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commit 6eeee81c8e59511962bdd83df5e7785bfdf871d2
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Author: Tom Tromey <tromey@redhat.com>
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Date: Fri Nov 22 17:38:44 2013 +0000
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Detect infinite loop in value_fetch_lazy's lval_register handling.
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If value_fetch_lazy loops infinitely while unwrapping lval_register
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values, it means we either somehow ended up with two frames with the
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same ID in the frame chain, or some code is trying to unwind behind
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get_prev_frame's back (e.g., a frame unwind sniffer trying to unwind).
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In any case, it should always be an internal error to end up in this
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situation.
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This patch adds a check and throws an internal error if the same frame
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is returned.
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2013-11-22 Tom Tromey <tromey@redhat.com>
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Pedro Alves <palves@redhat.com>
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PR backtrace/16155
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* value.c (value_fetch_lazy): Internal error if
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get_frame_register_value returns the same register.
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Index: gdb-7.6.1/gdb/valops.c
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===================================================================
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--- gdb-7.6.1.orig/gdb/valops.c
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+++ gdb-7.6.1/gdb/valops.c
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@@ -1093,7 +1093,9 @@ value_fetch_lazy (struct value *val)
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while (VALUE_LVAL (new_val) == lval_register && value_lazy (new_val))
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{
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- frame = frame_find_by_id (VALUE_FRAME_ID (new_val));
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+ struct frame_id frame_id = VALUE_FRAME_ID (new_val);
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+
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+ frame = frame_find_by_id (frame_id);
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regnum = VALUE_REGNUM (new_val);
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gdb_assert (frame != NULL);
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@@ -1107,6 +1109,22 @@ value_fetch_lazy (struct value *val)
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regnum, type));
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new_val = get_frame_register_value (frame, regnum);
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+
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+ /* If we get another lazy lval_register value, it means the
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+ register is found by reading it from the next frame.
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+ get_frame_register_value should never return a value with
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+ the frame id pointing to FRAME. If it does, it means we
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+ either have two consecutive frames with the same frame id
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+ in the frame chain, or some code is trying to unwind
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+ behind get_prev_frame's back (e.g., a frame unwind
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+ sniffer trying to unwind), bypassing its validations. In
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+ any case, it should always be an internal error to end up
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+ in this situation. */
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+ if (VALUE_LVAL (new_val) == lval_register
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+ && value_lazy (new_val)
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+ && frame_id_eq (VALUE_FRAME_ID (new_val), frame_id))
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+ internal_error (__FILE__, __LINE__,
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+ _("infinite loop while fetching a register"));
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}
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/* If it's still lazy (for instance, a saved register on the
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