,7 @@
>  # GNU GPL, version 2 or (at your option) any later version.
>  
>  import gdb
> +import re
>  
>  VOID_PTR = gdb.lookup_type('void').pointer()
>  
> @@ -28,7 +29,17 @@ def get_fs_base():
>      return fs_base
>  
>  def pthread_self():
> -    '''Fetch pthread_self() from the glibc start_thread function.'''
> +    # Try read pthread_self from gdb command 'info threads'.
> +    # Will fail for old gdb.
> +    try:
> +        threads = gdb.execute('info threads', False, True)
> +        m = re.search('^\* 1    Thread (0x[0-9a-f]+)', threads, re.MULTILINE)

I don't think hard-coding "1" works here, and the spacing of the table
might differ as well.  However, looking for the asterisk seems safe from
a quick look at gdb source, and "Thread" looks like it isn't localized.

Paolo

> +        return int(m.group(1), 16)
> +    except TypeError:
> +        # gdb doesn't support third parameter for execute
> +        pass
> +
> +    # Try fetch pthread_self() from the glibc start_thread function.
>      f = gdb.newest_frame()
>      while f.name() != 'start_thread':
>          f = f.older()
> 

On Wed, Mar 28, 2018 at 08:32:35PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> When debugging a coredump, pthread_self can't be obtained from
> function arch_prctl. Moreover if qemu crashed in coroutine, we
> can't find 'start_thread' in current stack-trace. So, add a method,
> actually proposed in 1138f24645e9e, which should work for gdb
> version >= 7.3.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  scripts/qemugdb/coroutine.py | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>