483805cf9e
If a thread trips on a breakpoint that needs stepping over just after
finishing a step over, GDB currently fails an assertion. This is a
regression caused by the "Handle multiple step-overs." patch
(99619beac6) at
https://sourceware.org/ml/gdb-patches/2014-02/msg00765.html.
(gdb) x /4i $pc
=> 0x400540 <main+4>: movl $0x0,0x2003da(%rip) # 0x600924 <i>
0x40054a <main+14>: movl $0x1,0x2003d0(%rip) # 0x600924 <i>
0x400554 <main+24>: movl $0x2,0x2003c6(%rip) # 0x600924 <i>
0x40055e <main+34>: movl $0x3,0x2003bc(%rip) # 0x600924 <i>
(gdb) PASS: gdb.base/consecutive-step-over.exp: get breakpoint addresses
break *0x40054a
Breakpoint 2 at 0x40054a: file ../../../src/gdb/testsuite/gdb.base/consecutive-step-over.c, line 23.
(gdb) PASS: gdb.base/consecutive-step-over.exp: insn 1: set breakpoint
condition $bpnum condition
(gdb) PASS: gdb.base/consecutive-step-over.exp: insn 1: set condition
break *0x400554
Breakpoint 3 at 0x400554: file ../../../src/gdb/testsuite/gdb.base/consecutive-step-over.c, line 24.
(gdb) PASS: gdb.base/consecutive-step-over.exp: insn 2: set breakpoint
condition $bpnum condition
(gdb) PASS: gdb.base/consecutive-step-over.exp: insn 2: set condition
break *0x40055e
Breakpoint 4 at 0x40055e: file ../../../src/gdb/testsuite/gdb.base/consecutive-step-over.c, line 25.
(gdb) PASS: gdb.base/consecutive-step-over.exp: insn 3: set breakpoint
condition $bpnum condition
(gdb) PASS: gdb.base/consecutive-step-over.exp: insn 3: set condition
break 27
Breakpoint 5 at 0x400568: file ../../../src/gdb/testsuite/gdb.base/consecutive-step-over.c, line 27.
(gdb) continue
Continuing.
../../src/gdb/infrun.c:5200: internal-error: switch_back_to_stepped_thread: Assertion `!tp->control.trap_expected' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
FAIL: gdb.base/consecutive-step-over.exp: continue to breakpoint: break here (GDB internal error)
The assertion fails, because the code is not expecting that the event
thread itself might need another step over. IOW, not expecting that
TP in:
tp = find_thread_needs_step_over (stepping_thread != NULL,
stepping_thread);
could be the event thread.
A small fix for this would be to clear the event thread's
trap_expected earlier, before asserting. But looking deeper, although
currently_stepping_or_nexting_callback's intention is finding the
thread that is doing a step/next, it also returns the thread that is
doing a step-over dance, with trap_expected set. If there ever was a
reason for that (it was I who added
currently_stepping_or_nexting_callback , but I can't recall why I put
trap_expected there in the first place), the only remaining reason
nowadays is to aid in implementing switch_back_to_stepped_thread's
assertion that is now triggering, by piggybacking on the walk over all
threads, thus avoiding a separate walk. This is quite obscure, and I
think we can do even better, by merging the walks that look for the
stepping thread, and the walk that looks for some thread that might
need a step over.
Tested on x86_64 Fedora 17, native and gdbserver, and also native on
top of my "software single-step on x86_64" series.
gdb/
2014-04-22 Pedro Alves <palves@redhat.com>
* infrun.c (schedlock_applies): New function, factored out from
find_thread_needs_step_over.
(find_thread_needs_step_over): Use it.
(switch_back_to_stepped_thread): Always clear trap_expected if the
step over is finished. Return early if scheduler locking applies.
Look for the stepping thread and a potential step-over thread with
a single loop.
(currently_stepping_or_nexting_callback): Delete.
2014-04-22 Pedro Alves <palves@redhat.com>
* gdb.base/consecutive-step-over.c: New file.
* gdb.base/consecutive-step-over.exp: New file.
70 lines
2.2 KiB
Text
70 lines
2.2 KiB
Text
# Copyright 2014 Free Software Foundation, Inc.
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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#
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# Regression test for a bug where GDB would internal error if a thread
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# runs into a breakpoint that needs stepping over, just after stepping
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# over another breakpoint, without a user visible stop in between.
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#
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standard_testfile
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if {[prepare_for_testing "failed to prepare" $testfile $srcfile debug]} {
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return -1
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}
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if ![runto_main] then {
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fail "Can't run to main"
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return 0
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}
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# Make sure the target doesn't hide the breakpoint hits (that don't
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# cause a user visible stop) from GDB.
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gdb_test_no_output "set breakpoint condition-evaluation host"
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set up_to_nl "\[^\r\n\]+\[\r\n\]+"
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# Number of consecutive breakpoints in a row to try.
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set n_insns 3
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# Extract addresses of a few consecutive instructions.
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set test "get breakpoint addresses"
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if { [gdb_test_multiple "x /[expr $n_insns + 1]i \$pc" $test {
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-re "=> $hex${up_to_nl} ($hex)${up_to_nl} ($hex)${up_to_nl} ($hex)${up_to_nl}$gdb_prompt $" {
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for {set i 1} {$i <= $n_insns} {incr i} {
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set bp_addrs($i) $expect_out($i,string)
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}
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pass $test
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}
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}] != 0 } {
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# No use proceeding if bp_addrs wasn't set.
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return
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}
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for {set i 1} {$i <= $n_insns} {incr i} {
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with_test_prefix "insn $i" {
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gdb_test "break \*$bp_addrs($i)" \
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"Breakpoint $decimal at $bp_addrs($i): file .*" \
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"set breakpoint"
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# Give the breakpoint a condition that always fails, so that
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# the thread is immediately re-resumed.
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gdb_test_no_output "condition \$bpnum condition" \
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"set condition"
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}
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}
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set lineno [gdb_get_line_number "break here"]
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gdb_breakpoint $lineno
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gdb_continue_to_breakpoint "break here" ".*break here.*"
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