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Re: prev_pc problem on ia64
- From: Elena Zannoni <ezannoni at redhat dot com>
- To: "J. Johnston" <jjohnstn at redhat dot com>
- Cc: gdb at sources dot redhat dot com
- Date: Mon, 14 Apr 2003 16:21:39 -0400
- Subject: Re: prev_pc problem on ia64
- References: <3E973FEB.1090500@redhat.com>
J. Johnston writes:
> I am running into a problem on ia64 regarding performing a next
> after an inferior function call or after using "return" from
> a function.
>
> What's occurring is that an inferior function call ends up setting
> the static prev_pc value in infrun.c: stop_stepping(). When we
> return to the gdb prompt prev_pc is not restored to its original
> value. A similar problem occurs when we return from a function
> using the gdb return command.
>
Can you post the sequence that will make the error occur? stop_stepping
is not called by the inferior function call code. So it must be
afterwards.
> On the ia64, there are extraneous line table entries that do not
> increase the line number. When we perform a next after the inferior
> call, we step until the line number changes from the one set for
> prev_pc. Unfortunately, this only gets us part way through the line as
> we run until the next line table entry.
>
> For the x86, this problem does not crop up in the test case I am looking
> at because there are none of these additional line table entries. When
> we perform a next, it finds the next line regardless of the fact that prev_pc is
> not correctly set.
>
> The following is an example of the line table entries I am talking about on
> the ia64 (generated by readelf -wl). I am using a recent gcc but this behavior
> also occurs for gcc 2.96
>
> Special opcode 20: advance Address by 1 to 0x40000000000007e1 and Line by 1 to 31
> Special opcode 215: advance Address by 15 to 0x40000000000007f0 and Line by 0 to 31
> Special opcode 19: advance Address by 1 to 0x40000000000007f1 and Line by 0 to 31
> Special opcode 19: advance Address by 1 to 0x40000000000007f2 and Line by 0 to 31
> Special opcode 201: advance Address by 14 to 0x4000000000000800 and Line by 0 to 31
> Special opcode 20: advance Address by 1 to 0x4000000000000801 and Line by 1 to 32
> Special opcode 243: advance Address by 17 to 0x4000000000000812 and Line by 0 to 32
> Special opcode 201: advance Address by 14 to 0x4000000000000820 and Line by 0 to 32
> Special opcode 19: advance Address by 1 to 0x4000000000000821 and Line by 0 to 32
> Special opcode 19: advance Address by 1 to 0x4000000000000822 and Line by 0 to 32
> Special opcode 201: advance Address by 14 to 0x4000000000000830 and Line by 0 to 32
> Special opcode 19: advance Address by 1 to 0x4000000000000831 and Line by 0 to 32
>
What does gdb show for info line 31 and info line 32? How about
disasembling instructions around those lines? I wonder if these
addresses are legitimate at all.
> Same function compiled for i686:
>
> Special opcode 76: advance Address by 5 to 0x804839e and Line by 1 to 31
> Special opcode 230: advance Address by 16 to 0x80483ae and Line by 1 to 32
> Special opcode 146: advance Address by 10 to 0x80483b8 and Line by 1 to 33
> Special opcode 160: advance Address by 11 to 0x80483c3 and Line by 1 to 34
>
> I have a patch whereby I reset prev_pc in infrun.c:init_execution_control_state():
>
> if (prev_pc != 0)
> prev_pc = read_pc ();
>
> prior to setting the ecs->sal. This works for me in both scenarios. The check for
> 0 was needed because I get a failure on the ia64 trying to read the pc too early when
> the psr register was invalid.
>
maybe read_pc should return an error code? Ah wait, it errors out, so
you should encapsulate that in a catch_errors().
please post the patch to gdb-patches. It's hard to judge, like this.
> This may or may not be the best way of doing this. Any other platforms experiencing
> this problem in call-ar-st.exp or return.exp?
>
Not that I remember.
elena
> -- Jeff J.