[Gdb] Re: stepping problem with sh4, gdbserver

[peter garrone]

I made some errors due to fact the copy of gdb was optimised. apologies. 
The break PC for the prior run of handle_inferior_event was assumed to be the 
current runs value.

> 
> Hi,
>   While debugging remotely with gdbserver and stepping the gdb 
> (6.3) test program "break.c" at line 96, the "next" command causes 
> a segfault at frame.c line 1244 (frame->next != NULL) because frame 
> is null. The relevant backtrace is:
> 
> get_frame_pc(frame = 0)  frame.c:1244
> insert_step_resume_breakpoint_at_frame(return_frame=0) infrun.c:2670
> handle_inferior_event infrun.c:2449
> wait_for_inferior infrun.c:991
> 
> Tracing the execution of gdb itself, handle_inferior_event is 
> invoked 
when the target hits a break at the subroutine, whereopon gdb sets a break at 
the subroutine return point.
When it hits this return point break, it appears to erroneously pass the 
frame_id_eq test at infrun.c:2285
The data passed to frame_id_eq is identical to the previous invocation when gdb 
was servicing the break within the subroutine.
According to the block comment, it is only entered when a subroutine is 
debugged, so I assume this is an error.

So gdb appears to be mistakenly assuming that it is in a subroutine when in 
fact it has returned.

 
> I am using gdb 6.3, but have seen a similar error on previous 
> versions. Configuration is for sh4-xxx-linux-gnu, gdb_target=linux, 
> --enable-shared, --enable-threads
> The only relevant source change is an include in 
> gdbserver/linux-sh-low.c where #include <sys/reg.h> is commented 
> out.
> 
> Any help appreciated.
> Peter Garrone
> --

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