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fix frame_unwind_id assertion
- From: Pedro Alves <pedro at codesourcery dot com>
- To: gdb-patches at sourceware dot org
- Date: Tue, 20 May 2008 23:12:03 +0100
- Subject: fix frame_unwind_id assertion
This patch fixes the gdb_assert hit I found here:
http://sourceware.org/ml/gdb-patches/2008-05/msg00516.html
The assert being hit happens here, when calling
frame_unwind_id (get_current_frame ()) right after
deciding we have an event to handle in handle_inferior_event:
static void
frame_cleanup_after_sniffer (void *arg)
{
...
/* No sniffer should extend the frame chain; sniff based on what is
already certain. */
gdb_assert (!frame->prev_p);
#0 internal_error (file=0x7558a1 "../../src/gdb/frame.c", line=1808,
string=0x755946 "%s: Assertion `%s' failed.")
at ../../src/gdb/utils.c:779
#1 0x00000000005b5b6a in frame_cleanup_after_sniffer (arg=0xafbd40)
at ../../src/gdb/frame.c:1808
#2 0x00000000004570ed in do_my_cleanups (pmy_chain=0xa9b900,
old_chain=0xb13d10) at ../../src/gdb/utils.c:320
#3 0x000000000045709d in do_cleanups (old_chain=0xb13d10)
at ../../src/gdb/utils.c:303
#4 0x00000000005b62d3 in frame_unwind_find_by_frame (this_frame=0xafbd40,
this_cache=0xafbd48)
at ../../src/gdb/frame-unwind.c:105
#5 0x00000000005b2e7f in get_frame_id (fi=0xafbd40)
at ../../src/gdb/frame.c:258
#6 0x00000000005b4c6a in get_prev_frame_1 (this_frame=0xafbd40)
at ../../src/gdb/frame.c:1188
#7 0x00000000005b2f72 in frame_unwind_id (next_frame=0xafbd40)
at ../../src/gdb/frame.c:279
#8 0x0000000000503b00 in handle_inferior_event (ecs=0x7fffd6bca510)
at ../../src/gdb/infrun.c:2605
#9 0x00000000005016cb in wait_for_inferior (treat_exec_as_sigtrap=0)
at ../../src/gdb/infrun.c:1482
#10 0x000000000050142d in proceed (addr=18446744073709551615,
siggnal=TARGET_SIGNAL_DEFAULT, step=1)
at ../../src/gdb/infrun.c:1273
#11 0x00000000004fd64f in step_1 (skip_subroutines=1, single_inst=0,
count_string=0x0) at ../../src/gdb/infcmd.c:784
#12 0x00000000004fd32e in next_command (count_string=0x0, from_tty=1)
at ../../src/gdb/infcmd.c:678
...
The problem triggers whenever the first thing we do with a
frame is to call something that calls get_prev_frame_1, before
the frame having an unwinder and a frame id set.
We weren't seeing this happen, because normally we're calling
get_frame_id before frame_unwind_id:
/* Check for subroutine calls. The check for the current frame
equalling the step ID is not necessary - the check of the
previous frame's ID is sufficient - but it is a common case and
cheaper than checking the previous frame's ID.
NOTE: frame_id_eq will never report two invalid frame IDs as
being equal, so to get into this block, both the current and
previous frame must have valid frame IDs. */
if (!frame_id_eq (get_frame_id (get_current_frame ()), step_frame_id)
&& frame_id_eq (frame_unwind_id (get_current_frame ()), step_frame_id))
{
CORE_ADDR real_stop_pc;
It happened that my new call to frame_unwind_id was earlier than that bit.
Since get_frame_id only does the work once,
struct frame_id
get_frame_id (struct frame_info *fi)
{
if (fi == NULL)
{
return null_frame_id;
}
if (!fi->this_id.p)
{
...
fi->this_id.p = 1;
}
return fi->this_id.value;
}
... this sequence was safe:
static struct frame_info *
get_prev_frame_1 (struct frame_info *this_frame)
{
this_frame->prev_p = 1;
this_frame->stop_reason = UNWIND_NO_REASON;
/* Check that this frame's ID was valid. If it wasn't, don't try to
unwind to the prev frame. Be careful to not apply this test to
the sentinel frame. */
this_id = get_frame_id (this_frame); <<<< hits already built id.
Tested on x86_64-unknown-linux-gnu, no regressions.
OK?
--
Pedro Alves
2008-05-20 Pedro Alves <pedro@codesourcery.com>
* frame.c (get_prev_frame_1): Build frame id before setting
this_frame->prev_p, not after.
---
gdb/frame.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
Index: src/gdb/frame.c
===================================================================
--- src.orig/gdb/frame.c 2008-05-20 22:41:07.000000000 +0100
+++ src/gdb/frame.c 2008-05-20 22:49:59.000000000 +0100
@@ -1179,13 +1179,17 @@ get_prev_frame_1 (struct frame_info *thi
}
return this_frame->prev;
}
+
+ /* If the frame id hasn't been built yet, it must be done before
+ setting a stop reason. */
+ this_id = get_frame_id (this_frame);
+
this_frame->prev_p = 1;
this_frame->stop_reason = UNWIND_NO_REASON;
/* Check that this frame's ID was valid. If it wasn't, don't try to
unwind to the prev frame. Be careful to not apply this test to
the sentinel frame. */
- this_id = get_frame_id (this_frame);
if (this_frame->level >= 0 && !frame_id_p (this_id))
{
if (frame_debug)