[RFA] enable software single step on alpha-osf
Joel Brobecker
brobecker@gnat.com
Thu Jul 18 13:55:00 GMT 2002
One of our customers who is using multi-processor alpha-osf machines
has informed us that the next/step operations do not function correctly
on their machine.
Among other things, they saw messages like these:
Program received signal SIGSEGV, Segmentation fault
<__gnat_malloc> (size=8208) at s-memory.adb:92
or
Program received signal SIGTRAP, Trace/breakpoint trap.
0x1201ee89c in mate.types.data....
or sometimes the behavior of the program becomes odd, and the
debugger stops at a bizarre location...
It turned out that procfs does not seem to be handling multi-cpu machines
very well, as far as next/step operations are concerned. We could not
test this ourselves, because we don't have a multi-cpu alpha-osf
machine, but as soon as we enabled the software-single-step capability,
most these problems were gone...
Other problems surfaced, however. The SIGSEGVs and the SIGTRAPs
disappeared, but "next" sometimes stopped at the wrong location.
The following patch enables software single stepping. It also fixes
all the problems I found when comparing the testsuite results before and
after the switch. The test results are now identical before and after my
changes. For the record, here is a summary of the results I get:
# of expected passes 7246
# of unexpected failures 680
# of unexpected successes 5
# of expected failures 149
# of unresolved testcases 59
# of untested testcases 3
# of unsupported tests 2
I also verified on a linux machine, where software
single-stepping is not enabled, that no regression was introduced.
It would be interesting to see how this change influences the results
of alpha-netbsd. It should improve them.
Ok to commit?
2002-07-18 Joel Brobecker <brobecker@gnat.com>
* alpha-osf1-tdep.c (alpha_osf1_init_abi): Unfortunately,
procfs appears to be broken when debugging on multi-processor
machines. So enable software single stepping in order to avoid
using the procfs interface to do next/step operations, using
internal breakpoints instead.
* infrun.c (handle_inferior_event): When receiving a SIGTRAP
signal, check whether we hit a breakpoint before checking for a
single step breakpoint. Otherwise, GDB fails to notice that a
breakpoint has been hit when stepping onto a breakpoint.
Readjust the stop_pc by DECR_PC_AFTER_BREAK when hitting a
single step breakpoint, to make this pc address equal to the
value it would have if the system stepping capability was used.
* breakpoint.c (bpstat_stop_status): Do not adjust the PC
address by DECR_PC_AFTER_BREAK when software single step is
in use for this architecture, as this has already been taken
care of in handle_inferior_event().
--
Joel
-------------- next part --------------
Index: alpha-osf1-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/alpha-osf1-tdep.c,v
retrieving revision 1.5
diff -c -3 -p -r1.5 alpha-osf1-tdep.c
*** alpha-osf1-tdep.c 21 May 2002 15:36:02 -0000 1.5
--- alpha-osf1-tdep.c 18 Jul 2002 20:29:34 -0000
*************** alpha_osf1_init_abi (struct gdbarch_info
*** 58,63 ****
--- 58,67 ----
struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
set_gdbarch_pc_in_sigtramp (gdbarch, alpha_osf1_pc_in_sigtramp);
+ /* The next/step support via procfs on OSF1 is broken when running
+ on multi-processor machines. We need to use software single stepping
+ instead. */
+ set_gdbarch_software_single_step (gdbarch, alpha_software_single_step);
tdep->skip_sigtramp_frame = alpha_osf1_skip_sigtramp_frame;
tdep->sigcontext_addr = alpha_osf1_sigcontext_addr;
Index: infrun.c
===================================================================
RCS file: /cvs/src/src/gdb/infrun.c,v
retrieving revision 1.63
diff -c -3 -p -r1.63 infrun.c
*** infrun.c 18 Jul 2002 17:53:49 -0000 1.63
--- infrun.c 18 Jul 2002 20:29:36 -0000
*************** handle_inferior_event (struct execution_
*** 1826,1835 ****
if (stop_signal == TARGET_SIGNAL_TRAP)
{
! if (SOFTWARE_SINGLE_STEP_P () && singlestep_breakpoints_inserted_p)
! ecs->random_signal = 0;
! else if (breakpoints_inserted
! && breakpoint_here_p (stop_pc - DECR_PC_AFTER_BREAK))
{
ecs->random_signal = 0;
if (!breakpoint_thread_match (stop_pc - DECR_PC_AFTER_BREAK,
--- 1826,1836 ----
if (stop_signal == TARGET_SIGNAL_TRAP)
{
! /* Check if a regular breakpoint has been hit before checking
! for a potential single step breakpoint. Otherwise, GDB will
! not see this breakpoint hit when stepping onto breakpoints. */
! if (breakpoints_inserted
! && breakpoint_here_p (stop_pc - DECR_PC_AFTER_BREAK))
{
ecs->random_signal = 0;
if (!breakpoint_thread_match (stop_pc - DECR_PC_AFTER_BREAK,
*************** handle_inferior_event (struct execution_
*** 1885,1890 ****
--- 1886,1901 ----
}
}
}
+ else if (SOFTWARE_SINGLE_STEP_P () && singlestep_breakpoints_inserted_p)
+ {
+ /* Readjust the stop_pc as it is off by DECR_PC_AFTER_BREAK
+ compared to the value it would have if the system stepping
+ capability was used. This allows the rest of the code in
+ this function to use this address without having to worry
+ whether software single step is in use or not. */
+ stop_pc -= DECR_PC_AFTER_BREAK;
+ ecs->random_signal = 0;
+ }
}
else
ecs->random_signal = 1;
Index: breakpoint.c
===================================================================
RCS file: /cvs/src/src/gdb/breakpoint.c,v
retrieving revision 1.78
diff -c -3 -p -r1.78 breakpoint.c
*** breakpoint.c 26 Jun 2002 05:20:04 -0000 1.78
--- breakpoint.c 18 Jul 2002 20:29:42 -0000
*************** bpstat_stop_status (CORE_ADDR *pc, int n
*** 2429,2436 ****
trap event. For a trace/singlestep trap event, we would
not want to subtract DECR_PC_AFTER_BREAK from the PC. */
! bp_addr = *pc - (not_a_breakpoint && !SOFTWARE_SINGLE_STEP_P () ?
! 0 : DECR_PC_AFTER_BREAK);
ALL_BREAKPOINTS_SAFE (b, temp)
{
--- 2429,2435 ----
trap event. For a trace/singlestep trap event, we would
not want to subtract DECR_PC_AFTER_BREAK from the PC. */
! bp_addr = *pc - (not_a_breakpoint ? 0 : DECR_PC_AFTER_BREAK);
ALL_BREAKPOINTS_SAFE (b, temp)
{
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