Fix adjust_pc_after_break, remove still current thread check
On decr_pc_after_break targets, GDB adjusts the PC incorrectly if a
background single-step stops somewhere where PC-$decr_pc has a
breakpoint, and the thread that finishes the step is not the current
thread, like:
ADDR1 nop <-- breakpoint here
ADDR2 jmp PC
IOW, say thread A is stepping ADDR2's line in the background (an
infinite loop), and the user switches focus to thread B. GDB's
adjust_pc_after_break logic confuses the single-step stop of thread A
for a hit of the breakpoint at ADDR1, and thus adjusts thread A's PC
to point at ADDR1 when it should not, and reports a breakpoint hit,
when thread A did not execute the instruction at ADDR1 at all.
The test added by this patch exercises exactly that.
I can't find any reason we'd need the "thread to be examined is still
the current thread" condition in adjust_pc_after_break, at least
nowadays; it might have made sense in the past. Best just remove it,
and rely on currently_stepping().
Here's the test's log of a run with an unpatched GDB:
35 while (1);
(gdb) PASS: gdb.threads/step-bg-decr-pc-switch-thread.exp: next over nop
next&
(gdb) PASS: gdb.threads/step-bg-decr-pc-switch-thread.exp: next& over inf loop
thread 1
[Switching to thread 1 (Thread 0x7ffff7fc2740 (LWP 29027))](running)
(gdb)
PASS: gdb.threads/step-bg-decr-pc-switch-thread.exp: switch to main thread
Breakpoint 2, thread_function (arg=0x0) at ...src/gdb/testsuite/gdb.threads/step-bg-decr-pc-switch-thread.c:34
34 NOP; /* set breakpoint here */
FAIL: gdb.threads/step-bg-decr-pc-switch-thread.exp: no output while stepping
gdb/ChangeLog:
2015-02-11 Pedro Alves <pedro@codesourcery.com>
* infrun.c (adjust_pc_after_break): Don't adjust the PC just
because the event thread is not the current thread.
gdb/testsuite/ChangeLog:
2015-02-11 Pedro Alves <pedro@codesourcery.com>
* gdb.threads/step-bg-decr-pc-switch-thread.c: New file.
* gdb.threads/step-bg-decr-pc-switch-thread.exp: New file.
2015-02-11 09:45:41 +00:00
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# Copyright (C) 2014-2015 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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# On decr_pc_after_break targets, GDB used to adjust the PC
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# incorrectly if a background single-step stopped somewhere where
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# PC-$decr_pc had a breakpoint, and the thread was not the current
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# thread, like:
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#
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# ADDR1 nop <-- breakpoint here
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# ADDR2 jmp PC
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#
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# IOW, say thread A is stepping ADDR2's line in the background (an
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# infinite loop), and the user switches focus to thread B. GDB's
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# adjust_pc_after_break logic would confuse the single-step stop of
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# thread A for a hit of the breakpoint at ADDR1, and thus adjust
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# thread A's PC to point at ADDR1 when it should not: the thread had
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# been single-stepped, not continued.
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standard_testfile
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if {[prepare_for_testing "failed to prepare" $testfile $srcfile {debug pthreads}] == -1} {
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return -1
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}
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clean_restart $binfile
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if ![runto_main] {
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continue
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}
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# Make sure it's GDB's decr_pc logic that's being tested, not the
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# target's.
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gdb_test_no_output "set range-stepping off"
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delete_breakpoints
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gdb_breakpoint [gdb_get_line_number "set breakpoint here"]
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gdb_continue_to_breakpoint "run to nop breakpoint"
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2015-11-24 18:11:21 +00:00
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gdb_test "info threads" " 1 .*\\\* 2 .*" "info threads shows all threads"
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Fix adjust_pc_after_break, remove still current thread check
On decr_pc_after_break targets, GDB adjusts the PC incorrectly if a
background single-step stops somewhere where PC-$decr_pc has a
breakpoint, and the thread that finishes the step is not the current
thread, like:
ADDR1 nop <-- breakpoint here
ADDR2 jmp PC
IOW, say thread A is stepping ADDR2's line in the background (an
infinite loop), and the user switches focus to thread B. GDB's
adjust_pc_after_break logic confuses the single-step stop of thread A
for a hit of the breakpoint at ADDR1, and thus adjusts thread A's PC
to point at ADDR1 when it should not, and reports a breakpoint hit,
when thread A did not execute the instruction at ADDR1 at all.
The test added by this patch exercises exactly that.
I can't find any reason we'd need the "thread to be examined is still
the current thread" condition in adjust_pc_after_break, at least
nowadays; it might have made sense in the past. Best just remove it,
and rely on currently_stepping().
Here's the test's log of a run with an unpatched GDB:
35 while (1);
(gdb) PASS: gdb.threads/step-bg-decr-pc-switch-thread.exp: next over nop
next&
(gdb) PASS: gdb.threads/step-bg-decr-pc-switch-thread.exp: next& over inf loop
thread 1
[Switching to thread 1 (Thread 0x7ffff7fc2740 (LWP 29027))](running)
(gdb)
PASS: gdb.threads/step-bg-decr-pc-switch-thread.exp: switch to main thread
Breakpoint 2, thread_function (arg=0x0) at ...src/gdb/testsuite/gdb.threads/step-bg-decr-pc-switch-thread.c:34
34 NOP; /* set breakpoint here */
FAIL: gdb.threads/step-bg-decr-pc-switch-thread.exp: no output while stepping
gdb/ChangeLog:
2015-02-11 Pedro Alves <pedro@codesourcery.com>
* infrun.c (adjust_pc_after_break): Don't adjust the PC just
because the event thread is not the current thread.
gdb/testsuite/ChangeLog:
2015-02-11 Pedro Alves <pedro@codesourcery.com>
* gdb.threads/step-bg-decr-pc-switch-thread.c: New file.
* gdb.threads/step-bg-decr-pc-switch-thread.exp: New file.
2015-02-11 09:45:41 +00:00
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gdb_test "next" "while.*" "next over nop"
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gdb_test_no_output "next&" "next& over inf loop"
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set test "switch to main thread"
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gdb_test_multiple "thread 1" $test {
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-re "Cannot execute this command while the target is running.*$gdb_prompt $" {
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unsupported $test
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# With remote targets, we can't send any other remote packet
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# until the target stops. Switching thread wants to ask the
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# remote side whether the thread is alive.
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return
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}
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-re "Switching to thread 1.*\\(running\\)\r\n$gdb_prompt " {
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# Prefer to match the prompt without an anchor. If there's a
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# bug and output comes after the prompt immediately, it's
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# faster to handle that in the following test, instead of
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# waiting for a timeout here.
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pass $test
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}
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}
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# Wait a bit. Use gdb_expect instead of sleep so that any (bad) GDB
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# output is visible in the log.
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gdb_expect 4 {}
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set test "no output while stepping"
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gdb_test_multiple "" $test {
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-timeout 1
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timeout {
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pass $test
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}
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-re "." {
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# If we see any output, it's a failure. On the original bug,
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# this would be a breakpoint hit.
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fail $test
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}
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}
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